Metagenomic analysis and characterization of acidogenic microbiome and effect of pH on organic acid production

Cellulose Degradation Enzymes in Filamentous Fungi, A Bioprocessing Approach Towards Biorefinery

The economic exploration of renewable energy resources has hot fundamentals among the countries besides dwindling energy resources and increasing public pressure. Cellulose accumulation is a major bio-natural resource from agricultural waste. Cellulases are the most potential enzymes that systematically degrade cellulosic biomass into monomers which could be further processed into several efficient value-added products via chemical and biological reactions including useful biomaterial for human benefits. This could lower the environmental risks problems followed by an energy crisis. Cellulases are mainly synthesized by special fungal genotypes. The strain Trichoderma orientalis could highly express cellulases and was regarded as an ideal strain for further research, as the genetic tools have found compatibility for cellulose breakdown by producing effective cellulose-degrading enzymes. This strain has found a cellulase production of about 35 g/L that needs further studies for advancement. The enzyme activity of strain Trichoderma orientalis needed to be further improved from a molecular level which is one of the important methods. Considering synthetic biological approaches to unveil the genetic tools will boost the knowledge about commercial cellulases bioproduction. Several genetic transformation methods were significantly cited in this study. The transformation approaches that are currently researchers are exploring is transcription regulatory factors that are deeply explained in this study, that are considered essential regulators of gene expression.

Advances in sewage sludge application and treatment: Process integration of plasma pyrolysis and anaerobic digestion with the resource recovery

Sewage sludge (SS) is an environmental issue due to its high organic content and ability to release hazardous substances. Most of the treatments available are biological, thermal hydrolysis, mechanical (ultrasound, high pressure, and lysis), chemical with oxidation (mainly ozonation), and alkali pre-treatments. Other treatment methods include landfill, wet oxidation, composting, drying, stabilization, incineration, pyrolysis, carbonization, liquefaction, gasification, and torrefaction. Some of these SS disposal methods damage the ecosystem and underutilize the potential resource value of SS. These challenges must be overcome with an innovative technique for the improvement of SS's nutritional value, energy content, and usability. This review proposes plasma pyrolysis and anaerobic digestion (AD) as promising SS treatment technologies. Plasma pyrolysis pre-treats SS to make it digestible by AD bacteria and immobilizes the heavy metals. The addition of Char to the upstream AD process increases the quantity and quality of biogas produced while enhancing the nutrients in the digestate. These two processes are integrated at high temperatures, thus creating concerns about their energy demand. These challenges are offset by the generated energy that can run the treatment plant or be sold to the grid, generating additional cash. Plasma pyrolysis wastes can also be converted into biochar, organic fertilizer, or soil conditioner. These combined technologies' financial sustainability depends on the treatment facility's circumstances and location. Plasma pyrolysis and AD can treat SS sustainably and provide nutrients and resources. This paper explains the co-process treatment route's techno-economic prospects, challenges, and recommendations for the future application of SS valorization and resource recovery.

A comprehensive review on current status and future perspectives of microbial volatile fatty acids production as platform chemicals

Volatile fatty acids (VFA), the secondary metabolite of microbial fermentation, are used in a wide range of industries for production of commercially valuable chemicals. In this review, the fermentative production of VFAs by both pure as well mixed microbial cultures is highlighted along with the strategies for enhancing the VFA production through innovations in existing approaches. Role of conventionally applied tools for the optimization of operational parameters such as pH, temperature, retention time, organic loading rate, and headspace pressure has been discussed. Furthermore, a comparative assessment of above strategies on VFA production has been done with alternate developments such as co-fermentation, substrate pre-treatment, and in situ removal from fermented broth. The review also highlights the applications of different bioreactor geometries in the optimum production of VFAs and how metagenomic tools could provide a detailed insight into the microbial communities and their functional attributes that could be subjected to metabolic engineering for the efficient production of VFAs.

Lactic acid production from mesophilic and thermophilic fermentation of food waste at different pH

It is promising to recover lactic acid (LA) from fermentation of food waste (FW). In this study, pH and temperatures were investigated comprehensively to find their effects on LA fermentation, and microbial analyses were used to take insight to the variation of LA production. The results showed that mesophilic fermentation benefited hydrolysis and acidification, leading to a high yield of LA, while thermophilic conditions restricted other producers at low pH, leading to a high purity of LA. Lactobacillus amylolyticus was the main LA producer under thermophilic conditions, but Thermoanaerobacterium thermosaccharolyticum boomed at pH 5.0-6.0 and it converted LA partly to butyric acid. Simultaneously, Bacillus coagulans also increased and improved the optical purity (OP) of L-LA. From a series of this study, an operational condition of pH 5.5 and temperature of 52 °C would be potentially suitable for lactate fermentation of FW with high purity of 89%, while a stable LA production with an OP of 68% was achieved at 55 °C and pH 6.0.

Perspectives of nervonic acid production by Yarrowia lipolytica

Nervonic acid (cis-15-tetracosenoic acid, 24:1Δ15) is a long chain monounsaturated fatty acid, mainly exists in white matt er of the human brains. It plays an important role in the development of nervous system and curing neurological diseases. The limited natural sources and high price are considered limiting factors for the extensive application of nervonic acid. Yarrowia lipolytica is a high lipid producing yeast and engineered strain which can produce nervonic acid. The biosynthesis of nervonic acid has yet to be investigated, although the metabolism has been examined for couple of years. Normally, oleic acid is considered the origin of nervonic acid synthesis through fatty acid prolongation, where malonyl-CoA and acyl-CoA are initially concise by 3-ketoacyl-CoA synthase (KCS). To meet the high requirement of industrial production, the optimization of fermentation and bioreactors configurations are necessary tools to be carried out. This review article summarizes the research literature on advancements and recent trends about the production, synthesis and properties of nervonic acid.

Current understanding and perspectives in anaerobic digestion based on genome-resolved metagenomic approaches

Anaerobic digestion (AD) is a technique that can be used to treat high concentrations of various organic wastes using a consortium of functionally diverse microorganisms under anaerobic conditions. Methane gas, a beneficial by-product of the AD process, is a renewable energy source that can replace fossil fuels following purification. However, detailed functional roles and metabolic interactions between microbial populations involved in organic waste removal and methanogenesis are yet to be known. Recent metagenomic approaches based on advanced high-throughput sequencing techniques have enabled the exploration of holistic microbial taxonomy and functionality of complex microbial populations involved in the AD process. Gene-centric and genome-centric analyses based on metagenome-assembled genomes are a platform that can be used to study the composition of microbial communities and their roles during AD. This review looks at how these up-to-date metagenomic analyses can be applied to promote our understanding and improved the development of the AD process.

The Impact of Host Genotype, Intestinal Sites and Probiotics Supplementation on the Gut Microbiota Composition and Diversity in Sheep

Three sampling strategies with a 16s rRNA high-throughput sequencing and gene expression assay (by RT-PCR) were designed, to better understand the host and probiotics effect on gut microbiota in sheep. Sampling: (1) colon contents and back-fat tissues from small-tailed Han sheep (SHS), big-tailed Hulun Buir sheep (BHBS), and short-tailed Steppe sheep (SHBS) (n = 12, 14, 12); (2) jejunum, cecum and colon contents, and feces from Tan sheep (TS, n = 6); (3) feces from TS at 4 time points (nonfeeding, 30 and 60 feeding days, and stop feeding 30 days) with probiotics supplementation (n = 7). The results indicated SHS had the highest Firmicutes abundance, the thinnest back-fat, and the lowest expression of C/EBPβ, C/EBPδ, ATGL, CFD, and SREBP1. Some bacteria orders and families could be potential biomarkers for sheep breeds with a distinct distribution of bacterial abundance, implying the host genotype is predominant in shaping unique microbiota under a shared environment. The microbiota diversity and Bifidobacterial populations significantly changed after 60 days of feeding but restored to its initial state, with mostly colonies, after 30 days ceased. The microbiota composition was greatly different between the small and large intestines, but somewhat different between the large intestine and feces; feces may be reliable for studying large intestinal microbiota in ruminants.

Metabolism Characteristics of Lactic Acid Bacteria and the Expanding Applications in Food Industry

Lactic acid bacteria are a kind of microorganisms that can ferment carbohydrates to produce lactic acid, and are currently widely used in the fermented food industry. In recent years, with the excellent role of lactic acid bacteria in the food industry and probiotic functions, their microbial metabolic characteristics have also attracted more attention. Lactic acid bacteria can decompose macromolecular substances in food, including degradation of indigestible polysaccharides and transformation of undesirable flavor substances. Meanwhile, they can also produce a variety of products including short-chain fatty acids, amines, bacteriocins, vitamins and exopolysaccharides during metabolism. Based on the above-mentioned metabolic characteristics, lactic acid bacteria have shown a variety of expanded applications in the food industry. On the one hand, they are used to improve the flavor of fermented foods, increase the nutrition of foods, reduce harmful substances, increase shelf life, and so on. On the other hand, they can be used as probiotics to promote health in the body. This article reviews and prospects the important metabolites in the expanded application of lactic acid bacteria from the perspective of bioengineering and biotechnology.

Swine manure valorization in fabrication of nutrition and energy

Renewable energy can boost the growing population's need and rapid budgetary development. To reduce fossil fuel consumption is the initial purpose of renewable and sustainable energy, producing valuable bio-based products. The fermenters, using for pretreatment of swine manure, and involvement of swine carcasses are reported to enhance organic loading rate followed by improved biogas yield on household digesters. The compositions such as animal residues, pathogenic microbes, pharmaceutical residues and nutrient compositions including undigested feed are still confused. Therefore, it is mandatory to optimize and stabilize anaerobic practice and digestate filtration purification for consequential fertilizer consumption. The effective bio-methane recovery from energy-rich compounds is challenging due to slow degradation procedures. The pretreatment procedure could enhance lipid depolymerization and improve anaerobic fermentation. This article deeply focuses on biodegradation of swine manure. The components of this manure were evaluated and established several approaches to improve biogas production. Furthermore, recycling of co-digestates was discussed in detail as fertilizer consumption including hygienic aspects of manure and pretreatment strategies of biomass residues. KEY POINTS: • Co-digestion of manure and carcasses enhance bio-methane production. • Removel of ammonia from biogas digester may improve bio-methane gas. • A strong antimicrobial influence has been reported on biogas production.

Combinations of alkaline hydrogen peroxide and lithium chloride/N,N-dimethylacetamide pretreatments of corn stalk for improved biomethanation

The purpose of this study was to improve methane generation from corn stalk (CS) through alkaline hydrogen peroxide and lithium chloride/N,N-dimethylacetamide (AHP-LiCl/DMAc) pretreatment. Changes in the structures of treated and untreated CSs were investigated, and biomass components, including cellulose, hemicellulose and lignin, were analysed. Our findings revealed that AHP-LiCl/DMAc pretreatment improved accumulative methane yield by forceful delignification and effectively destroyed the structure of cellulose. The AHP-LiCl/DMAc-treated group had a maximum methane yield of 318.6 ± 17.85 mL/g volatile solid, which was 40.08% and 10.10% higher than the maximum methane yields of the untreated and AHP-treated group, respectively. This result showed enhanced cellulose dissolution by the ionic solvent of LiCl/DMAc and improved enzymatic saccharification in fermentative bacteria without structural modifications. The AHP-LiCl/DMAc treated group had higher glucose level, acetate followed by biomethanation process. Furthermore, the decrease in crystallinity indexes for AHP-LiCl/DMAc treated group was reported. Overall, this investigation proved a promising pretreatment approach for enhancing the degradation of CS into reducing sugars and improving methane generation.

Opportunities for holistic waste stream valorization from food waste treatment facilities: a review

Difficult-to-biodegrade fractions (DBFs) generated from the biological treatment of food waste (FW) account for approximately 30% of the actual waste. These wastes are difficult to degrade or are considered indigestible residues of the aerobic and anaerobic fermentation treatment of FW treatment facilities. The currently applied disposal routes for DBFs exert environmental pressure and underutilize waste as resources. Therefore, these challenges must be overcome. An innovative strategy for the enhancement of the energy value and beneficial products from FW and the associated DBFs is proposed in this review. We propose conceptual future optimization routes for FW and DBFs via three types of technology integration. Pyrolysis techniques thoroughly treat DBFs to produce various value-added bio-energy products, such as pyrogenic bio-char, syngas, and bio-oil. Anaerobic digestion treats FW while utilizing pyrolysis products for robust performance enhancement and bio-methane upgrade. This holistic route offers conceptual information and proper direction as crucial knowledge for real application to harness the inherent resources of waste streams generated from FW treatment facilities.

H2 Metabolism revealed by metagenomic analysis of subglacial sediment from East Antarctica

Subglacial ecosystems harbor diverse chemoautotrophic microbial communities in areas with limited organic carbon, and lithological H₂ produced during glacial erosion has been considered an important energy source in these ecosystems. To verify the H₂-utilizing potential there and to identify the related energy-converting metabolic mechanisms of these communities, we performed metagenomic analysis on subglacial sediment samples from East Antarctica with and without H₂ supplementation. Genes coding for several [NiFe]-hydrogenases were identified in raw sediment and were enriched after H₂ incubation. All genes in the dissimilatory nitrate reduction and denitrification pathways were detected in the subglacial community, and the genes coding for these pathways became enriched after H₂ was supplied. Similarly, genes transcribing key enzymes in the Calvin cycle were detected in raw sediment and were also enriched. Moreover, key genes involved in H₂ oxidization, nitrate reduction, oxidative phosphorylation, and the Calvin cycle were identified within one metagenome-assembled genome belonging to a Polaromonas sp. As suggested by our results, the microbial community in the subglacial environment we investigated consisted of chemoautotrophic populations supported by H₂ oxidation. These results further confirm the importance of H₂ in the cryosphere.