ORP control for boosting ethanol productivity in gas fermentation systems and dynamics of redox cofactor NADH/NAD+ under oxidative stress

Impact of kdcA, pdhD, and codY gene regulation in Lactococcus lactis 408 on 3-methylbutanal formation during cheddar cheese ripening

3-Methylbutanal, a key volatile compound contributing to the nutty flavor of cheese, was primarily produced through the microbial catabolism of leucine. This study focused on the metabolic pathway of 3-methylbutanal at the genetic level during the ripening of Cheddar cheese. The influence of key genes (kdcA, pdhD, and codY) in Lactococcus lactis 408, a specifically selected adjunct culture, on the production of 3-methylbutanal was evaluated. Over a 14-day ripening period, a minor difference in leucine production was observed among different samples with adjunct culture, while alterations in the genes kdcA and pdhD, which were overexpressed in the strain, led to a decreased concentration of α-ketoisocaproate. Utilizing headspace solid-phase microextraction coupled with gas chromatography-flame ionization detection, a reduction was observed in 3-methylbutanal levels as ripening progressed. However, cheese fermented with the codY knockout strain displayed the highest level of 3-methylbutanal at both 0.5-day and 28-day ripening milestones. Further analysis using an Ag/AgCl electrode to assess the redox environment revealed that the higher redox potential in the codY knockout strain was instrumental in retaining elevated levels of 3-methylbutanal. These findings underscored the critical role of genetic factors in the flavor development of cheese and offered promising targets for enhancing flavor profiles in dairy products through biotechnological interventions.

Biological co-reduction of Perchlorate and Nitrate in wastewater: Insights into the Competitive Inhibition Mechanisms in UASB Reactors

The pollution caused by wastewater with high perchlorate concentrations should not be underestimated. Efficient biodegradation is a promising treatment method. Nitrate, which often coexists with perchlorate in wastewater, has a great influence on its degradation. Therefore, in-depth studies on the combined degradation mechanisms of perchlorate and nitrate under coexisting conditions are essential. This study developed two heterotrophic up-flow anaerobic sludge blanket (UASB) reactors. In R1, perchlorate was efficiently removed, with a load of 927 ± 7.72 gClO4-/(m3·d), and removal efficiency exceeded 99.4%. In R2, perchlorate and nitrate were removed simultaneously, with loadings of 927 ± 3.52 gClO4-/(m3·d) and 81 ± 7.25 gNO3--N/(m3·d), respectively. Removal efficiencies were 95.9 ± 3.24% for perchlorate and 99.8 ± 0.09% for nitrate. A modified Monod competition model indicated that nitrate concentration exerts a more significant inhibitory effect at nitrate-to-perchlorate concentration ratios of 1:1 or higher. Batch experiments identified the optimal CH3COO-: ClO4-: NO3--N molar ratio as 5.4:1:3.6 and the ideal environmental ORP as -200 ± 20 mV for co-removal of perchlorate and nitrate. Metagenomic analysis revealed the dynamics of microbial communities and functional genes associated with perchlorate and nitrate reduction. Nitrate presence regulates the abundance and activity of NapC and cyt c transporter enzymes, which indirectly weaken the perchlorate electron transport pathway and directly affect terminal electron receptor coupling efficiency. This study provided valuable insights for optimizing biological treatment strategies for wastewater contaminated with perchlorate and nitrate.

Development and in-vitro assessment of novel oxygen-releasing feed additives to reduce enteric ruminant methane emissions

Ruminant livestock contribute significantly to global methane production and mitigation of which is of utmost importance. Feed additives represent a cost-effective means of achieving this. A potential target for such additives is rumen Oxidative Reduction Potential (ORP), a parameter which influences CH4 production rates, with methanogenesis occurring optimally at ORPs below -300 mV. Thus, a controlled elevation of rumen ORP represents a potentially benign means of methanogen suppression. This research involved assessing a range of oxygen-releasing compounds for their ability to increase rumen ORP and inhibit methanogenesis, using the in-vitro rumen simulation technique (RUSITEC). Seven potential CH4 inhibitors were tested in a 21-day trial monitoring biogas volume, CH4 content, ORP, digestibility, ammonia, and volatile fatty acids concentration. The additives evaluated included: liquid peroxide (H2O2) and urea hydrogen peroxide (UHP), as well as slower reacting species (calcium and magnesium peroxide), in addition to encapsulated liquid H2O2 for controlled, slow release. Consistent CH4 reductions of >50 % were observed from all additives. Reduced neutral detergent fibre (NDF) digestibility and a reduction in total volatile fatty acids (VFAs) was observed for some treatments, but MgO2 and encapsulated H2O2 reduced CH4 volume by 62 % and 58 %, respectively, and had no detrimental effects on digestibility (p > 0.05) or on VFA production. Ex-situ ORP measurements demonstrated significant increases in ORP upon addition of the additives, with MgO2 and encapsulated H2O2 inducing a more moderate effect suggesting a controlled additive release was achieved with the slow-release format of encapsulated liquid H2O2. Thus, potential slow-release forms deemed suitable to progress to bolus or pellet format in-vivo were identified and could enable a longer-lasting suppression of methanogens within the rumen, facilitating application in both intensive and pasture-based production systems.

Evaluating the impact of redox potential on the growth capacity of anaerobic gut fungi

Anaerobic gut fungi (AGF, Neocallimastigomycota) inhabit the alimentary tract of herbivores. Although strict anaerobes, studies have suggested their capacity to retain viability after various durations of air exposure. It is currently unclear whether AGF can actively grow, and not merely survive, in redox potentials (Eh) higher than those encountered in the herbivorous gut. We evaluated the growth of two AGF strains (Orpinomyces joyonii and Testudinimyces gracilis) at various Eh levels, achieved by manipulating the concentrations of reductant (cysteine hydrochloride) in culture media. Both strains exhibited robust and sustainable growth at negative Eh (-50 mV or below). However, growth in the absence of cysteine hydrochloride (Eh value around +50 mV) was possible only for O. joyonii and only for one subcultivation. The capacity to grow at +50 mV was further confirmed in four additional taxa (Pecoramyces ruminatium, Anaeromyces mucronatus, Aklioshbmyces papillarum, and Piromyces communis), while two (Aestipascuomyces dupliciliberans and Capellomyces foraminis) failed to grow under these conditions. Our results establish the ability of AGF to grow at redox potential values higher than those encountered in their natural habitats. Such capability could contribute to efficient AGF dispersal and horizontal transmission between hosts, and could have important implications for industrial applications of AGF.

Effect of antibiotics on the performance of moving bed biofilm reactor for simultaneous removal of nitrogen, phosphorus and copper(II) from aquaculture wastewater

Co-existence of NO3--N, antibiotics, phosphorus (P), and Cu2+ in aquaculture wastewater has been frequently detected, but simultaneous removal and relationship between enzyme and pollutants removal are far from satisfactory. In this study, simultaneous removal of NO3--N, P, antibiotics, and Cu2+ by moving bed biofilm reactor (MBBR) was established. About 95.51 ± 3.40% of NO3--N, 61.24 ± 3.51% of COD, 18.74 ± 1.05% of TP, 88% of Cu2+ were removed synchronously in stage I, and antibiotics removal in stages I-IV was 73.00 ± 1.32%, 79.53 ± 0.88%, 51.07 ± 3.99%, and 33.59 ± 2.73% for tetracycline (TEC), oxytetracycline (OTC), chlortetracycline hydrochloride (CTC), sulfamethoxazole (SMX), respectively. The removal kinetics and toxicity of MBBR effluent were examined, indicating that the first order kinetic model could better reflect the removal of NO3--N, TN, and antibiotics. Co-existence of multiple antibiotics and Cu2+ was the most toxicity to E. coli growth. Key enzyme activity, reactive oxygen species (ROS) level, and its relationship with TN removal were investigated. The results showed that enzymes activities were significantly different under the co-existence of antibiotics and Cu2+. Meanwhile, different components of biofilm were extracted and separated, and enzymatic and non-enzymatic effects of biofilm were evaluated. The results showed that 70.00%- 94.73% of Cu2+ was removed by extracellular enzyme in stages I-V, and Cu2+ removal was mainly due to the action of extracellular enzyme. Additionally, microbial community of biofilm was assessed, showing that Proteobacteria, Bacteroidetes, and Gemmatimonadetes played an important role in the removal of NO3--N, Cu2+, and antibiotics at the phylum level. Finally, chemical bonds of attached and detached biofilm were characterized by X-ray photoelectron spectroscopy (XPS), and effect of nitrogen (N) and P was proposed under the co-existence of antibiotics and Cu2+. This study provides a theoretical basis for further exploring the bioremediation of NO3--N, Cu2+, and antibiotics in aquaculture wastewater.

Unexpected metabolic rewiring of CO2 fixation in H2-mediated materials-biology hybrids

A hybrid approach combining water-splitting electrochemistry and H2-oxidizing, CO2-fixing microorganisms offers a viable solution for producing value-added chemicals from sunlight, water, and air. The classic wisdom without thorough examination to date assumes that the electrochemistry in such a H2-mediated process is innocent of altering microbial behavior. Here, we report unexpected metabolic rewiring induced by water-splitting electrochemistry in H2-oxidizing acetogenic bacterium Sporomusa ovata that challenges such a classic view. We found that the planktonic S. ovata is more efficient in utilizing reducing equivalent for ATP generation in the materials-biology hybrids than cells grown with H2 supply, supported by our metabolomic and proteomic studies. The efficiency of utilizing reducing equivalents and fixing CO2 into acetate has increased from less than 80% of chemoautotrophy to more than 95% under electroautotrophic conditions. These observations unravel previously underappreciated materials' impact on microbial metabolism in seemingly simply H2-mediated charge transfer between biotic and abiotic components. Such a deeper understanding of the materials-biology interface will foster advanced design of hybrid systems for sustainable chemical transformation.

Understanding the effect of temperature downshift on CHO cell growth, antibody titer and product quality by intracellular metabolite profiling and in vivo monitoring of redox state

The strategy of temperature downshift has been widely used in the biopharmaceutical industry to improve antibody production and cell-specific production rate (qp ) with Chinese hamster ovary cells (CHO). However, the mechanism of temperature-induced metabolic rearrangement, especially important intracellular metabolic events, remains poorly understood. In this work, in order to explore the mechanisms of temperature-induced cell metabolism, we systematically assessed the differences in cell growth, antibody expression, and antibody quality between high-producing (HP) and low-producing (LP) CHO cell lines under both constant temperature (37°C) and temperature downshift (37°C→33°C) settings during fed-batch culture. Although the results showed that low-temperature culture during the late phase of exponential cell growth significantly reduced the maximum viable cell density (p < 0.05) and induced cell cycle arrest in the G0/G1 phase, this temperature downshift led to a higher cellular viability and increased antibody titer by 48% and 28% in HP and LP CHO cell cultures, respectively (p < 0.001), and favored antibody quality reflected in reduced charge heterogeneity and molecular size heterogeneity. Combined extra- and intra-cellular metabolomics analyses revealed that temperature downshift significantly downregulated intracellular glycolytic and lipid metabolic pathways while upregulated tricarboxylic acid (TCA) cycle, and particularly featured upregulated glutathione metabolic pathways. Interestingly, all these metabolic pathways were closely associated with the maintenance of intracellular redox state and oxidative stress-alleviating strategies. To experimentally address this, we developed two high-performance fluorescent biosensors, denoted SoNar and iNap1, for real-time monitoring of intracellular nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide + hydrogen (NAD+ /NADH) ratio and nicotinamide adenine dinucleotide phosphate (NADPH) amount, respectively. Consistent with such metabolic rearrangements, the results showed that temperature downshift decreased the intracellular NAD+ /NADH ratio, which might be ascribed to the re-consumption of lactate, and increased the intracellular NADPH amount (p < 0.01) to scavenge intracellular reactive oxygen species (ROS) induced by the increased metabolic requirements for high-level expression of antibody. Collectively, this study provides a metabolic map of cellular metabolic rearrangement induced by temperature downshift and demonstrates the feasibility of real-time fluorescent biosensors for biological processes, thus potentially providing a new strategy for dynamic optimization of antibody production processes.

Antarctic Sphingomonas sp. So64.6b showed evolutive divergence within its genus, including new biosynthetic gene clusters

Introduction

The antibiotic crisis is a major human health problem. Bioprospecting screenings suggest that proteobacteria and other extremophile microorganisms have biosynthetic potential for the production novel antimicrobial compounds. An Antarctic Sphingomonas strain (So64.6b) previously showed interesting antibiotic activity and elicitation response, then a relationship between environmental adaptations and its biosynthetic potential was hypothesized. We aimed to determine the genomic characteristics in So64.6b strain related to evolutive traits for the adaptation to the Antarctic environment that could lead to its diversity of potentially novel antibiotic metabolites.

Methods

The complete genome sequence of the Antarctic strain was obtained and mined for Biosynthetic Gene Clusters (BGCs) and other unique genes related to adaptation to extreme environments. Comparative genome analysis based on multi-locus phylogenomics, BGC phylogeny, and pangenomics were conducted within the closest genus, aiming to determine the taxonomic affiliation and differential characteristics of the Antarctic strain.

Results and discussion

The Antarctic strain So64.6b showed a closest identity with Sphingomonas alpina, however containing a significant genomic difference of ortholog cluster related to degradation multiple pollutants. Strain So64.6b had a total of six BGC, which were predicted with low to no similarity with other reported clusters; three were associated with potential novel antibiotic compounds using ARTS tool. Phylogenetic and synteny analysis of a common BGC showed great diversity between Sphingomonas genus but grouping in clades according to similar isolation environments, suggesting an evolution of BGCs that could be linked to the specific ecosystems. Comparative genomic analysis also showed that Sphingomonas species isolated from extreme environments had the greatest number of predicted BGCs and a higher percentage of genetic content devoted to BGCs than the isolates from mesophilic environments. In addition, some extreme-exclusive clusters were found related to oxidative and thermal stress adaptations, while pangenome analysis showed unique resistance genes on the Antarctic strain included in genetic islands. Altogether, our results showed the unique genetic content on Antarctic strain Sphingomonas sp. So64.6, −a probable new species of this genetically divergent genus–, which could have potentially novel antibiotic compounds acquired to cope with Antarctic poly-extreme conditions.

A redox-based strategy to enhance propionic and butyric acid production during anaerobic fermentation

This study investigated the selective production of volatile fatty acids (VFAs) during anaerobic mixed-culture fermentation. The experiment used chicken manure (CM) as a potential substrate to produce high added-value propionic acid and butyric acid under an alkaline environment. The conversion of CM into selective VFAs depends highly on operational conditions such as pH and redox balance. Therefore, the current experiment is designed to employ amino acid addition and develop a redox balance control method to control the final VFA profile. This study showed that 0.2-5.0 % valine and threonine addition successfully enhanced propionic acid and butyric acid production during alkaline fermentation and hence decreased the proportion of acetic acid from 83 % to approximately 47 %. The oxidation-reduction potential (ORP) and redox cofactor ratio (NADH/NAD⁺) were measured to support the selective VFA production mechanism. The results obtained in this study bring extra value to the valorization of CM within the circular economy concept for selective value-added VFA production.