Metabolic flux and functional potential of microbial community in an acidogenic dynamic membrane bioreactor

Predicting metabolic pathways and microbial interactions in dark fermentation systems treating real cheese whey effluents

Dark fermentation of agro-industrial effluents is a promising way for waste valorization. However, understanding the complex microbial dynamics and metabolic interactions within the microbial communities remains challenging. This study investigates the microbial communities involved in continuous hydrogen production from cheese whey and fermented cheese whey using functional profiling with PICRUSt2. The analysis reveals the primary roles of key microbial genera. Lactobacillus dominates carbohydrate consumption and lactate production, while Clostridium sensu stricto 12 and Caproiciproducens are engaged in a competitive dynamic for lactate utilization. Clostridium sensu stricto 12 drives hydrogen production via electron bifurcation reactions, whereas Caproiciproducens may utilize alternative energy conservation mechanisms. The interaction between these genera is influenced by substrate availability and process conditions. This study highlights the utility of functional profiling in elucidating microbial interactions and metabolic pathways in dark fermentation. The findings emphasize the importance of understanding microbial interactions to optimize biohydrogen production processes.

The synergistic role of ozonation and hydrolysis acidification on the enhanced pre-treatment of high-strength refractory 2-butenal manufacture wastewater: Performance, metabolism, and mechanisms

Targeted removal of three key refractory toxic organic compounds (TOMs) in 2-butenal manufacturing wastewater (2-BMW) is critical for enhancing pre-treatment by hydrolysis acidification (HA). We investigated the pre-treatment of 2-BMW with HA, coupled with ozonation in this study. Our results indicated that the removal rate of these key TOMs and the detoxification rate reached almost 100% and 46.3%, respectively, by ozonation under only 0.099 mg O3/mg chemical oxygen demand (COD). The organic load rate (OLR) reached 10.25 ± 0.43 kg COD/m3·d, and the acidification degree (AD) and detoxification efficiency reached 56.0% and 98.3%, respectively, with enhancements of 35.1% and 55.2%, respectively, compared with HA alone. The removal rate of the three key TOMs was improved by > 75%. The degradation pathways of these key TOMs were ring cleavage and ester formation by ozonation, followed by fermentation and acid production by HA. Ultimately, the synergistic role of ozonation and HA was revealed. The preferential cleavage of these key TOMs by ozonation was achieved because of their high electron cloud density and multiple reaction sites, which generated more fermentation-friendly products. The fermentation and acid production reactions may be directly involved in these products. Functional bacteria and key metabolic pathways were also enhanced by ozonation.

Repercussion of extracellular polymeric removal by low-temperature calcium peroxide pretreatment on bacterial fragmentation for enhancing biohydrogen production

This study envisioned attaining the percipience of effective biohydrogen production from paper mill waste-activated sludge through low-temperature calcium peroxide-mediated bacterial pretreatment (TCP-BP). Floc dissociation with limited cell destruction was attained at a calcium peroxide dosage of 0.05 g/g suspended solids (SS) at 70 °C temperature. This TCP-BP method improves bacterial fragmentation, and very high SS solubilization was achieved at 42 h, with the solubilization and solid reduction of 18.6% and 14.1%, respectively. BP-only pretreatment shows lower solubilization efficiency of 9.4% than TCP-BP pretreatment due to the presence of flocs, which inhibit the enzymatic action during bacterial fragmentation. A biohydrogen test shows a high biohydrogen potential of 94.1 mL H₂/gCOD for the TCP-BP sample, which is higher than that of the BP-only and control samples. According to the findings, low-temperature calcium peroxide-mediated bacterial fragmentation is validated to be an efficient process for sludge degradation and biohydrogen production.

Base type determines the effects of nucleoside monophosphates on microalgae-bacteria symbiotic systems

Microalgae are promising sources of clean energy. Bioflocculation by cocultured bacteria is an effective way to harvest microalgae. As a key foundation for microorganisms, phosphorus is theoretically effective in shaping microalgae production and flocculation. In this study, the impacts of 23 nucleoside monophosphates on Auxenochlorella pyrenoidosa growth, lipid synthesis, and self-settlement and on the symbiotic bacterial system were investigated. Adenosine monophosphate was the most effective in enhancing microalgae development (2.14-3.16 × 10⁸ cells/mL) and lipid production (average 10.48%) and resulted in a low settling velocity. Samples were divided into two groups, purine and pyrimidine feeding, according to a random forest analysis (OOB = 0%, p < 0.001). Purine feeding resulted in the highest soluble extracellular protein and polysaccharide secretion (p < 0.01). KEGG ortholog count prediction of functional genes related to biofilm formation was conducted using PICRUSt2, and significant upregulation (FC ≥ 1.77, p < 0.05) of the extracellular polymeric substance formation functional group was observed in the adenosine and guanosine treatments. The symbiotic bacterial community structure differed substantially between purine- and pyrimidine-feeding systems. In summary, these results indicated that the effect of nucleoside monophosphates on the microalgae-bacteria system is determined by the base type (purine or pyrimidine) rather than the molecular structure (cyclic or noncyclic).

Inhibitory effect of acetic acid on dark-fermentative hydrogen production

This study examined the working mechanisms of acetic acid inhibition on dark fermentative hydrogen production. It was found that undissociated acetic acid (UAA) concentration was the critical factor in acetic acid inhibition. Hydrogen production activity decreased by 50 % and 90 % when UAA concentrations was 76.3 mg/L (1.27 mmol/L) and 686.7 mg/L (11.44 mmol/L), respectively. Dominant microbes were changed from genus Clostridium_sensu_stricto_1 to genus Inhella, Aquabacterium and Caulobacter under the stress of acetic acid inhibition. Functional enzyme analysis showed that acetic acid inhibited the hydrogen production by activating the lactate formation pathway when UAA concentration was below the inhibition threshold, while by impairing most hydrogen-producing pathways when UAA concentration was over the inhibition threshold. In brief, acetic acid inhibited the hydrogen production by altering the dominant microbial community and regulating the metabolic pathways, controlling the UAA concentration would be a good strategy to alleviate the acetic acid inhibition.

Dynamic change of bacterial diversity, metabolic pathways, and flavor during ripening of the Chinese fermented sausage

Chinese fermented sausage is a famous fermented meat product with a complex microbiota that has a potential impact on flavor and quality. In this study, Lactobacillus plantarum MSZ2 and Staphylococcus xylosus YCC3 were used as starter cultures to investigate the change in bacterial diversity, metabolic pathways, and flavor compounds during the ripening process of fermented sausages. High-throughput sequencing technology and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC/MS) were applied for characterizing the profiles of bacterial diversity, metabolic pathways, and flavor compounds in sausage samples on days 0, 6, and 12 during ripening. Results showed that Lactobacillus, Staphylococcus, Lactococcus, Leuconostoc, and Weissella were the most abundant bacterial genera found in the sausage samples during all stages of fermentation. Functional prediction reveals the abundance of 12 different metabolic pathways, the most important pathways are carbohydrate metabolism, nucleotide metabolism, lipid metabolism, and amino acid metabolism. A total of 63 volatile compounds were successfully identified in fermented sausage samples. Correlational analysis demonstrated that Staphylococcus and Leuconostoc were closely related to the formation of flavor compounds. Therefore, the present study may provide guidance for future use of microbiota to improve flavor, quality, and preservation of fermented sausages.

Shifts in rhizosphere microbial communities in Oplopanax elatus Nakai are related to soil chemical properties under different growth conditions

Plant growth environment plays an important role in shaping soil microbial communities. To understand the response of soil rhizosphere microbial communities in Oplopanax elatus Nakai plant to a changed growth conditions from natural habitation to cultivation after transplant. Here, a comparative study of soil chemical properties and microbial community using high-throughput sequencing was conducted under cultivated conditions (CT) and natural conditions (WT), in Changbai Mountain, Northeast of China. The results showed that rhizosphere soil in CT had higher pH and lower content of soil organic matter (SOM) and available nitrogen compared to WT. These changes influenced rhizosphere soil microbial communities, resulting in higher soil bacterial and fungi richness and diversity in CT soil, and increased the relative abundance of bacterial phyla Acidobacteria, Chloroflexi, Gemmatimonadetes, Firmicutes and Patescibacteria, and the fungi phyla Mortierellomycota and Zoopagomycota, while decreased bacterial phyla Actinobacteria, WPS-2, Gemmatimonadetes, and Verrucomicrobia, and the fungi phyla Ascomycota, and Basidiomycota. Redundancy analysis analysis indicated soil pH and SOM were the primarily environmental drivers in shaping the rhizosphere soil microbial community in O. elatus under varied growth conditions. Therefore, more attention on soil nutrition management especially organic fertilizer inputs should be paid in O. elatus cultivation.

Insights into the role of biochar on the acidogenic process and microbial pathways in a granular sulfate-reducing up-flow sludge bed reactor

In this study, the effect of biochar on sulfate reduction and anaerobic acidogenic process was explored in a granular sulfate-reducing up-flow sludge bed reactor in both long-term operation and batch tests. Both bioreactors had a high sulfate reduction efficiency of over 95% during the long-term operation, while the reactor with biochar addition showed higher sulfate reduction efficiency and stronger robustness against volatile fatty acids accumulation with a higher organic loading and sulfate loading rate. Batch tests showed that adding biochar significantly lessened the lag phase of the sulfate-reducing process, accelerated the adaption of acidogens, and facilitated both production and utilization of volatile fatty acids. The microbial pathways proved that biochar could regulate the acidification fermentation pathway and facilitate the enrichment of assimilative desulfurization bacteria. Overall, this study revealed that the acidogenic sulfate-reducing metabolic pathway could be enhanced by biochar, offering a potential application for effective sulfate-laden wastewater treatment.

Efficient removal of organic compounds from shale gas wastewater by coupled ozonation and moving-bed-biofilm submerged membrane bioreactor

Shale gas wastewater (SGW) with complex composition and high salinity needs an economical and efficient method of treatment with the main goal to remove organics. In this study, a coupled system consisting of ozonation and moving-bed-biofilm submerged membrane bioreactor (MBBF-SMBR) was comprehensively evaluated for SGW treatment and compared with a similar train comprising ozonation and submerged membrane bioreactor (SMBR) without addition of carriers attaching biofilm. The average removal rates of MBBF-SMBR were 77.8% for dissolved organic carbon (DOC) and 37.0% for total nitrogen (TN), higher than those observed in SMBR, namely, 73.9% for DOC and 18.6% for TN. The final total membrane resistance in SMBR was 40.1% higher than that in MBBF-SMBR. Some genera that specifically contribute to organic removal were identified. Enhanced gene allocation for membrane transport and nitrogen metabolism was found in MBBF-SMBR biofilm, implying that this system has significant industrial application potential for organics removal from SGW.

Akkermansia Muciniphila Potentiates the Antitumor Efficacy of FOLFOX in Colon Cancer

FOLFOX (oxaliplatin, fluorouracil and calcium folinate) is the first-line chemotherapy regimen for colon cancer therapy in the clinic. It provides superior efficacy than oxaliplatin alone, but the underlying mechanism remains unclear. In the present study, pharmacomicrobiomics integrated with metabolomics was conducted to uncover the role of the gut microbiome behind this. First, in vivo study demonstrated that FOLFOX exhibited better efficacy than oxaliplatin alone in colon cancer animal models. Second, 16S rDNA gene sequencing analysis showed that the abundance of Akkermansia muciniphila (A. muciniphila) remarkably increased in the FOLFOX treated individuals and positively correlated with the therapeutic effect. Third, further exploration confirmed A. muciniphila colonization significantly enhanced the anti-cancer efficacy of FOLFOX. Last, metabolomics analysis suggested dipeptides containing branched-chain amino acid (BCAA) might be responsible for gut bacteria mediated FOLFOX efficacy. In conclusion, our study revealed the key role of A. muciniphila in mediating FOLFOX efficacy, and manipulating A. muciniphila might serve as a novel strategy for colon cancer therapy.

Mechanisms of enhanced hydrogen production from sewage sludge by ferrous ion: Insights into functional genes and metabolic pathways

Hydrogen production from sewage sludge was studied in the presence of Fe²⁺. The results showed that the highest cumulative hydrogen production of 26 mL/100 mL was achieved with 600 mg/L Fe²⁺ supplementation, which was 2 times of the control test. In depth analysis of organics in liquid phase revealed that Fe²⁺ addition promoted sludge disintegration and protein degradation during fermentation process. Functions prediction by PICRUSt analysis indicated the effect of Fe²⁺ on microbial metabolism and functional genes expression. The results showed that the expression of hydrogen-producing functions, like ferredoxin hydrogenase and formate dehydrogenase was activated by Fe²⁺ supplementation, while the hydrogen-consuming metabolism, like methane metabolism and homoacetogenic metabolism was inhibited. Furthermore, Fe²⁺ addition could stimulate organics utilization. This study explored the effect of Fe²⁺ on functional genes abundance, revealing the mechanisms of enhanced hydrogen production by Fe²⁺ from the perspective of microbial metabolism.

State-of-the-art technologies for continuous high-rate biohydrogen production

Dark fermentation is a technically feasible technology for achieving carbon dioxide-free hydrogen production. This review presents the current findings on continuous hydrogen production using dark fermentation. Several operational strategies and reactor configurations have been suggested. The formation of attached mixed-culture microorganisms is a typical prerequisite for achieving high production rate, hydrogen yield, and resilience. To date, fixed-bed reactors and dynamic membrane bioreactors yielded higher biohydrogen performance than other configurations. The symbiosis between H₂-producing bacteria and biofilm-forming bacteria was essential to avoid washout and maintain the high loading rates and hydrogenic metabolic flux. Recent research has initiated a more in-depth comparison of microbial community changes during dark fermentation, primarily with computational science techniques based on 16S rRNA gene sequencing investigations. Future techno-economic analysis of dark fermentative biohydrogen production and perspectives on unraveling mitigation mechanisms induced by attached microorganisms in dark fermentation processes are further discussed.

High-rate mesophilic hydrogen production from food waste using hybrid immobilized microbiome

This study examined the feasibility of dark fermentative biohydrogen production from food waste using hybrid immobilization in mesophilic condition. Among four different organic loading rates (OLRs), the highest average hydrogen production rate (HPR) of 9.82 ± 0.30 L/L-d was found at an OLR of 74.7 g hexose/L-d, which was higher than reported values from particulate feedstock in mesophilic condition. The average hydrogen yield (HY) at the condition was 1.25 ± 0.04 mol H₂/mol hexose_consumed. Whereas the average HPR and HY at an OLR 80 g hexose/L-d were 5.82 ± 0.12 L/L-d and 0.64 ± 0.02 mol H₂/mol hexose_consumed, respectively. Metabolic flux analysis showed the low HY was concurrent with the highest propionic acid and homoacetogenis. Bacterial population was shift from Clostridium sp. to non-hydrogen producers including Bifidobacterium, Bacteriodes, Olsenella, Dysgonomonas, and Dialister sp.

Aerobic denitrifying bacterial communities drive nitrate removal: Performance, metabolic activity, dynamics and interactions of core species

Three novel mix-cultured aerobic denitrifying bacteria (Mix-CADB) consortia named D14, X21, and CL exhibited excellent total organic carbon (TOC) removal and aerobic denitrification capacities. The TOC and nitrate removal efficiencies were higher than 93.00% and 98.00%. The results of Biolog demonstrated that three communities displayed high carbon metabolic activity. nirS gene sequencing and ecological network model revealed that Pseudomonas stutzeri, Paracoccus sp., and Paracoccus denitrificans dominated in the D14, X21, and CL communities. The dynamics and co-existence of core species in communities drove the nutrient removal. Response surface methodology showed the predicted total nitrogen removal efficiency reached 99.43% for D14 community. The three Mix-CADB consortia have great potential for nitrogen-polluted aquatic water treatment because of their strong adaptability and removal performance. These results will provide new understanding of co-existence, interaction and dynamics of Mix-CADB consortia for nitrogen removal in nitrogen-polluted aquatic ecosystems.