Adaptation and tolerance of bacteria against acetic acid

Enhancing sanitization for AVB Sepharose resin in AAV vector purification

Affinity chromatography is a critical step in gene therapy for capturing adeno-associated virus (AAV) vectors. However, the high cost of affinity resin needs effective cleaning and sanitization strategies to enable multi-cycle usage. This study evaluated various combinations of cleaning reagents, including alcohol, low concentrations of sodium hydroxide (NaOH), and acids, against a broad range of microbial strains, particularly acid- and alkaline-resistant species, to identify enhanced sanitization protocols for both pre-use and post-use. A solution comprising 100 mM acetic acid with 2 % benzyl alcohol, alongside 10 mM NaOH with 2 % benzyl alcohol, was identified as effective. This new cleaning and sanitization strategy, incorporating both pre- and post-use cleaning, was successfully implemented, allowing for up to six column cycles without product carryover between cycles. Notably, this strategy does not compromise process yield or product quality. It provides effective microbial control during AAV purification using AVB Sepharose resin, while also preserving resin integrity, reducing the risk of microbial contamination and product carryover, lowering AAV manufacturing costs, and ultimately enhancing the quality and reliability of gene therapy product manufacturing.

Evaluation of the Antibacterial Activity of Acetic Acid in Comparison With Three Disinfectants Against Bacteria Isolated From Hospital High-Touch Surfaces

Acetic acid, a readily available and less toxic alternative to conventional disinfectants, is widely used for cleaning in household settings. This study evaluates the antibacterial efficacy of acetic acid against bacteria isolated from hospital high-touch surfaces, comparing its performance to commonly used disinfectants, including phenol, sodium hypochlorite, and didecyldimethylammonium chloride (DDAC). A total of 120 samples were collected from high-touch surfaces in specialized patient areas. The antibacterial activity of acetic acid, phenol, sodium hypochlorite, and DDAC was assessed using the standard broth microdilution method against the isolated bacterial strains. From the 120 samples, 140 bacterial isolates were obtained. Acetic acid demonstrated strong antibacterial activity, with mean minimum inhibitory concentrations (MICs) ranging from 0.05 ± 0.00 to 0.25 ± 0.06 μL/mL, effectively inhibiting coagulase-negative Staphylococcus (CONS), Klebsiella pneumoniae, Proteus vulgaris, Enterococcus species, and Serratia marcescens. Its performance surpassed phenol and DDAC against these strains. Phenol exhibited higher MICs (0.50 ± 0.00 to 0.83 ± 0.10 μL/mL), indicating lower efficacy, while DDAC (0.06 ± 0.00 to 0.17 ± 0.04 μL/mL) and sodium hypochlorite (0.06 ± 0.00 to 0.10 ± 0.00 μL/mL) demonstrated comparable antibacterial effects. Phenol and sodium hypochlorite were found nonsignificant, while DDAC is highly effective at a concentration of 8.5%. Hospital surfaces were found to be contaminated with diverse bacterial strains. Acetic acid demonstrated significant antibacterial efficacy against both gram-positive and gram-negative bacteria, with MICs ranging from 0.05 ± 0.00 to 0.25 ± 0.06 μL/mL, suggesting its potential as an effective, economical, and less toxic alternative to conventional disinfectants.

Isolation and Characterization of Komagataeibacter piraceti sp. nov. and Novacetimonas labruscae sp. nov.: Two Novel Microaerobic Cellulose-Producing Acetic Acid Bacteria from Vinegars

The genera Komagataeibacter and Novacetimonas comprise industrially important species that produce various foods, nanocellulose, acetan-like polysaccharides, enantioselective sugars, and other valuable products. Here, we describe two novel strains, Hr1 and Jurk4, isolated from pear and apple-grape organic vinegars that showed very high (≥99.39%) 16S rRNA gene sequence identities to species of the Komagataeibacter and Novacetimonas genera, respectively. However, analysis of the 16S-23S rRNA gene internal transcribed spacer (ITS) sequences revealed only 92.6% sequence identity between the Hr1 strain and its closest relative, Komagataeibacter sucrofermentans LMG 18788T, and 93.8% sequence identity between the Jurk4 strain and its closest relative, Novacetimonas cocois JCM 31140T. Further whole-genome analysis showed for both strains an average nucleotide identity (ANI) below 94% and an in silico DNA-DNA hybridization (dDDH) value of less than 70% to their closest species, supporting their distinction as novel species. The strain Hr1 can be phenotypically differentiated from its closest Komagataeibacter species based on its ability to utilize (NH4)2SO4 as the sole nitrogen source in Asai medium with D-glucose and its inability to grow with 1-propanol as a sole carbon source. The strain Jurk4 can be differentiated from other Novacetimonas type strains based on its ability to produce 5-keto-D-gluconic acid, its growth in a medium with glycerol as the sole carbon source, and its inability to grow in an Asai medium with D-glucose. Both strains produce cellulose and possess clusters for acetane-like polysaccharide production, although of different types, which makes them industrially relevant. Based on these findings, we propose Komagataeibacter piraceti sp. nov. Hr1T (=ZIM B1167T = LMG 33628T) and Novacetimonas labruscae sp. nov. Jurk4T (=ZIM B1166T = LMG 33630T) as two novel members of the acetic acid bacteria group.

Deciphering the function of Fe3O4 in alleviating propionate inhibition during high-solids anaerobic digestion: Insights of physiological response and energy conservation

Fe3O4 is a recognized addictive to enhance low solid anaerobic digestion (AD), while for high solid AD challenged by acidity inhibition, its feasibility and mechanism remain unclear. In this study, the positive effect of Fe3O4 on high-solids AD of food waste by regulating microbial physiology and energy conservation to enhance mutualistic propionate methanation was documented. The methane yield was increased by 36.7 % with Fe3O4, which because Fe3O4 alleviated propionate stress on methane generation, along with improved propionate degradation and methanogenic metabolism. Fe3O4 facilitated the production of extracellular polymeric substances and the formation of tightly bio-aggregates, fostering an enriched microbial population (e.g., Smithella and Methanosaeta) to resist propionate stress. Also, Fe3O4 up-regulated the genes in stress defense system, cytomembrane biosynthesis/function, metal irons transporter, cell division and enzyme synthesis, verifying its superiority on cellular physiology. In addition, energy-conservation strategies related to intracellular and extracellular electron transfer were enhanced by Fe3O4. Specifically, the enzyme expressions involved in reversed electron transfer and electron bifurcation coupled with direct interspecies electron transfer (DIET) were upregulated by at least 2.2 times with Fe3O4, providing sufficient energy to drive thermodynamic adverse methanogenesis from propionate-stressed condition. Consequently, the reinforced enzyme expression in the dismutation and DIET pathway make it to be the predominant drivers for enhanced methanogenic propionate metabolism. This study fills the knowledge gaps of Fe3O4-induced microbial physiological and energetic strategies to resist environmental stress, and has remarkable practical implicated for restoring inhibited bioactivities.

Beyond nutritional immunity: immune-stressing challenges basic paradigms of immunometabolism and immunology

Pathogens have the well-known advantage of rapid evolution due to short generation times and large populations. However, pathogens have the rarely noted disadvantage of the vulnerability to stress involved in proliferation as well as being localized. Presented here are numerous new paradigms in immunology, and especially immunometabolism, which are derived from examining how hosts capitalize on pathogen vulnerabilities to stress. Universally, proliferation requires both resources and synthesis, which are vulnerable to resource-limiting stress and damaging/noxious stress, respectively. Pathogens are particularly vulnerable to stress at the time when they are most threatening-when they are proliferating. Since immune cells actively controlling pathogens (effector cells) typically do not proliferate at infected sites, there is a "stress vulnerability gap" wherein proliferating pathogens are more vulnerable to any type of stress than are the attacking effector cells. Hosts actively stress vulnerable proliferating pathogens by restricting resources (resource-limiting stress) and generating noxious waste products (damaging/disruptive stress) in a fundamental defense here-in termed "immune-stressing." While nutritional immunity emphasizes denying pathogens micronutrients, immune-stressing extends the concept to restricting all resources, especially glucose and oxygen, coupled with the generation of noxious metabolic products such as lactic acid, reactive oxygen species (ROS), and heat to further harm or stress the pathogens. At present much of the field of immunometabolism centers on how nutrition and metabolism regulate immune function, a central feature being the inefficient use of glucose via aerobic glycolysis (with much lactate/lactic acid production) by effector immune cells. In contrast, immune-stressing emphasizes how the immune system uses nutrition and metabolism to control infections. Immune-stressing addresses effector cell glycolysis at the infected site by noting that the high uptake of glucose linked with high output of lactic acid is an ideal double-pronged stressor targeting proliferating pathogens. Once the basic vulnerability of pathogen proliferation is recognized, numerous other paradigms of immunometabolism, and immunology as a whole, are challenged.

Increased distribution of carbon metabolic flux during de novo cytidine biosynthesis via attenuation of the acetic acid metabolism pathway in Escherichia coli

Acetic acid, a by-product of cytidine synthesis, competes for carbon flux from central metabolism, which may be directed either to the tricarboxylic acid (TCA) cycle for cytidine synthesis or to overflow metabolites, such as acetic acid. In Escherichia coli, the acetic acid synthesis pathway, regulated by the poxB and pta genes, facilitates carbon consumption during cytidine production. To mitigate carbon source loss, the CRISPR-Cas9 gene-editing technique was employed to knock out the poxB and pta genes in E. coli, generating the engineered strains K12ΔpoxB and K12ΔpoxBΔpta. After 39 h of fermentation in 500 mL shake flasks, the cytidine yields of strains K12ΔpoxB and K12ΔpoxBΔpta were 1.91 ± 0.04 g/L and 18.28 ± 0.22 g/L, respectively. Disruption of the poxB and pta genes resulted in reduced acetic acid production and glucose consumption. Transcriptomic and metabolomic analyses revealed that impairing the acetic acid metabolic pathway in E. coli effectively redirected carbon flux toward cytidine biosynthesis, yielding a 5.26-fold reduction in acetate metabolism and an 11.56-fold increase in cytidine production. These findings provide novel insights into the influence of the acetate metabolic pathway on cytidine biosynthesis in E. coli.

Uses of Chemical Technologies for Meat Decontamination

Traditional meat preservation techniques such as smoking, drying, and salting have various shortcomings and limitations in effectively reducing microbial loads and maintaining meat quality. Consequently, chemical compounds have gained attention as promising alternatives for decontamination, offering the potential to extend shelf life and minimize physical, chemical, and sensory changes in meat. Chlorine-based compounds, trisodium phosphate, organic acids, bacteriocins, lactoferrin, and peracetic acid are technologies of recent industrial applications that inhibit spoilage and pathogenic microorganisms in meat. This review explores the critical aspects of decontamination and assesses the efficacy of different chemical compounds employed in meat preservation. These compounds exhibit strong microorganism inactivation capabilities, ensuring minimal alterations to the meat matrix and substantially reducing environmental impact.

Probiotic Mixture Attenuates Colorectal Tumorigenesis in Murine AOM/DSS Model by Suppressing STAT3, Inducing Apoptotic p53 and Modulating Gut Microbiota

Colorectal cancer (CRC) is one of the most common cancers worldwide. The standard CRC chemo drug, 5-Fluorouracil (5-FU), has a poor response rate and chemoresistance, prompting the need for a more effective and affordable treatment. In this study, we aimed to evaluate whether Prohep, a novel probiotic mixture, would alleviate azoxymethane/dextran sodium sulfate (AOM/DSS)-induced colorectal tumorigenesis and enhance 5-FU efficacy and its mechanism. Our results suggested that Prohep showed stronger anti-tumorigenesis effects than 5-FU alone or when combined in the AOM/DSS model. Prohep significantly reduced the total tumor count, total tumor size, caecum weight, colonic crypt depth, colonic inflammation, and collagen fibrosis. Prohep downregulated pro-inflammatory TNF-α and proliferative p-STAT3 and upregulated apoptotic p53. Metagenomics analysis indicated that Prohep-enriched Helicobacter ganmani, Desulfovibrio porci, Helicobacter hepaticus, and Candidatus Borkfalkia ceftriaxoniphila were inversely correlated to the total tumor count. In addition, Prohep-enriched Prevotella sp. PTAC and Desulfovibrio porci were negatively correlated to AOM/DSS enriched bacteria, while forming a co-existing community with other beneficial bacteria. From KEGG analysis, Prohep downregulated CRC-related pathways and enhanced pathways related to metabolites suppressing CRC like menaquinone, tetrapyrrole, aminolevulinic acid, and tetrahydrofolate. From Metacyc analysis, Prohep downregulated CRC-related peptidoglycan, LPS, and uric acid biosynthesis, and conversion. Prohep elevated the biosynthesis of the beneficial L-lysine, lipoic acid, pyrimidine, and palmitate. Prohep also elevated metabolic pathways related to energy utilization of lactic acid-producing bacteria (LAB) and acetate producers. Similarly, fecal acetate concentration was upregulated by Prohep. To sum up, Prohep demonstrated exceptional anti-tumorigenesis effects in the AOM/DSS model, which revealed its potential to develop into a novel CRC therapeutic in the future.

Proanthocyanidins and volatile aroma of cranberry juice are modulated by its microbiota and processing environment

The quality and sensory attributes of juices are influenced by their natural microbiota and the microorganisms found on filtration membranes. This study aimed to assess the influence of natural microbiota and specific contaminants, including Candida krusei, Rhodotorula mucilaginosa, Debaryomyces prosopidis, Ralstonia insidiosa, and Lactiplantibacillus paraplantarum, isolated from cranberry juice and its associated industrial filtration membranes, on the characteristics of cranberry juice. Their growth kinetics and impacts on total phenols, total anthocyanins, total proanthocyanins, total organic acids, pH, titratable acidity, and volatile compounds were assessed. During the 42 h fermentation period, Candida krusei and Ralstonia insidiosa exhibited significant growth, increasing by 1-log and 3-log, respectively. The natural microbiota led to a 7% and 6% reduction in anthocyanins and proanthocyanidins, while Candida krusei and Rhodotorula mucilaginosa caused losses of 10% and 7% in proanthocyanidins, respectively. Organic acid content remained stable, except for an 8% decrease caused by Ralstonia insidiosa. Volatile compounds underwent significant increases, particularly in green (703%), winey (100%), mushroom (306%), and fusel (2678%) notes. These findings underscore the rapid impact of microorganisms from natural microbiota and filtration membranes on cranberry juice characteristics, highlighting the importance for beverage industries to prioritize customer safety and satisfaction.

Regulatory mechanisms of acetic acid, ethanol and high temperature tolerances of acetic acid bacteria during vinegar production

Acetic acid bacteria (AAB) play a pivotal role in the food fermentation industry, especially in vinegar production, due to their ability to partially oxidize alcohols to acetic acid. However, economic bioproduction using AAB is challenged by harsh environments during acetic acid fermentation, among which initial ethanol pressure, subsequent acetic acid pressure, and consistently high temperatures are common experiences. Understanding the stress-responsive mechanisms is essential to developing robust AAB strains. Here, we review recent progress in mechanisms underlying AAB stress response, including changes in cell membrane composition, increased activity of membrane-bound enzymes, activation of efflux systems, and the upregulation of stress response molecular chaperones. We also discuss the potential of advanced technologies, such as global transcription machinery engineering (gTME) and Design-Build-Test-Learn (DBTL) approach, to enhance the stress tolerance of AAB, aiming to improve vinegar production.

Role of the cathode chamber in microbial electrosynthesis: A comprehensive review of key factors

The consumption of non-renewable fossil fuels has directly contributed to a dramatic rise in global carbon dioxide (CO2) emissions, posing an ongoing threat to the ecological security of the Earth. Microbial electrosynthesis (MES) is an innovative energy regeneration strategy that offers a gentle and efficient approach to converting CO2 into high-value products. The cathode chamber is a vital component of an MES system and its internal factors play crucial roles in improving the performance of the MES system. Therefore, this review aimed to provide a detailed analysis of the key factors related to the cathode chamber in the MES system. The topics covered include inward extracellular electron transfer pathways, cathode materials, applied cathode potentials, catholyte pH, and reactor configuration. In addition, this review analyzes and discusses the challenges and promising avenues for improving the conversion of CO2 into high-value products via MES.

Achieving robust synthetic tolerance in industrial E. coli through negative auto-regulation of a DsrA-Hfq module

In industrial fermentation processes, microorganisms often encounter acid stress, which significantly impact their productivity. This study focused on the acid-resistant module composed of small RNA (sRNA) DsrA and the sRNA chaperone Hfq. Our previous study had shown that this module improved the cell growth of Escherichia coli MG1655 at low pH, but failed to obtain this desired phenotype in industrial strains. Here, we performed a quantitative analysis of DsrA-Hfq module to determine the optimal expression mode. We then assessed the potential of the CymR-based negative auto-regulation (NAR) circuit for industrial application, under different media, strains and pH levels. Growth assay at pH 4.5 revealed that NAR-05D04H circuit was the best acid-resistant circuit to improve the cell growth of E. coli MG1655. This circuit was robust and worked well in the industrial lysine-producing strain E. coli SCEcL3 at a starting pH of 6.8 and without pH control, resulting in a 250 % increase in lysine titer and comparable biomass in shaking flask fermentation compared to the parent strain. This study showed the practical application of NAR circuit in regulating DsrA-Hfq module, effectively and robustly improving the acid tolerance of industrial strains, which provides a new approach for breeding industrial strains with tolerance phenotype.

Viability and Diversity of the Microbial Cultures Available in Retail Kombucha Beverages in the USA

Kombucha is a two-stage fermented sweetened tea beverage that uses yeast and lactic acid bacteria (LAB) to convert sugars into ethanol and lactate and acetic acid bacteria (AAB) to oxidize ethanol to acetate. Its popularity as a beverage grew from claims of health benefits derived from this vibrant microbial bioconversion. While recent studies have shed light on the diversity of cultures in Kombucha fermentation, there is limited information on the diversity, and especially viability, of cultures in retail beverages that advertise the presence of Kombucha and probiotic cultures. In this study, 12 Kombucha beverages produced by different manufacturers throughout the US were purchased and microbially characterized. Eight of the beverages contained viable Kombucha cultures, while 3 of the remaining 4 had viable Bacillus cultures as added probiotics. Amplicon profiling revealed that all contained Kombucha yeast and bacteria cells. The dominant yeasts detected were Lachancea cidri (10/12), Brettanomyces (9/12), Malassezia (6/12), and Saccharomyces (5/12). Dominant LAB included Liquorilactobacillus and Oenococcus oeni, and AAB were Komagataeibacter, Gluconobacter, and Acetobacter. One beverage had a significant amount of Zymomonas mobilis, an ethanol-producing bacterium from Agave cactus. While Kombucha beverages differ in the types and viability of cultures, all except one beverage contained detectable viable cells.

Why does increased microbial fermentation in the human colon shift toward butyrate?

The microbial community of the human large intestine mainly ferments dietary fiber to short chain fatty acids (SCFAs), which are efficiently absorbed by the host. The three major SCFAs (acetate, propionate, and butyrate) have different fates within the body and different effects on health. A recent analysis of 10 human volunteer studies established that the proportions of these SCFA in fecal samples significantly shifted towards butyrate as the overall concentration of SCFA increased. Butyrate plays a key role in gut health and is preferentially utilized as an energy source by the colonic epithelium. Here we discuss possible mechanisms that underlie this 'butyrate shift'; these include the selection for butyrate-producing bacteria within the microbiota by certain types of fiber, and the possibility of additional butyrate formation from lactate and acetate by metabolite cross-feeding. However, a crucial factor appears to be the pH in the proximal colon, which decreases as the SCFA concentrations increase. A mildly acidic pH has been shown to have an important impact on microbial competition and on the stoichiometry of butyrate production. Understanding these complex interactions has been greatly aided by the refinement of theoretical models of the colonic microbiota that assume a small number (10) of microbial functional groups (MFGs).

Successive process for efficient biovalorization of Brewers' spent grain to lignocellulolytic enzymes and lactic acid production through simultaneous saccharification and fermentation

This study aimed to increase the value of brewers' spent grain (BSG) by using it as feedstock to produce lignocellulolytic enzymes and lactic acid (LA). Twenty-two fungal strains were screened for lignocellulolytic enzyme production from BSG. Among them, Trichoderma sp. showed the highest cellulase activity (35.84 ± 0.27 U/g-BSG) and considerably high activities of xylanase (599.61 ± 23.09 U/g-BSG) and β-glucosidase (16.97 ± 0.77 U/g-BSG) under successive solid-state and submerged fermentation. The processes were successfully scaled up in a bioreactor. The enzyme cocktail was recovered and characterized. The maximum cellulase and xylanase activities were found at pH 5.0 and 50 °C, and the activities were highly stable at pH 4-8 and 30-50 °C. The enzyme cocktail was applied in simultaneous saccharification and fermentation of acid-pretreated BSG for LA production. The maximum LA obtained was 59.3 ± 1.0 g/L. This study has shown the efficient biovalorization of BSG, and this approach may also be applicable to other agro-industrial wastes.

Acetic acid stress response of the acidophilic sulfate reducer Acididesulfobacillus acetoxydans

Acid mine drainage (AMD) waters are a severe environmental threat, due to their high metal content and low pH (pH <3). Current technologies treating AMD utilize neutrophilic sulfate-reducing microorganisms (SRMs), but acidophilic SRM could offer advantages. As AMDs are low in organics these processes require electron donor addition, which is often incompletely oxidized into organic acids (e.g., acetic acid). At low pH, acetic acid is undissociated and toxic to microorganisms. We investigated the stress response of the acetotrophic Acididesulfobacillus acetoxydans to acetic acid. A. acetoxydans was cultivated in bioreactors at pH 5.0 (optimum). For stress experiments, triplicate reactors were spiked until 7.5 mM of acetic acid and compared with (non-spiked) triplicate reactors for physiological, transcriptomic, and membrane lipid changes. After acetic acid spiking, the optical density initially dropped, followed by an adaptation phase during which growth resumed at a lower growth rate. Transcriptome analysis revealed a downregulation of genes involved in glutamate and aspartate synthesis following spiking. Membrane lipid analysis revealed a decrease in iso and anteiso fatty acid relative abundance; and an increase of acetyl-CoA as a fatty acid precursor. These adaptations allow A. acetoxydans to detoxify acetic acid, creating milder conditions for other microorganisms in AMD environments.

Fermentative processes for the upcycling of xylose to xylitol by immobilized cells of Pichia fermentans WC1507

Xylitol is a pentose-polyol widely applied in the food and pharmaceutical industry. It can be produced from lignocellulosic biomass, valorizing second-generation feedstocks. Biotechnological production of xylitol requires scalable solutions suitable for industrial scale processes. Immobilized-cells systems offer numerous advantages. Although fungal pellet carriers have gained attention, their application in xylitol production remains unexplored. In this study, the yeast strain P. fermentans WC 1507 was employed for xylitol production. The optimal conditions were observed with free-cell cultures at pH above 3.5, low oxygenation, and medium containing (NH4)2SO4 and yeast extract as nitrogen sources (xylitol titer 79.4 g/L, YP/S 66.3%, and volumetric productivity 1.3 g/L/h). Yeast cells were immobilized using inactive Aspergillus oryzae pellet mycelial carrier (MC) and alginate beads (AB) and were tested in flasks over three consecutive production runs. Additionally, the effect of a 0.2% w/v alginate layer, coating the outer surface of the carriers (cMC and cAB, respectively), was examined. While YP/S values observed with both immobilized and free cells were similar, the immobilized cells exhibited lower final xylitol titer and volumetric productivity, likely due to mass transfer limitations. AB and cAB outperformed MC and cMC. The uncoated AB carriers were tested in a laboratory-scale airlift bioreactor, which demonstrated a progressive increase in xylitol production in a repeated batch process: in the third run, a xylitol titer of 63.0 g/L, YP/S of 61.5%, and volumetric productivity of 0.52 g/L/h were achieved. This study confirmed P. fermentans WC 1507 as a promising strain for xylitol production in both free- and entrapped-cells systems. Considering the performance of the wild strain, a metabolic engineering intervention aiming at further improving the efficiency of xylitol production could be justified. MC and AB proved to be viable supports for cell immobilization, but additional process development is necessary to identify the optimal bioreactor configuration and fermentation conditions.

Investigation of Acid Tolerance Mechanism of Acetobacter pasteurianus under Different Concentrations of Substrate Acetic Acid Based on 4D Label-Free Proteomic Analysis

Acetobacter pasteurianus is always used to brew vinegar because of its ability of producing and tolerating a high concentration of acetic acid. During vinegar fermentation, initial acetic acid contributes to acetic acid accumulation, which varies with initial concentrations. In this study, to investigate the mechanisms of tolerating and producing acetic acid of Acetobacter pasteurianus under different concentrations of substrate acetic acid, four-dimensional label-free proteomic technology has been used to analyze the protein profiles of Acetobacter pasteurianus at different growth stages (the lag and exponential phases) and different substrate acetic acid concentrations (0%, 3%, and 6%). A total of 2093 proteins were quantified in this study. The differentially expressed proteins were majorly involved in gene ontology terms of metabolic processes, cellular metabolic processes, and substance binding. Under acetic acid stress, strains might attenuate the toxicity of acetic acid by intensifying fatty acid metabolism, weakening the tricarboxylic acid cycle, glycerophospholipid and energy metabolism during the lag phase, while strains might promote the assimilation of acetic acid and inter-conversion of substances during the exponential phase by enhancing the tricarboxylic acid cycle, glycolysis, pyruvate, and energy metabolism to produce and tolerate acid. Besides, cell cycle regulation and protein translation might be potential acid tolerance pathways under high acid stress. The result contributes to the exploration of new potential acid tolerance mechanisms in Acetobacter pasteurianus from four-dimensional label-free relative quantitative proteomics analysis.

Syntrophic entanglements for propionate and acetate oxidation under thermophilic and high-ammonia conditions

Propionate is a key intermediate in anaerobic digestion processes and often accumulates in association with perturbations, such as elevated levels of ammonia. Under such conditions, syntrophic ammonia-tolerant microorganisms play a key role in propionate degradation. Despite their importance, little is known about these syntrophic microorganisms and their cross-species interactions. Here, we present metagenomes and metatranscriptomic data for novel thermophilic and ammonia-tolerant syntrophic bacteria and the partner methanogens enriched in propionate-fed reactors. A metagenome for a novel bacterium for which we propose the provisional name 'Candidatus Thermosyntrophopropionicum ammoniitolerans' was recovered, together with mapping of its highly expressed methylmalonyl-CoA pathway for syntrophic propionate degradation. Acetate was degraded by a novel thermophilic syntrophic acetate-oxidising candidate bacterium. Electron removal associated with syntrophic propionate and acetate oxidation was mediated by the hydrogen/formate-utilising methanogens Methanoculleus sp. and Methanothermobacter sp., with the latter observed to be critical for efficient propionate degradation. Similar dependence on Methanothermobacter was not seen for acetate degradation. Expression-based analyses indicated use of both H2 and formate for electron transfer, including cross-species reciprocation with sulphuric compounds and microbial nanotube-mediated interspecies interactions. Batch cultivation demonstrated degradation rates of up to 0.16 g propionate L-1 day-1 at hydrogen partial pressure 4-30 Pa and available energy was around -20 mol-1 propionate. These observations outline the multiple syntrophic interactions required for propionate oxidation and represent a first step in increasing knowledge of acid accumulation in high-ammonia biogas production systems.

Mechanistic insights into Fe3O4-modified biochar relieving inhibition from erythromycin on anaerobic digestion

Anaerobic digestion (AD) of antibiotic manufacturing wastewater to degrade residual antibiotics and produce mixture of combustible gases has been investigated actively in the past decades. However, detrimental effect of residual antibiotic to microbial activities is commonly faced in AD process, leading to the reduction of treatment efficiency and energy recovery. Herein, the present study systematically evaluated the detoxification effect and mechanism of Fe3O4-modified biochar in AD of erythromycin manufacturing wastewater. Results showed that Fe3O4-modified biochar had stimulatory effect on AD at 0.5 g/L erythromycin existence. A maximum methane yield of 327.7 ± 8.0 mL/g COD was achieved at 3.0 g/L Fe3O4-modified biochar, leading to the increase of 55.7% compared to control group. Mechanistic investigation demonstrated that different levels of Fe3O4-modified biochar could improve methane yield via different metabolic pathways involved in specific bacteria and archaea. Low levels of Fe3O4-modified biochar (i.e., 0.5-1.0 g/L) led to the enrichment of Methanothermobacter sp., strengthening the hydrogenotrophic pathway. On the contrary, high levels of Fe3O4-modified biochar (2.0-3.0 g/L) favored the proliferation of acetogens (e.g., Lentimicrobium sp.) and methanogen (Methanosarcina sp.) and their syntrophic relations played vital role on the simulated AD performance at erythromycin stress. Additionally, the addition of Fe3O4-modified biochar significantly decreased the abundance of representative antibiotic resistant genes (ARGs), benefiting the reduction of environmental risk. The results of this study verified that the application of Fe3O4-modified biochar could be an efficient approach to detoxify erythromycin on AD system, which brings high impacts and positive implications for biological antibiotic wastewater treatment.

Latest Trends in Industrial Vinegar Production and the Role of Acetic Acid Bacteria: Classification, Metabolism, and Applications-A Comprehensive Review

Vinegar is one of the most appreciated fermented foods in European and Asian countries. In industry, its elaboration depends on numerous factors, including the nature of starter culture and raw material, as well as the production system and operational conditions. Furthermore, vinegar is obtained by the action of acetic acid bacteria (AAB) on an alcoholic medium in which ethanol is transformed into acetic acid. Besides the highlighted oxidative metabolism of AAB, their versatility and metabolic adaptability make them a taxonomic group with several biotechnological uses. Due to new and rapid advances in this field, this review attempts to approach the current state of knowledge by firstly discussing fundamental aspects related to industrial vinegar production and then exploring aspects related to AAB: classification, metabolism, and applications. Emphasis has been placed on an exhaustive taxonomic review considering the progressive increase in the number of new AAB species and genera, especially those with recognized biotechnological potential.

Unraveling the Role of Metals and Organic Acids in Bacterial Antimicrobial Resistance in the Food Chain

Antimicrobial resistance (AMR) has a significant impact on human, animal, and environmental health, being spread in diverse settings. Antibiotic misuse and overuse in the food chain are widely recognized as primary drivers of antibiotic-resistant bacteria. However, other antimicrobials, such as metals and organic acids, commonly present in agri-food environments (e.g., in feed, biocides, or as long-term pollutants), may also contribute to this global public health problem, although this remains a debatable topic owing to limited data. This review aims to provide insights into the current role of metals (i.e., copper, arsenic, and mercury) and organic acids in the emergence and spread of AMR in the food chain. Based on a thorough literature review, this study adopts a unique integrative approach, analyzing in detail the known antimicrobial mechanisms of metals and organic acids, as well as the molecular adaptive tolerance strategies developed by diverse bacteria to overcome their action. Additionally, the interplay between the tolerance to metals or organic acids and AMR is explored, with particular focus on co-selection events. Through a comprehensive analysis, this review highlights potential silent drivers of AMR within the food chain and the need for further research at molecular and epidemiological levels across different food contexts worldwide.

Exploring Peracetic Acid and Acidic pH Tolerance of Antibiotic-Resistant Non-Typhoidal Salmonella and Enterococcus faecium from Diverse Epidemiological and Genetic Backgrounds

Acid stress poses a common challenge for bacteria in diverse environments by the presence of inorganic (e.g., mammals' stomach) or organic acids (e.g., feed additives; acid-based disinfectants). Limited knowledge exists regarding acid-tolerant strains of specific serotypes, clonal lineages, or sources in human/animal pathogens: namely, non-typhoidal Salmonella enterica (NTS) and Enterococcus faecium (Efm). This study evaluated the acidic pH (Mueller-Hinton acidified with HCl) and peracetic acid (PAA) susceptibility of Efm (n = 72) and NTS (n = 60) from diverse epidemiological/genetic backgrounds and with multiple antibiotic resistance profiles. Efm minimum growth/survival pH was 4.5-5.0/3.0-4.0, and for NTS it was 4.0-4.5/3.5-4.0. Efm distribution among acidic pH values showed that only isolates of clade-non-A1 (non-hospital associated) or the food chain were more tolerant to acidic pH compared to clade-A1 (hospital-associated clones) or clinical isolates (p < 0.05). In the case of NTS, multidrug-resistant (MDR) isolates survived better in acidic pH (p < 0.05). The PAA MIC/MBC for Efm was 70-120/80-150 mg/L, and for NTS, it was 50-70/60-100 mg/L. The distribution of Efm among PAA concentrations showed that clade-A1 or MDR strains exhibited higher tolerance than clade-non-A1 or non-MDR ones (p < 0.05). NTS distribution also showed higher tolerance to PAA among non-MDR and clinical isolates than food chain ones (p < 0.05) but there were no differences among different serogroups. This unique study identifies specific NTS or Efm populations more tolerant to acidic pH or PAA, emphasizing the need for further research to tailor controlled measures of public health and food safety within a One Health framework.

Effect of lactic acid bacteria on the structure and potential function of the microbial community of Nongxiangxing Daqu

OBJECTIVES

The microbial community structure of the saccharifying starter, Nongxiangxing Daqu(Daqu), is a crucial factor in determining Baijiu's quality. Lactic acid bacteria (LAB), are the dominant microorganisms in the Daqu. The present study investigated the effects of LAB on the microbial community structure and its contribution to microbial community function during the fermentation of Daqu.

METHODS

The effect of LAB on the structure and function of the microbial community of Daqu was investigated using high-throughput sequencing technology combined with multivariate statistical analysis.

RESULTS

LAB showed a significant stage-specific evolution pattern during Daqu fermentation. The LEfSe analysis and the random forest learning algorithm identified LAB as vital differential microorganisms during Daqu fermentation. The correlation co-occurrence network showed aggregation of LAB and Daqu microorganisms, indicating LAB's significant position in influencing the microbial community structure, and suggests that LAB showed negative correlations with Bacillus, Saccharopolyspora, and Thermoactinomyces but positive correlations with Issatchenkia, Candida, Acetobacter, and Gluconobacter. The predicted genes of LAB enriched 20 functional pathways during Daqu fermentation, including Biosynthesis of amino acids, Alanine, aspartate and glutamate metabolism, Valine, leucine and isoleucine biosynthesis and Starch and sucrose metabolism, which suggested that LAB had the functions of polysaccharide metabolism and amino acid biosynthesis.

CONCLUSION

LAB are important in determining the composition and function of Daqu microorganisms, and LAB are closely related to the production of nitrogenous flavor substances in Daqu. The study provides a foundation for further exploring the function of LAB and the regulation of Daqu quality.

Deciphering the brewing process of Cantonese-style rice vinegar: Main flavors, key physicochemical factors, and important microorganisms

Cantonese-style rice vinegar is one of the most important Chinese rice vinegars and is quite popular all over the southeast coast of China, especially in Guangdong. This study identified 31 volatile compounds, including 11 esters, 6 alcohols, 3 aldehydes, 3 acids, 2 ketones, 1 phenol, and 5 alkanes, using headspace solid-phase microextraction-gas chromatography-mass spectrometry. Six organic acids were detected by high performance liquid chromatography. The ethanol content was detected by gas chromatography. During acetic acid fermentation, physicochemical analysis showed that the initial concentrations of reducing sugar and ethanol were 0.0079 g/L and 23.81 g/L, respectively, and the final value of total acid was 46.5 g/L, and the pH value was stable at 3.89. High-throughput sequencing was used to identify the microorganisms, and Acetobacter, Komagataeibacter, and Ralstonia were the top three bacterial genera. Quantitative real-time polymerase chain reaction revealed patterns that were different from those of high-throughput sequencing. The co-occurrence network of microorganisms and the correlation analysis between microorganisms and flavor substances indicate that Acetobacter and Ameyamaea played crucial roles as the main functional AAB, and the failure of Cantonese-style rice vinegar fermentation can be attributed to the abnormal increase in Komagataeibacter. Microbial co-occurrence network analysis indicated that Oscillibacter, Parasutterella, and Alistipes were the top three microorganisms. Redundancy analysis disclosed that total acid and ethanol were the key environmental factors influencing the microbial community. Fifteen microorganisms closely related to the metabolites were identified using the bidirectional orthogonal partial least squares model. Correlation analysis showed that these microorganisms were strongly associated with flavor metabolites and environmental factors. The findings of this study deepen our understanding of the fermentation of traditional Cantonese-style rice vinegar.

Response surface optimization of poly-β-hydroxybutyrate synthesized by Bacillus cereus L17 using acetic acid as carbon source

A strain of Bacillus that can tolerate 10 g/L acetic acid and use the volatile fatty acids produced by the hydrolysis and acidification of activated sludge to produce polyhydroxyalkanoate was screened from the activated sludge of propylene oxide saponification wastewater. The strain was identified by 16S rRNA sequencing and phylogenetic tree analysis and was named Bacillus cereus L17. Various characterization methods showed that the polymer synthesized by strain L17 is poly-β-hydroxybutyrate, which has low crystallinity, good ductility and toughness, high thermal stability and a low polydispersity coefficient. It has wide thermoplastic material operating space as well as industrial and medicinal applications. The optimal fermentation conditions were determined by single factor optimization. Then, Plackett-Burman and Box-Behnken design experiments were carried out according to the single factor optimization results, and the response surface optimization was completed. The final results were: initial pH 6.7, temperature 25 °C, and loading volume 124 mL. The verification experiment showed that the yield of poly-β-hydroxybutyrate after optimization increased by 35.2 % compared to that before optimization.

From Nature to Lab: Sustainable Bacterial Cellulose Production and Modification with Synthetic Biology

Bacterial cellulose (BC) is a macromolecule with versatile applications in medicine, pharmacy, biotechnology, cosmetology, food and food packaging, ecology, and electronics. Although many bacteria synthesize BC, the most efficient BC producers are certain species of the genera Komagataeibacter and Novacetimonas. These are also food-grade bacteria, simplifying their utilization at industrial facilities. The basic principles of BC synthesis are known from studies of Komagataeibacter xylinus, which became a model species for studying BC at genetic and molecular levels. Cellulose can also be of plant origin, but BC surpasses its purity. Moreover, the laboratory production of BC enables in situ modification into functionalized material with incorporated molecules during its synthesis. The possibility of growing Komagataeibacter and Novacetimonas species on various organic substrates and agricultural and food waste compounds also follows the green and sustainable economy principles. Further intervention into BC synthesis was enabled by genetic engineering tools, subsequently directing it into the field of synthetic biology. This review paper presents the development of the fascinating field of BC synthesis at the molecular level, seeking sustainable ways for its production and its applications towards genetic modifications of bacterial strains for producing novel types of living biomaterials using the flexible metabolic machinery of bacteria.

Development and Comparative Evaluation of Ciprofloxacin Nanoemulsion-Loaded Bigels Prepared Using Different Ratios of Oleogel to Hydrogels

Nanoemulsions and bigels are biphasic delivery systems that can be used for topical applications. The aim of this study was to incorporate an oil-in-water ciprofloxacin hydrochloride nanoemulsion (CIP.HCl NE) into two types of bigels, Type I (oleogel (OL)-in-hydrogel (WH)) and Type II (WH-in-OL) to enhance drug penetration into skin and treat topical bacterial infections. Bigels were prepared at various ratios of OL and WH (1:1, 1:2, and 1:4). Initially, CIP.HCl NE was prepared and characterized in terms of droplet size, zeta potential, polydispersity index, morphology, and thermodynamic and chemical stability. Then CIP.HCl NE was dispersed into the OL or WH phase of the bigel. The primary physical stability studies showed that Type I bigels were physically stable, showing no phase separation. Whereas Type II bigels were physically unstable, hence excluded from the study. Type I bigels were subjected to microstructural, rheological, in vitro release, antimicrobial, and stability studies. The microscopic images showed a highly structured bigel network with nanoemulsion droplets dispersed within the bigel network. Additionally, bigels exhibited pseudoplastic flow and viscoelastic properties. A complete drug release was achieved after 4-5 h. The in vitro and ex vivo antimicrobial studies revealed that bigels exhibited antimicrobial activity against different bacterial strains. Moreover, stability studies showed that the rheological properties and physical and chemical stability varied based on the bigel composition over three months. Therefore, the physicochemical and rheological properties, drug release rate, and antimicrobial activity of Type I bigels could be modified by altering the OL to WH ratio and the phase in which the nanoemulsion dispersed in.

Polyphenols: Natural Preservatives with Promising Applications in Food, Cosmetics and Pharma Industries; Problems and Toxicity Associated with Synthetic Preservatives; Impact of Misleading Advertisements; Recent Trends in Preservation and Legislation

The global market of food, cosmetics, and pharmaceutical products requires continuous tracking of harmful ingredients and microbial contamination for the sake of the safety of both products and consumers as these products greatly dominate the consumer's health, directly or indirectly. The existence, survival, and growth of microorganisms in the product may lead to physicochemical degradation or spoilage and may infect the consumer at another end. It has become a challenge for industries to produce a product that is safe, self-stable, and has high nutritional value, as many factors such as physical, chemical, enzymatic, or microbial activities are responsible for causing spoilage to the product within the due course of time. Thus, preservatives are added to retain the virtue of the product to ensure its safety for the consumer. Nowadays, the use of synthetic/artificial preservatives has become common and has not been widely accepted by consumers as they are aware of the fact that exposure to preservatives can lead to adverse effects on health, which is a major area of concern for researchers. Naturally occurring phenolic compounds appear to be extensively used as bio-preservatives to prolong the shelf life of the finished product. Based on the convincing shreds of evidence reported in the literature, it is suggested that phenolic compounds and their derivatives have massive potential to be investigated for the development of new moieties and are proven to be promising drug molecules. The objective of this article is to provide an overview of the significant role of phenolic compounds and their derivatives in the preservation of perishable products from microbial attack due to their exclusive antioxidant and free radical scavenging properties and the problems associated with the use of synthetic preservatives in pharmaceutical products. This article also analyzes the recent trends in preservation along with technical norms that regulate the food, cosmetic, and pharmaceutical products in the developing countries.

Oil-Based Sanitization in Low-Moisture Environments: Delivery of Acetic Acid with Water-in-Oil Emulsions

Contamination with Salmonella spp. and Listeria monocytogenes is concerning across low-moisture food (LMF)-processing environments due to the pronounced survival of these organisms under dry conditions. This study treated desiccated bacteria with acetic acid delivered by oil with and without water-in-oil (W/O) emulsion. The influences of cellular desiccation, emulsion water concentration, water activity (aw), and treatment temperature were investigated. Acetic acid dissolved in oil (i.e., acidified oil) showed low levels of antimicrobial efficacy. After treatment with acidified oil (200 mM acetic acid at 22°C for 30 min), Salmonella enterica serovar Enteritidis phage type 30 cells desiccated to 75% equilibrium relative humidity (ERH) and 33% ERH were reduced by 0.69 and 0.05 log CFU/coupon, respectively. The dispersion of a low level of water (≥0.3%, vol/vol) within the acidified oil with the surfactant (i.e., acidified W/O emulsion) significantly enhanced the antimicrobial efficacy. After treatment with the acidified W/O emulsion (200 mM acetic acid at 22°C for 20 min), desiccated Salmonella (4-strain cocktail) and L. monocytogenes (3-strain cocktail) cells were reduced by >6.52 log most probable number (MPN)/coupon, regardless of the desiccation levels. Increased efficacy was observed with temperature elevation. Reduced efficacy was observed when glycerol was added to the aqueous phase of the emulsion to decrease the solution aw, indicating that the enhanced efficacy of the acidified W/O emulsion was associated with differential osmotic pressure. The antimicrobial mechanism may be due to the membrane disruption induced by acetic acid, in combination with the hypoosmotic stress provided by W/O emulsion, creating cellular lysis, as illustrated by electron micrographs. IMPORTANCE Aqueous-based cleaning and sanitation are undesirable in processing facilities that manufacture low-moisture foods such as peanut butter and chocolate. Alcohol-based sanitization is advantageous because it leaves no residue on the contact surface but requires the processing facility to close temporarily due to flammability. At >6.52 log kill of desiccated Salmonella and Listeria monocytogenes cells, the developed oil-based formulation has the potential to be an effective dry sanitation method.

Efficacy of acidified water-in-oil emulsions against desiccated Salmonella as a function of acid carbon chain-length and membrane viscosity

Sanitizing low-moisture food (LMF) processing equipment is challenging due to the increased heat resistance of Salmonella spp. in low-water activity (a_w) environments. Food-grade oils mixed with acetic acid have been shown effective against desiccated Salmonella. In this study, different hydrocarbon chain-length (C_n) organic acids were tested against desiccated Salmonella by using 1% v/v water-in-oil (W/O) emulsion as the delivery system for 200 mM acid. Fluorescence lifetime imaging microscopy (FLIM) was utilized with a BODIPY-based molecular rotor to evaluate membrane viscosity under environmental conditions such as desiccation and temperature elevation. Drying hydrated Salmonella cells to 75% equilibrium relative humidity (ERH) increased the membrane viscosity from 1,199 to 1,309 mPa·s (cP) at 22°C. Heating to 45°C decreased the membrane viscosity of hydrated cells from 1,199 to 1,082 mPa·s, and decreased that of the desiccated cells from 1,309 to 1,245 mPa·s. At both 22°C and 45°C, desiccated Salmonella was highly susceptible (>6.5 microbial log reduction (MLR) per stainless-steel coupon) to a 30-min treatment with the W/O emulsions formulated with short carbon chain acids (C_1-3). By comparison, the emulsion formulations with longer carbon chain acids (C_4-12) showed little to no MLR at 22°C, but achieved >6.5 MLR at 45°C. Based upon the decreased Salmonella membrane viscosity and the increased antimicrobial efficacy of C_4-12 W/O emulsions with increasing temperature, we propose that heating can make the membrane more fluid which may allow the longer carbon chain acids (C_4-12) to permeate or disrupt membrane structures.

A recombinant strain of Komagataeibacter xylinus ATCC 23770 for Production of Bacterial Cellulose from Mannose-Rich Resources

The development of bacterial cellulose (BC) industrialization has been seriously affected by its production. Mannose/mannan is an essential component in many biomass resources, but Komagataeibacter xylinus uses mannose in an ineffective way, resulting in waste. The aim of this study was to construct recombinant bacteria to use mannose-rich biomass efficiently as an alternative and inexpensive carbon source in place of the more commonly used glucose. This strategy aimed at modification of the mannose catabolic pathway via genetic engineering of K. xylinus ATCC 23770 strain through expression of mannose kinase and phosphomannose isomerase genes from the Escherichia coli K-12 strain. Recombinant and wild-type strains were cultured under conditions of glucose and mannose respectively as sole carbon sources. The fermentation process and physicochemical properties of BC were investigated in detail in the strains cultured in mannose media. The comparison showed that with mannose as the sole carbon source, the BC yield from the recombinant strain increased by 84%, and its tensile strength and elongation were increased 1.7 fold, while Young's modulus was increased 1.3 fold. The results demonstrated a successful improvement in BC yield and properties on mannose-based medium compared with the wild-type strain. Thus, the strategy of modifying the mannose catabolic pathway of K. xylinus is feasible and has significant potential in reducing the production costs for industrial production of BC from mannose-rich biomass.

Understanding the Streptomyces albulus response to low-pH stress at the interface of physiology and transcriptomics

Streptomyces albulus is a well-established cell factory for ε-poly-L-lysine (ε-PL) production. It has been reported that ε-PL biosynthesis is strictly regulated by pH and that ε-PL can accumulate at approximately pH 4.0, which is outside of the general pH range for natural product production by Streptomyces species. However, how S. albulus responds to low pH is not clear. In this study, we attempted to explore the response of S. albulus to low-pH stress at the physiological and global gene transcription levels. At the physiological level, S. albulus maintained intracellular pH homeostasis at ~pH 7.5, increased the unsaturated fatty acid ratio, extended the fatty acid chain length, enhanced ATP accumulation, increased H⁺-ATPase activity, and accumulated the basic amino acids L-lysine and L-arginine. At the global gene transcription level, carbohydrate metabolism, oxidative phosphorylation, macromolecule protection and repair, and the acid tolerance system were found to be involved in combating low-pH stress. Finally, we preliminarily evaluated the effect of the acid tolerance system and cell membrane fatty acid synthesis on low-pH tolerance via gene manipulation. This work provides new insight into the adaptation mechanism of Streptomyces to low-pH stress and a new opportunity for constructing robust S. albulus strains for ε-PL production. KEY POINTS: • S. albulus consistently remained pH _i at ~7.4 regardless of the environmental pH. • S. albulus combats low-pH stress by modulating lipid composition of cell membrane. • Overexpression of cfa in S. albulus could improve low-pH tolerance and ɛ-PL titer.

Towards Electrochemical Sensor Based on Molecularly Imprinted Polypyrrole for the Detection of Bacteria-Listeria monocytogenes

Detecting bacteria-Listeria monocytogenes-is an essential healthcare and food industry issue. The objective of the current study was to apply platinum (Pt) and screen-printed carbon (SPCE) electrodes modified by molecularly imprinted polymer (MIP) in the design of an electrochemical sensor for the detection of Listeria monocytogenes. A sequence of potential pulses was used to perform the electrochemical deposition of the non-imprinted polypyrrole (NIP-Ppy) layer and Listeria monocytogenes-imprinted polypyrrole (MIP-Ppy) layer over SPCE and Pt electrodes. The bacteria were removed by incubating Ppy-modified electrodes in different extraction solutions (sulphuric acid, acetic acid, L-lysine, and trypsin) to determine the most efficient solution for extraction and to obtain a more sensitive and repeatable design of the sensor. The performance of MIP-Ppy- and NIP-Ppy-modified electrodes was evaluated by pulsed amperometric detection (PAD). According to the results of this research, it can be assumed that the most effective MIP-Ppy/SPCE sensor can be designed by removing bacteria with the proteolytic enzyme trypsin. The LOD and LOQ of the MIP-Ppy/SPCE were 70 CFU/mL and 210 CFU/mL, respectively, with a linear range from 300 to 6700 CFU/mL.

Acidity drives volatile metabolites in the spontaneous fermentation of sesame flavor-type baijiu

Environmental factors play an important role in contributing to intricate compositional dynamics and volatile metabolites in food fermentation. However, our understanding of which and how environmental factors affect volatile metabolites during sesame flavor-type baijiu fermentation is poor. Here, we examined the effects of environmental factors on the bacterial and fungal community to determine how changes in representative factors impact the microbial structure, diversity, and volatile metabolites in three fermentations. Results showed that bacterial community (ANOSIM: R = 0.79, P = 0.001), fungal community (ANOSIM: R = 0.65, P = 0.001), and volatile metabolites (ANOSIM: R = 0.84, P = 0.001) were significantly different in three fermentations. Acidity, ethanol, and moisture negatively impacted bacterial composition and diversity (P < 0.05). The fungal diversity and structure were positively and significantly affected by acidity (path coefficient, b = 0.54 for diversity, b = 0.35 for structure, P < 0.05). The fungal community rather than the bacterial community was the strongest driver of volatile metabolites. Fungal structure and diversity were equally important for the composition and content of volatile metabolites (structure: b = 0.50, diversity: b = 0.56, P < 0.05). 66 % of variations in volatile metabolites could be explained. Altogether these results indicated that acidity strongly drove volatile metabolites by modulating fungal structure and diversity. This work provides insights into managing volatile metabolites by regulating initial acidity in sesame flavor-type baijiu fermentation.

Probiotic Lactobacillus Species and Their Biosurfactants Eliminate Acinetobacter baumannii Biofilm in Various Manners

Acinetobacter baumannii is a critical biofilm-forming pathogen that has presented great challenges in the clinic due to multidrug resistance. Thus, new methods of intervention are needed to control biofilm-associated infections. In this study, among three tested Lactobacillus species, Lactobacillus rhamnosus showed significant antimaturation and antiadherence effects against A. baumannii biofilm. Lactic acid (LA) and acetic acid (AA) were the most effective antibiofilm biosurfactants (BSs) produced by L. rhamnosus. This antibiofilm phenomenon produced by LA and AA was due to the strong bactericidal effect, which worked from very early time points, as determined by colony enumeration and confocal laser scanning microscope. The cell destruction of A. baumannii appeared in both the cell envelope and cytoplasm. A discontinuous cell envelope, the leakage of cell contents, and the increased extracellular activity of ATPase demonstrated the disruption of the cell membrane by LA and AA. These effects also demonstrated the occurrence of protein lysis. In addition, bacterial DNA interacted with and was damaged by LA and AA, resulting in significantly reduced expression of biofilm and DNA repair genes. The results highlight the possibility and importance of using probiotics in clinical prevention. Probiotics can be utilized as novel biocides to block and decrease biofilm formation and microbial contamination in medical equipment and during the treatment of infections. IMPORTANCE A. baumannii biofilm is a significant virulence factor that causes the biofilm colonization of invasive illnesses. Rising bacterial resistance to synthetic antimicrobials has prompted researchers to look at natural alternatives, such as probiotics and their derivatives. In this study, L. rhamnosus and its BSs (LA and AA) demonstrated remarkable antibiofilm and antimicrobial characteristics, with a significant inhibitory effect on A. baumannii. These effects were achieved by several mechanisms, including the disruption of the cell envelope membrane, protein lysis, reduced expression of biofilm-related genes, and destruction of bacterial DNA. The results provide support for the possibility of using probiotics and their derivatives in the clinical prevention and therapy of A. baumannii infections.

Metabolomic analysis of the effects of a mixed culture of Saccharomyces cerevisiae and Lactiplantibacillus plantarum on the physicochemical and quality characteristics of apple cider vinegar

Introduction

This study compared differences in physicochemical characteristics of the vinegar made by a mixed culture (MC) of Saccharomyces cerevisiae and Lactiplantibacillus plantarum and a pure culture (PC) of Saccharomyces cerevisiae.

Methods

The fermentation process was monitored, and metabolomics analysis by Liquid Chromagraphy-Mass Spectrometry (LC-MS) was applied to the compositional differences between PC and MC vinegars, combined with quantification of organic acids, amino acids and B vitamins.

Results

A total of 71 differential metabolites including amino acids, organic acids and carbohydrates, and six possible key metabolic pathways were identified. MC enhanced the malic acid utilization and pyruvate acid metabolism during fermentation, increasing substrate-level phosphorylation, and supplying more energy for cellular metabolism. Higher acidity at the beginning of acetic acid fermentation, resulting from lactic acid production by Lactiplantibacillus plantarum in MC, suppressed the cellular metabolism and growth of Acetobacter pasteurianus, but enhanced its alcohol metabolism and acetic acid production in MC. MC vinegar contained more vitamin B, total flavonoids, total organic acids, amino acids and had a higher antioxidant capacity. MC enhanced the volatile substances, particularly ethyl lactate, ethyl caprate and ethyl caproate, which contributed to a stronger fruity aroma.

Discussion

These results indicated the mixed culture in alcoholic fermentation can effectively enhance the flavor and quality of apple cider vinegar.

Journey of the Probiotic Bacteria: Survival of the Fittest

This review aims to bring a more general view of the technological and biological challenges regarding production and use of probiotic bacteria in promoting human health. After a brief description of the current concepts, the challenges for the production at an industrial level are presented from the physiology of the central metabolism to the ability to face the main forms of stress in the industrial process. Once produced, these cells are processed to be commercialized in suspension or dried forms or added to food matrices. At this stage, the maintenance of cell viability and vitality is of paramount for the quality of the product. Powder products requires the development of strategies that ensure the integrity of components and cellular functions that allow complete recovery of cells at the time of consumption. Finally, once consumed, probiotic cells must face a very powerful set of physicochemical mechanisms within the body, which include enzymes, antibacterial molecules and sudden changes in pH. Understanding the action of these agents and the induction of cellular tolerance mechanisms is fundamental for the selection of increasingly efficient strains in order to survive from production to colonization of the intestinal tract and to promote the desired health benefits.

Metabolic changes of the acetogen Clostridium sp. AWRP through adaptation to acetate challenge

In this study, we report the phenotypic changes that occurred in the acetogenic bacterium Clostridium sp. AWRP as a result of an adaptive laboratory evolution (ALE) under the acetate challenge. Acetate-adapted strain 46 T-a displayed acetate tolerance to acetate up to 10 g L-1 and increased ethanol production in small-scale cultures. The adapted strain showed a higher cell density than AWRP even without exogenous acetate supplementation. 46 T-a was shown to have reduced gas consumption rate and metabolite production. It was intriguing to note that 46 T-a, unlike AWRP, continued to consume H2 at low CO2 levels. Genome sequencing revealed that the adapted strain harbored three point mutations in the genes encoding an electron-bifurcating hydrogenase (Hyt) crucial for autotrophic growth in CO2 + H2, in addition to one in the dnaK gene. Transcriptome analysis revealed that most genes involved in the CO2-fixation Wood-Ljungdahl pathway and auxiliary pathways for energy conservation (e.g., Rnf complex, Nfn, etc.) were significantly down-regulated in 46 T-a. Several metabolic pathways involved in dissimilation of nucleosides and carbohydrates were significantly up-regulated in 46 T-a, indicating that 46 T-a evolved to utilize organic substrates rather than CO2 + H2. Further investigation into degeneration in carbon fixation of the acetate-adapted strain will provide practical implications for CO2 + H2 fermentation using acetogenic bacteria for long-term continuous fermentation.

Dynamics of Microbial Communities, Flavor, and Physicochemical Properties during Ziziphus jujube Vinegar Fermentation: Correlation between Microorganisms and Metabolites

Jujube pulp separated from Ziziphus jujube is often discarded after processing, resulting in a serious waste of resources and environmental pollution. Herein, Ziziphus jujube pulp was used as a raw material for vinegar fermentation. To investigate the dynamic distribution of microorganisms and flavor substances in ZJV, correlations between environmental variables (e.g., total acid, reducing sugar, temperature) and flavor substances (organic acids, amino acids, volatile substances) and microorganisms were analyzed. Physicochemical indicators (temperature, total acid, alcohol) were the main factors affecting ZJV fermentation. The middle and later stages of ZJV fermentation were the periods showing the largest accumulation of flavor substances. Organic acids (acetic acid, malic acid, citric acid, lactic acid), amino acids (Asp, Glu, Arg) and volatile substances (ethyl phenylacetate, phenethyl alcohol) were important odor-presenting substances in ZJV. In the bacterial community, the Operational Taxonomic Units (OTUs) with an average relative abundance of more than 10% in at least one fermentation stage were mainly Acetobacter, Lactobacillus and Saccharopolyspora, while it was Thermomyces in the fungal community. Pearson correlation coefficients showed that Penicillium, Lactobacillus and Acetobacter were the core microorganisms, implying that these microorganisms contributed to the flavor formation greatly in ZJV fermentation. This study reveals the correlation between physicochemical indexes and flavor substances and microorganisms in ZJV fermentation. The results of the study can provide a theoretical basis for the development of the ZJV industry.

A two-stage process for the autotrophic and mixotrophic conversion of C1 gases into bacterial cellulose

Gas fermentation is a well-established process for the conversion of greenhouse gases from industrial wastes into valuable multi-carbon chemicals. Here, a two-stage process was developed to expand the product range of gas fermentation and synthesized the versatile biopolymer bacterial cellulose (BC). In the first stage, the acetogen Clostridium autoethanogenum was cultivated with H₂:CO:CO₂ and produced ethanol and acetate. In the second stage, BC-synthesizing Komagataeibacter sucrofermentans was grown in the spent medium from gas fermentation. K. sucrofermentans was able to produce BC autotrophically from gas-derived metabolites alone as well as mixotrophically with the addition of exogenous glucose. In these circumstances, 1.31 g/L BC was synthesized with a major energetic contribution from C1 gas fermentation products. Mixotrophic BC characterization reveals unique properties including augmented mechanical strength, porosity, and crystallinity. This proof-of-concept process demonstrates that BC can be produced from gases and holds good potential for the efficient conversion of C1 wastes.

RNA-Seq transcriptomic analysis reveals gene expression profiles of acetic acid bacteria under high-acidity submerged industrial fermentation process

Acetic acid bacteria (AAB) are Gram-negative obligate aerobics in Acetobacteraceae family. Producing acetic acid and brewing vinegars are one of the most important industrial applications of AAB, attributed to their outstanding ability to tolerate the corresponding stresses. Several unique acid resistance (AR) mechanisms in AAB have been revealed previously. However, their overall AR strategies are still less-comprehensively clarified. Consequently, omics analysis was widely performed for a better understanding of this field. Among them, transcriptome has recently obtained more and more attention. However, most currently reported transcriptomic studies were conducted under lab conditions and even in low-acidity environment, which may be unable to completely reflect the conditions that AAB confront under industrialized vinegar-brewing processes. In this study, we performed an RNA-Seq transcriptomic analysis concerning AAB’s AR mechanisms during a continuous and periodical industrial submerged vinegar fermentation process, where a single AAB strain performed the fermentation and the acetic acid concentration fluctuated between ~8% and ~12%, the highest acidity as far we know for transcriptomic studies. Samples were directly taken from the initial (CK), mid, and final stages of the same period of the on-going fermentation. 16S rRNA sequence analysis indicated the participation of Komagataeibacter europaeus in the fermentation. Transcriptomic results demonstrated that more genes were downregulated than upregulated at both mid and final stages. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrich analysis reflected that the upregulated genes mainly carried out tricarboxylic acid cycle and oxidative phosphorylation processes, probably implying a considerable role of acetic acid overoxidation in AR during fermentation. Besides, upregulation of riboflavin biosynthesis pathway and two NAD⁺-dependent succinate-semialdehyde dehydrogenase-coding genes suggested a critical role of succinate oxidation in AR. Meanwhile, downregulated genes were mainly ribosomal protein-coding ones, reflecting that the adverse impact on ribosomes initiates at the transcription level. However, it is ambiguous whether the downregulation is good for stress responding or it actually reflects the stress. Furthermore, we also assumed that the fermentation stages may have a greater effect on gene expression than acidity. Additionally, it is possible that some physiological alterations would affect the AR to a larger extent than changes in gene expression, which suggests the combination of molecular biology and physiology research will provide deeper insight into the AR mechanisms in AAB.

Screening and Characterization of New Acetobacter fabarum and Acetobacter pasteurianus Strains with High Ethanol−Thermo Tolerance and the Optimization of Acetic Acid Production

The production of vinegar on an industrial scale from different raw materials is subject to constraints, notably the low tolerance of acetic acid bacteria (AAB) to high temperatures and high ethanol concentrations. In this study, we used 25 samples of different fruits from seven Moroccan biotopes with arid and semi-arid environmental conditions as a basic substrate to isolate thermo- and ethanol-tolerant AAB strains. The isolation and morphological, biochemical and metabolic characterization of these bacteria allowed us to isolate a total number of 400 strains with characters similar to AAB, of which six strains (FAGD1, FAGD10, FAGD18 and GCM2, GCM4, GCM15) were found to be mobile and immobile Gram-negative bacteria with ellipsoidal rod-shaped colonies that clustered in pairs and in isolated chains. These strains are capable of producing acetic acid from ethanol, growing on peptone and oxidizing acetate to CO2 and H2O. Strains FAGD1, FAGD10 and FAGD18 show negative growth on YPG medium containing D-glucose > 30%, while strains GCM2, GCM4 and GCM15 show positive growth. These six strains stand out on CARR indicator medium as isolates of the genus Acetobacter ssp. Analysis of 16S rDNA gene sequencing allowed us to differentiate these strains as Acetobacter fabarum and Acetobacter pasteurianus. The study of the tolerance of these six isolates towards pH showed that most of the six strains are unable to grow at pH 3 and pH 9, with an ideal pH of 5. The behavior of the six strains at different concentrations of ethanol shows an optimal production of acetic acid after incubation at concentrations between 6% and 8% (v/v) of ethanol. All six strains tolerated an ethanol concentration of 16% (v/v). The resistance of the strains to acetic acid differs between the species of AAB. The optimum acetic acid production is obtained at a concentration of 1% (v/v) for the strains of FAGD1, FAGD10 and FAGD18, and 3% (v/v) for GCM2, GCM4 and GCM15. These strains are able to tolerate an acetic acid concentration of up to 6% (v/v). The production kinetics of the six strains show the highest levels of growth and acetic acid production at 30 °C. This rate of growth and acetic acid production is high at 35 °C, 37 °C and 40 °C. Above 40 °C, the production of acid is reduced. All six strains continue to produce acetic acid, even at high temperatures up to 48 °C. These strains can be used in the vinegar production industry to minimize the load on cooling systems, especially in countries with high summer temperatures.

Effects of Cellulase, Lactobacillus plantarum, and Sucrose on Fermentation Parameters, Chemical Composition, and Bacterial Community of Hybrid Pennisetum Silage

Hybrid Pennisetum (HP) is a perennial herb with a high yield and high quality, which makes it valuable for research as feed for herbivores. In order to make better use of hybrid Pennisetum as feed, this study studied the effects of cellulase (CE), Lactobacillus plantarum (LP), sucrose (SU), and their mixtures on fermentation parameters, chemical composition, and the bacterial community of hybrid Pennisetum silage. The experiment was divided into 7 treatments, silage treatment, and its abbreviation: CON (control group), CE (100 U/g FM cellulase), LP (1 × 106 cfu/g FM Lactobacillus plantarum), SU (1% FM sucrose), CE+LP (100 U/g FM cellulase + 1 × 106 cfu/g FM Lactobacillus plantarum), CE+SU (100 U/g FM cellulase + 1% FM sucrose), and LP+SU (1 × 106 cfu/g FM Lactobacillus plantarum + 1% FM sucrose). The silage bag was opened on the 60th day of ensilage for subsequent determination. The addition of CE and LP increased lactic acid content (p > 0.05). The pH and acetic acid of CE and LP were lower than CON (p < 0.05), and the crude protein content of CE was higher than CON. Cellulase and Lactobacillus plantarum can improve the quality of hybrid Pennisetum silage. Compared with Lactobacillus plantarum and sucrose, cellulase has better nutrition preservation and the ability to inhibit protein hydrolysis. 16S rRNA analysis showed that the dominant phyla were Fimicutes and Proteobacteria, and the dominant genera were Lactobacillus and Weissella. The changes in fermentation parameters and chemical components of hybrid Pennisetum silage caused by cellulase, Lactobacillus plantarum, sucrose, and their mixture may be the result of bacterial community changes.

A Snapshot of Microbial Succession and Volatile Compound Dynamics in Flat Peach Wine During Spontaneous Fermentation

Flat peaches possess characteristic flavors and are rich in nutrients. The fermentation of flat peaches to produce wine through complex biochemical reactions is an effective method to overcome their seasonal defects. Spontaneously fermented flat peach wine has plentiful and strong flavors, but the microbiota of fermentation are still unknown. In this study, the microbial succession and volatile compound dynamics of spontaneous fermentation in Xinjiang flat peach wine were investigated using high-throughput sequencing (HTS) and headspace solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) technology, respectively, to better understand the microbiota involved. Multivariate data analysis was used to predict the relationship between microorganisms and volatile chemicals. The results showed that Kazachstania, Pichia, Aspergillus, Fructobacillus, Leuconostoc, and Lactobacillus were the dominant genera during the spontaneous fermentation of flat peach wine. Furthermore, ethyl hexanoate, 3-hexen-1-yl acetate, ethyl caprate, ethyl caprylate, phenethyl acetate, ethanol, γ-decalactone, decanal, 1-hexanoic acid, and octanoic acid endued flat peach wine with a strong fruity and fatty aroma. The core functional microbiota (primarily consisting of 11 bacterial and 14 fungal taxa) was strongly associated with the production of 27 volatile compounds in the spontaneously fermented flat peach wine, according to multivariate data analysis. Some alcohols and esters were positively linked with the presence of Kazachstania and Pichia. Meanwhile, the presence of Fructobacillus, Leuconostoc, Lactobacillus, and Weissella was significantly correlated with 2-non-anol, ethanol, 3-methyl-1-butanol, octyl formate, isoamyl lactate, and ethyl lactate. This snapshot of microbial succession and volatile compound dynamics provides insights into the microorganisms involved in flat peach wine fermentation and could guide the production of flat peach wine with desirable characteristics.

The Potential of Sequential Fermentations in Converting C1 Substrates to Higher-Value Products

Today production of (bulk) chemicals and fuels almost exclusively relies on petroleum-based sources, which are connected to greenhouse gas release, fueling climate change. This increases the urgence to develop alternative bio-based technologies and processes. Gaseous and liquid C1 compounds are available at low cost and often occur as waste streams. Acetogenic bacteria can directly use C1 compounds like CO, CO₂, formate or methanol anaerobically, converting them into acetate and ethanol for higher-value biotechnological products. However, these microorganisms possess strict energetic limitations, which in turn pose limitations to their potential for biotechnological applications. Moreover, efficient genetic tools for strain improvement are often missing. However, focusing on the metabolic abilities acetogens provide, they can prodigiously ease these technological disadvantages. Producing acetate and ethanol from C1 compounds can fuel via bio-based intermediates conversion into more energy-demanding, higher-value products, by deploying aerobic organisms that are able to grow with acetate/ethanol as carbon and energy source. Promising new approaches have become available combining these two fermentation steps in sequential approaches, either as separate fermentations or as integrated two-stage fermentation processes. This review aims at introducing, comparing, and evaluating the published approaches of sequential C1 fermentations, delivering a list of promising organisms for the individual fermentation steps and giving an overview of the existing broad spectrum of products based on acetate and ethanol. Understanding of these pioneering approaches allows collecting ideas for new products and may open avenues toward making full use of the technological potential of these concepts for establishment of a sustainable biotechnology.

Impact of Elevated Levels of Dissolved CO2 on Performance and Proteome Response of an Industrial 2′-Fucosyllactose Producing Escherichia coli Strain

Large-scale microbial industrial fermentations have significantly higher absolute pressure and dissolved CO₂ concentrations than otherwise comparable laboratory-scale processes. Yet the effect of increased dissolved CO₂ (dCO₂) levels is rarely addressed in the literature. In the current work, we have investigated the impact of industrial levels of dCO₂ (measured as the partial pressure of CO₂, pCO₂) in an Escherichia coli-based fed-batch process producing the human milk oligosaccharide 2′-fucosyllactose (2′-FL). The study evaluated the effect of high pCO₂ levels in both carbon-limited (C-limited) and carbon/nitrogen-limited (C/N-limited) fed-batch processes. High-cell density cultures were sparged with 10%, 15%, 20%, or 30% CO₂ in the inlet air to cover and exceed the levels observed in the industrial scale process. While the 10% enrichment was estimated to achieve similar or higher pCO₂ levels as the large-scale fermentation it did not impact the performance of the process. The product and biomass yields started being affected above 15% CO₂ enrichment, while 30% impaired the cultures completely. Quantitative proteomics analysis of the C-limited process showed that 15% CO₂ enrichment affected the culture on the protein level, but to a much smaller degree than expected. A more significant impact was seen in the dual C/N limited process, which likely stemmed from the effect pCO₂ had on nitrogen availability. The results demonstrated that microbial cultures can be seriously affected by elevated CO₂ levels, albeit at higher levels than expected.

Adaptive Laboratory Evolution of Halomonas bluephagenesis Enhances Acetate Tolerance and Utilization to Produce Poly(3-hydroxybutyrate)

Acetate is a promising economical and sustainable carbon source for bioproduction, but it is also a known cell-growth inhibitor. In this study, adaptive laboratory evolution (ALE) with acetate as selective pressure was applied to Halomonas bluephagenesis TD1.0, a fast-growing and contamination-resistant halophilic bacterium that naturally accumulates poly(3-hydroxybutyrate) (PHB). After 71 transfers, the evolved strain, B71, was isolated, which not only showed better fitness (in terms of tolerance and utilization rate) to high concentrations of acetate but also produced a higher PHB titer compared with the parental strain TD1.0. Subsequently, overexpression of acetyl-CoA synthetase (ACS) in B71 resulted in a further increase in acetate utilization but a decrease in PHB production. Through whole-genome resequencing, it was speculated that genetic mutations (single-nucleotide variation (SNV) in phaB, mdh, and the upstream of OmpA, and insertion of TolA) in B71 might contribute to its improved acetate adaptability and PHB production. Finally, in a 5 L bioreactor with intermittent feeding of acetic acid, B71 was able to produce 49.79 g/L PHB and 70.01 g/L dry cell mass, which were 147.2% and 82.32% higher than those of TD1.0, respectively. These results highlight that ALE provides a reliable method to harness H. bluephagenesis to metabolize acetate for the production of PHB or other high-value chemicals more efficiently.