Metaproteomic analysis of the relationship between microbial community phylogeny, function and metabolic activity during biohydrogen-methane coproduction under short-term hydrothermal pretreatment from food waste

Value addition through biohydrogen production and integrated processes from hydrothermal pretreatment of lignocellulosic biomass

Bioenergy production is the most sought-after topics at the crunch of energy demand, climate change and waste generation. In view of this, lignocellulosic biomass (LCB) rich in complex organic content has the potential to produce bioenergy in several forms following the pretreatment. Hydrothermal pretreatment that employs high temperatures and pressures is gaining momentum for organics recovery from LCB which can attain value-addition. Diverse bioprocesses such as dark fermentation, anaerobic digestion etc. can be utilized following the pretreatment of LCB which can result in biohydrogen and biomethane production. Besides, integration approaches for LCB utilization that enhance process efficiency and additional products such as biohythane production as well as application of solid residue obtained after LCB pretreatment were discussed. Importance of hydrothermal pretreatment as one of the suitable strategies for LCB utilization is emphasized suggesting its future potential in large scale energy recovery.

Microbiomes of biohydrogen production from dark fermentation of industrial wastes: current trends, advanced tools and future outlook

Biohydrogen production through dark fermentation is very attractive as a solution to help mitigate the effects of climate change, via cleaner bioenergy production. Dark fermentation is a process where organic substrates are converted into bioenergy, driven by a complex community of microorganisms of different functional guilds. Understanding of the microbiomes underpinning the fermentation of organic matter and conversion to hydrogen, and the interactions among various distinct trophic groups during the process, is critical in order to assist in the process optimisations. Research in biohydrogen production via dark fermentation is currently advancing rapidly, and various microbiology and molecular biology tools have been used to investigate the microbiomes. We reviewed here the different systems used and the production capacity, together with the diversity of the microbiomes used in the dark fermentation of industrial wastes, with a special emphasis on palm oil mill effluent (POME). The current challenges associated with biohydrogen production were also included. Then, we summarised and discussed the different molecular biology tools employed to investigate the intricacy of the microbial ecology associated with biohydrogen production. Finally, we included a section on the future outlook of how microbiome-based technologies and knowledge can be used effectively in biohydrogen production systems, in order to maximise the production output.

Evaluation of biochar addition and circulation control strengthening measures on efficiency and microecology of food waste treatment in anaerobic reactor

The process of strengthening an expanded granular sludge blanket (EGSB) reactor under ammonia nitrogen stress conditions and by adopting three strengthening measures, namely, opening the circulation (OC), adding modified biochar (MB), adding modified biochar along with opening the circulation (MBOC), to treat food waste was studied. When the ammonia nitrogen concentration of influent increased to 1200 mg/L, the removal rate of COD reduced to about 75%, while the removal rate of ammonia nitrogen was about 6%. The average COD removal rate of the anaerobic reactor in the last 5 days of each operating cycle i.e. OC, MB and MBOC, was 85.51%, 84.11% and 90.03%, respectively. At the 30th day of each treatment-OC, MB and MBOC, the protease content in the sludge was 44.61, 42.47, 46.24 NH₂-N (mg)/mg, respectively. and the content of coenzyme F₄₂₀ was 0.244, 0.217 and 0.267 mmol/g, respectively. Proteobacteria was the most abundant phylum in the stage I (OC), reaching 34.36%. It was accounted for 16.68% and 21.38%, respectively, in the stage II (MB) and stage III (MBOC). The dominant archaea in the three stages were Methanosaeta, whose abundance was 38.98% in stage I, which increased to 64.94% and 64.01% in stage II and III, respectively. Among the active carbohydrate enzymes, the gene abundance of Glycoside transferases in the MBOC stage was the largest among the three stages.

Microbial and functional characterization of an allochthonous consortium applied to hydrogen production from Citrus Peel Waste in batch reactor in optimized conditions

Energy recovery from lignocellulosic waste has been studied as an alternative to the problem of inappropriate waste disposal. The present study aimed at characterizing the microbial community and the functional activity of reactors applied to H₂ production through lignocellulosic waste fermentation in optimized conditions. The latter were identified by means of Rotational Central Composite Design (RCCD), applied to optimize allochthonous inoculum concentration (2.32-5.68 gTVS/L of granular anaerobic sludge), pH (4.32-7.68) and Citrus Peel Waste (CPW) concentration (1.55-28.45 g/L). After validation, the conditions identified for optimal H₂ production were 4 gSTV/L of allochthonous inoculum, 29.8 g/L of CPW (substrate) and initial pH of 8.98. In these conditions, 48.47 mmol/L of H₂ was obtained, which is 3.64 times higher than the concentration in unoptimized conditions (13.31 mmol H₂/L using 15 g/L of CPW, 2 gTVS/L of allochthonous inoculum, pH 7.0). Acetogenesis was the predominant pathway, and maximal concentrations of 3,731 mg/L of butyric acid and 3,516 mg/L of acetic acid were observed. Regarding the metataxonomic profile, Clostridium genus was dramatically favored in the optimized condition (79.78%) when compared to the allochthonous inoculum (0.43%). It was possible to identify several genes related to H₂ (i.e dehydrogenases) and volatile fatty acids (VFA) production and with cellulose degradation, especially some CAZymes from the classes Auxiliary Activities, Glycoside Hydrolases and Glycosyl Transferase. By means of differential gene expression it was observed that cellulose degradation and acetic acid production pathways were overabundant in samples from the optimized reactors, highlighting endo-β-1,4-glucanase/cellulose, endo-β-1,4-xylanase, β-glucosidase, β-mannosidase, cellulose β-1,4-cellobiosidase, cellobiohydrolase, and others, as main the functions.

Perspectives on microbial community in anaerobic digestion with emphasis on environmental parameters: A systematic review

This paper review is aiming to comprehensively identify and appraise the current available knowledge on microbial composition and microbial dynamics in anaerobic digestion with focus on the interconnections between operational parameters and microbial community. We systematically searched Scopus, Web of Science, pubmed and Embase (up to August 2019) with relative keywords to identify English-language studies published in peer-reviewed journals. The data and information on anaerobic reactor configurations, operational parameters such as pretreatment methods, temperature, trace elements, ammonia, organic loading rate, and feedstock composition and their association with the microbial community and microbial dynamics were extracted from eligible articles. Of 306 potential articles, 112 studies met the present review objectives and inclusion criteria. The results indicated that both aceticlastic and hydrogenotrophic methanogenesis are dominant in anaerobic digesters and their relative composition is depending on environmental conditions. However, hydrogenotrophic methanogens are more often observed in extreme conditions due to their higher robustness compared to aceticlastic methangoens. Firmicutes and Bacteroidetes phyla are most common fermentative bacteria of the acidogenic phase. These bacteria secrete lytic enzymes to degrade organic matters and are able to survive in extreme conditions and environments due to their spores. In addition, among archaea Methanosaeta, Methanobacterium, and Methanosarcinaceae are found at high relative abundance in anaerobic digesters operated with different operational parameters. Overall, understanding the shifts in microbial composition and diversity as results of operational parameters variation in anaerobic digestion process would improve the stability and process performance.

Rainfall Alters Permafrost Soil Redox Conditions, but Meta-Omics Show Divergent Microbial Community Responses by Tundra Type in the Arctic

Soil anoxia is common in the annually thawed surface (‘active’) layer of permafrost soils, particularly when soils are saturated, and supports anaerobic microbial metabolism and methane (CH4) production. Rainfall contributes to soil saturation, but can also introduce oxygen, causing soil oxidation and altering anoxic conditions. We simulated a rainfall event in soil mesocosms from two dominant tundra types, tussock tundra and wet sedge tundra, to test the impacts of rainfall-induced soil oxidation on microbial communities and their metabolic capacity for anaerobic CH4 production and aerobic respiration following soil oxidation. In both types, rainfall increased total soil O2 concentration, but in tussock tundra there was a 2.5-fold greater increase in soil O2 compared to wet sedge tundra due to differences in soil drainage. Metagenomic and metatranscriptomic analyses found divergent microbial responses to rainfall between tundra types. Active microbial taxa in the tussock tundra community, including bacteria and fungi, responded to rainfall with a decline in gene expression for anaerobic metabolism and a concurrent increase in gene expression for cellular growth. In contrast, the wet sedge tundra community showed no significant changes in microbial gene expression from anaerobic metabolism, fermentation, or methanogenesis following rainfall, despite an initial increase in soil O2 concentration. These results suggest that rainfall induces soil oxidation and enhances aerobic microbial respiration in tussock tundra communities but may not accumulate or remain in wet sedge tundra soils long enough to induce a community-wide shift from anaerobic metabolism. Thus, rainfall may serve only to maintain saturated soil conditions that promote CH4 production in low-lying wet sedge tundra soils across the Arctic.

Dibutyl phthalate contamination accelerates the uptake and metabolism of sugars by microbes in black soil

Dibutyl phthalate (DBP) is widely used as plasticizer and has been detected in the environment, posing a threat to animal health. However, the effects of DBP on agricultural microbiomes are not known. In this study, DBP levels in black soil were evaluated, and the impact of DBP contamination on the uptake and metabolism of sugars in microbes was assessed by glucose absorption tests, metaproteomics, metabolomics, enzyme activity assays and computational simulation analysis. The results indicated that DBP contamination accelerated glucose consumption and upregulated the expression of porins and periplasmic monosaccharide ATP-binding cassette (ABC) transporter solute-binding proteins (SBPs). DBP and its metabolic intermediates (carboxymuconate and butanol) may form a stable complex with sugar transporters and enhance the rigidity and stability of these proteins. Sugar metabolism resulting in the generation of ATP and reducing agent (NADPH), as well as the expression of some key enzymes (dehydrogenases) were also upregulated by DBP treatment. Moreover, a diverse bacterial community appears to utilize sugar, suggesting that there are widespread effects of DBP contamination on soil microbial ecosystems. The results of this study provide a theoretical basis for investigating the toxicological effects of DBP on microbes in black soil.

Enhancement of hydrogen production and energy recovery through electro-fermentation from the dark fermentation effluent of food waste

To enhance hydrogen production efficiency and energy recovery, a sequential dark fermentation and microbial electrochemical cell (MEC) process was evaluated for hydrogen production from food waste. The hydrogen production, electrochemical performance and microbial community dynamics were investigated during startup of the MEC that was inoculated with different sludges. Results suggest that biogas production rates and hydrogen proportions were 0.83 ​L/L d and 92.58%, respectively, using anaerobic digested sludge, which is higher than that of the anaerobic granular sludge (0.55 ​L/L d and 86.21%). The microbial community were predominated by bacterial genus Acetobacterium, Geobacter, Desulfovibrio, and archaeal genus Methanobrevibacter in electrode biofilms and the community structure was relatively stable both in anode and cathode. The sequential system obtained a 53.8% energy recovery rate and enhanced soluble chemical oxygen demand (sCOD) removal rate of 44.3%. This research demonstrated an important approach to utilize dark fermentation effluent to maximize the conversion of fermentation byproducts into hydrogen.

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Sequential dark fermentation and microbial electrolysis cell was evaluated.

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The best bio-electrochemical performance with anaerobic digested sludge in the microbial electrolysis cells startup.

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Acetobacterium, Geobacte and Methanobrevibacter were the dominant genera in electrode biofilms.

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53.8% energy recovery was achieved in the sequential electro-fermentation process.

Metaproteomics of Microbiota in Naturally Fermented Soybean Paste, Da-jiang

Da-jiang is a typical traditional fermented soybean product in China. At present, the proteins in da-jiang are needed to be explored. The composition and species of microbial proteins in traditional fermented da-jiang were analyzed by metaproteomics based on sodium dodecyl sulfonate-polyacrylamide gel electrophoresis (SDS-PAGE) and liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). The results showed that the number and variety of microbial proteins in the traditional fermented da-jiang from different regions were different. The production site influences the fermentation in da-jiang. Then we analyzed the functions of the microbial proteins identified in da-jiang, and found that they were mainly involved in the process of protein synthesis, glycometabolism and nucleic acid synthesis. In addtion, we compared the proteins composition in different da-jiang. There are 51 common proteins of naturally fermented da-jiang, and 25 common microbial sources. The main commonly microbial sources of fungal proteins are Saccharomyces cerevisiae and Schizosaccharomyces; the main commonly microbial sources of bacterial proteins are Enterococcus faecalis, Leuconostoc mesenteroides, Acinetobacter baumannii, and Bacillus subtilis. These common microbes play the predominant role in da-jiang fermentation. The present results help us to understand the fermentation of da-jiang and improve the quality and safety of final products in the future.

PRACTICAL APPLICATION

The study illustrated metaproteome of microbiota in traditional fermented soybean paste, da-jiang, by sodium dodecyl sulfonate-polyacrylamide gel electrophoresis (SDS-PAGE) and liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). A method of extracting metaproteome from microbiota in da-jiang was attempted. The findings help to understand the fermentation of da-jiang and improve the quality and safety of da-jiang in fermented industry.