Microbial β-oxidation of synthetic long-chain fatty acids to improve lipid biomethanation

Enhancing beef tallow flavor through enzymatic hydrolysis: Unveiling key aroma precursors and volatile compounds using machine learning

Lipids are critical precursors of aroma compounds in beef tallow. This study investigated how enzymatic hydrolysis treatment affected the aroma precursors and flavor of beef tallow during the manufacturing process. Using gas chromatography-mass spectrometry and high-resolution gas chromatography-ion mobility spectrometry, 100, 111, and 122 aroma compounds were identified in beef tallow at three processing stages namely, raw beef fat, enzymatic hydrolysates, and enzymatic beef tallow. Employing machine learning methods, including fold change analysis, partial least squares-discriminant analysis, and random forest algorithms, we identified 26 potential aroma biomarkers strongly associated with the manufacturing process. Furthermore, debiased sparse partial correlation analysis revealed the significant contribution of C22:2, C22:6 n3, C20:3 n3, C20:1, C18:1 n9t, C18:1 n6t, and C18:2 n6t to aroma compound formation, thereby enhancing our fundamental understanding of flavor precursors and their enzymatic transformation.

Global levels and variations of breast milk fatty acids and triacylglycerols: A systematic review and meta-analysis

Understanding global temporal and spatial variations in breast milk composition is crucial for developing personalized infant nutrition strategies. This study analyzed 46,673 breast milk samples from 171 studies using a random-effects model to evaluate total fatty acids (TFA), sn-2 fatty acids (sn-2 FA), and triacylglycerols (TAG) across lactation stages, regions, and sample years. Results showed that saturated fatty acids (SFA) increased while unsaturated fatty acids (UFA) decreased with prolonged lactation, with corresponding changes in triacylglycerol profiles. Geographically, Africa had the highest SFA and lowest UFA, Asia had the highest PUFA, and Europe had the highest MUFA. Over time, SFA and SFA-dominant TAGs declined, while UFA and UFA-dominant TAGs rose. These variations reflect shifts in maternal diet, infant nutritional needs, and potential growth outcomes, highlighting the importance of monitoring breast milk lipids to optimize infant nutrition strategies.

Decomposing the molecular complexity and transformation of dissolved organic matter for innovative anaerobic bioprocessing

The sustainable transformation and management of dissolved organic matter (DOM) are crucial for advancing organic waste treatment towards resource-oriented processes. However, the intricate molecular complexity of DOM poses significant challenges, impeding a comprehensive understanding of the underlying biochemical processes. Here, we focus on the chemical "dark matter" mining using ultra-high resolution mass spectrometry technologies to elucidate the molecular diversity and transformation in anaerobic bioprocessing of food waste. We developed an analytical framework that reveals the persistence of DOM in the final effluent is mainly determined by its molecular properties, such as carbon chain length, aromaticity, unsaturation, and redox states. Our in-depth characterization and quantitative analysis of key biochemical reactions unveils the evolution of DOM composition, providing valuable insights into the targeted conversion of persistent molecules toward full utilization. Additionally, we establish a correlation between the redox state and energy density of a broad range of DOM molecules, enabling us to comprehend and evaluate their biodegradability. These insights enhance the mechanistic understanding of DOM transformation, guiding the rational design and regulation of sustainable organic waste treatment strategies.

Assembly of Low-Dose Nonionic Surfactant Hydrophobic Functional Groups with Extracellular Polymeric Substances to Destabilize Waste-Activated Sludge and Improve Biomass Energy Recovery

To destabilize the microstructure resulting from microorganism physiology and substance combination in waste-activated sludge (WAS), this study proposes a novel approach by employing nonionic surfactants for pretreatment with a specific focus on alkyl polyglucosides (APG). Inspired by the enhanced dispersibility and targeted hydrophobic interactions of surfactants at low doses, this approach strategically applies APG pretreatment at 0.05 and 0.10 g/g TS, which boosted biogas production by 49.7 and 62.9%, respectively, compared to the control group. The analysis showed that the assembly of APG hydrophobic functional groups with hydrophobic functional groups in EPS enhanced the surface free energy of sludge particles and led to the evacuation of TB-EPS. Microbial diversity analysis reveals shifts in bacteria and archaea in response to APG pretreatment, significant as bacteria Azonexus, Syntrophomonas, Lutispora, and archaea Methanosarcina emerge as new dominant genera. When adding a low dose of APG (<0.10 g/g TS), the destabilization of sludge microstructure (weakening nonfunctional binding between sludge particles and biological enzymes) led to a significant increase in the freedom and activity of enzymes involved in methane metabolism pathways. This study can provide valuable insights for surface interface regulation and efficient biomass energy recovery of complex organic waste.

Organic molecular network analysis reveals transformation signatures of dissolved organic matter during anaerobic digestion process

Identifying the transformation types, i.e., syntheses or decompositions, of organic molecules in complex environmental systems remains a significant challenge. To address this, we propose a new analytical framework, Transformation-based Organic Molecular Ecological Network Analysis (TOMENA) for the systematic recognition and analysis of molecular transformations according to the measurement of high-resolution mass spectrometry (FT-ICR MS) through time-series data. Applying the TOMENA framework, we systematically investigated transformation signatures of dissolved organic matter (DOM) during anaerobic digestion processes. We found a close relationship between molecular transformation and molecular weight in the biodegradation system. A total of 129 transformations were identified, involving carbon numbers ranging from 0 to 24, with 59 of these transformations concentrated in small molecular weight changes involving 1-3 carbons. As the molecular weight corresponding to transformations increased, the proportion of bio-transformations used for decomposition decreased linearly. Simultaneously, large molecules were decomposed and small molecules synthesized, indicating a system tendency to transform molecules towards a medium mass range. Topological analysis of the transformation network further expanded our understanding. We discovered that molecular transformations did not follow the shortest path, as the path distance was significantly longer than in random networks (2.558 vs. 2.383). We identified that N-containing transformations were centrally located in the system through edge analysis. However, the transformations' position did not coincide with functional importance. A comprehensive indicator of irreplaceability and usage frequency revealed that C(+1)H(+3)O(+2)N(-1), C(+1)H(+2), O(+1), C(+3)H(+4)O(+2), and H(-2)O(+1) are critical transformation pathways in the system, showing the top 5 efficiency contributions. Our developed TOMENA workflow provides novel insights and robust methodological support for future research, advancing our understanding of molecular transformations in complex biodegradation system.

Biological/physical particles interact to degrade marine oil spills

After marine oil spills, suspended physical particles and extracellular polymeric substances (EPS) secreted by bacteria can aggregate with oil to form marine oil snow (MOS), which determines the vertical migration and biodegradation processes of the submerged oil. Here, we investigated the biodegradation of oil spills during the formation of MOS under different average energy dissipation rates (ε) and different ratios of particles. Furthermore, we elucidated the biodegradation mechanism of oil spills from a spatiotemporal perspective. The ε plays a major role (either promoting or inhibiting) in the biodegradation effect of oil spills, and there is a proportional threshold for biological/physical particles, which can regulate the ε's effect on degradation. The oil-water interfacial tension, the encapsulation of oil droplets by particles, hydrogen bonds, and the vertical distribution of oil droplets (suspended or deposited) will also jointly affect the particles threshold on this basis, thereby influencing the biodegradation of oil spills. When the proportion of XG exceeds the threshold (kaolinite: XG = 1:3 at 150 rpm and 1:1 at 200 rpm), the originally promotive role of ε on n-alkane degradation shifts to inhibition, while its inhibition impact on PAHs biodegradation shifts to enhancement, respectively. Notably, in nearshore and extreme environments (storm or strong wave conditions), particles are more conducive to the degradation of n-alkanes and PAHs, respectively. This study will further broaden the research perspective on the environmental behavior of marine oil spills in the presence of MOS and providing a theoretical basis for predicting the fate of oil spills in nearshore environments.

Mixtures of Algal Oil and Terrestrial Oils in Diets of Tiger Puffer (Takifugu rubripes)

The n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) have a key role in maintaining fish growth and health. However, fish oil (FO), the main source of n-3 LC-PUFAs, is in relative shortage due to the rapid development of the aquaculture industry. In this study, we investigated the efficacy of replacing fish oil with mixtures of algal oil (AO) from Schizochytrium sp. and terrestrially sourced oils (animal oil poultry oil (PO) or vegetable oil rapeseed oil (RO)) in the diets of juvenile tiger puffer (average initial body weight 23.8 ± 1.51 g). An 8-week feeding trial was conducted using three experimental diets: a control diet containing 6% added FO (control FO-C) and two diets with 3% AO + 3% PO or RO (groups AO+PO and AO+RO, respectively), replacing FO. Each diet was fed to triplicate tanks with 25 fish in each tank. The weight gain, feed conversion ratio, body composition, and serum biochemical parameters were not significantly different among the three groups, except that the AO+PO group had a significantly lower muscle lipid content than the other two groups. The AO-added diets significantly increased the DHA content in whole fish, muscle, and liver samples but significantly reduced the EPA content. The oil mixture treatments significantly increased the contents of monounsaturated fatty acid (MUFA) but significantly decreased the contents of saturated fatty acids (SFAs) in the liver and whole fish samples. However, the MUFA and SFA contents in the muscle samples were not significantly different among the dietary groups. The diets with oil mixtures did not affect the hepatic histology but tended to result in the atrophy of intestinal villi. The treatment diets downregulated the hepatic gene expression of proinflammatory cytokines (il-1β and tnf-α) and the fibrosis marker gene, acta2. However, the AO+PO diet inhibited the intestinal gene expression of the tight junction protein, claudin 18. In the muscle, the treatment diets upregulated the expression of genes related to cell differentiation and apoptosis (myod, myog, myf6, myf5, bcl-2, and bax). In conclusion, Schizochytrium sp. oil in combination with terrestrial oils (poultry oil or rapeseed oil) can be an effective alternative to fish oil in the diets of tiger puffer, but the mixing strategy may be better modified in consideration of intestinal health.

Understanding the microbial processes on carbon brushes that accelerate methanogenesis of long-chain fatty acids in anaerobic digestion

Lipids offer high energy recovery potential during anaerobic digestion (AD), but their hydrolysis generates long-chain fatty acids (LCFAs), which are difficult to biodegrade. The introduction of microbial electrolysis cells has been widely recognized as a promising strategy to enhance AD. However, it is still under debate whether the electrical circuit needs to be connected, as certain electrodes with large specific surface areas have been reported to enhance direct interspecies electron transfer (DIET) without requiring an external power supply. Here we confirmed that the carbon brush anode pre-acclimated with electroactive bacteria (EAB) was able to accelerate LCFA methanation. Although the applied potential achieved a rapid methane production, the coupling of homoacetogenesis and electrogenesis consumed part of the bioelectrohydrogen, reducing the maximum methane production rate by 5-13 %. In the AD system with only carbon brushes added, the dominant methanogens shifted from Methanosarcina in solution to Methanothrix on brushes. Pre-enriching EAB further established a composite mechanism, with DIET driven by Syntrophomonas, Geobacter and Methanothrix as the primary pathway, and interspecies hydrogen transfer mediated by Methanospirillum as a complementary process, collectively optimizing LCFA methanation. Genetic regulation underlying microbial tolerance to high LCFA concentrations was then elucidated, underscoring the critical role of combining immobilized electrodes and pre-acclimated EAB in adapting to LCFA stress and improving lipid-rich wastewater treatment.

Effects of micro-magnetite on anaerobic co-digestion of waste activated sludge and slaughterhouse waste: Microbial community and metabolism analyses

Micro-magnetite has been widely applied to improve anaerobic digestion (AD) performance, while comprehensive investigation of microbial community succession, metabolic pathway and magnetite fate remains unclear. In the current study, the effects of micro-magnetite (Fe3O4) on anaerobic co-digestion (AcD) of waste activated sludge and slaughterhouse waste were investigated. Experimental results indicated that the cumulative methane production was significantly increased from 484.6 mL/g VS to 524.4 mL/g VS with 0.8 g/L Fe3O4 addition. Recycled magnetite remained the initial physicochemical properties, including morphology, particle size and crystal structure, as evidenced by various characterization methods. Microbial community analysis indicated that magnetite addition enriched syntrophic bacteria (Armatimonadota, Syntrophomonas and Petrimonas) and methanogens (Methanosarcina). Metagenomic sequencing analysis demonstrated that hydrolysis and acidogenesis metabolic pathways were reinforced by magnetite addition. Meanwhile, the magnetite stimulated the direct interspecies electron transfer via enriching syntrophic microbes (Syntrophomonas and Methanosarcina) and conductive pili functional genes (pilA, mshA and mshC), finally achieving higher cumulative methane yield. This study provided in-depth investigation of the methane production facilitated by micro-magnetite addition and the magnetite fate during the AcD process.

Micro-nano bubble ozonation for effective treatment of ibuprofen-laden wastewater and enhanced anaerobic digestion performance

The pharmaceutical industry plays a crucial role in driving global economic growth but also poses substantial environmental challenges, particularly in the efficient treatment of production wastewater. This study investigates the efficacy of micro-nano bubble (MNB) ozonation for treating high-strength ibuprofen (IBU)-laden wastewater (49.9 ± 2.3 mg/L) and mitigating its inhibitory effects on the anaerobic digestion (AD) of intralipid (IL)-laden wastewater. Our findings demonstrated that MNB ozonation achieved a 99.0 % removal efficiency of IBU within 70 min, significantly surpassing the 69.8 % efficiency observed with conventional ozonation under optimal conditions. Both conventional and MNB ozonation primarily transformed IBU through oxidation processes, including hydroxylation and the conversion of CH bonds to C = O groups, along with carbon cleavage. However, MNB ozonation markedly reduced the toxicity of IBU-laden wastewater by further transforming toxic by-products, particularly under mildly alkaline conditions (pH 7.2 and 9.0). This reduction in toxicity led to a significant improvement in subsequent AD performance; specifically, a 70-min MNB ozonation pretreatment enhanced methane production by 48.1 %, increased chemical oxygen demand removal by 35.6 %, and reduced fatty acid accumulation compared to the control without pretreatment. Additionally, the effluent from MNB ozonation positively impacted the microbial community, particularly by enriching syntrophic bacteria and methanogens. Overall, these findings offered new insights into the behavior and toxicity of IBU oxidation by-products in both conventional and MNB ozonation processes. Furthermore, this study proposed a novel strategy for the combined treatment of IBU- and IL-laden wastewaters, establishing a robust foundation for advancing MNB ozonation technology in engineered pharmaceutical wastewater treatment.

Cascading Pathways Regulate the Biotransformations of Eight Fluorotelomer Acids Performed by Wastewater Microbial Communities

Polyfluoroalkyl substances can be biotransformed in natural or engineered environmental systems to generate perfluoroalkyl acids (PFAAs). Data are needed to support the development of biotransformation pathway prediction tools that simulate biotransformation pathways of polyfluoroalkyl substances in specific environmental systems. The goal of this study was to experimentally evaluate the biotransformation of eight structurally similar fluorotelomer acids to identify biotransformation products and propose biotransformation pathways. We selected six fluorotelomer carboxylic acids and two fluorotelomer sulfonic acids and employed a biotransformation test system in which batch reactors are seeded with aerobic wastewater microbial communities. We identified 111 biotransformation products among the eight parent compounds, 58 of which represent unique chemical structures. Many of the biotransformation products are the result of apparent dehydrogenation, monohydroxylation, alcohol oxidation, decarboxylation, HF-elimination, and reductive defluorination biotransformations. We use these data to propose cascading biotransformation pathways that are regulated by integrated and synergistic α-oxidation-like, β-oxidation-like, and defluorination biotransformations that result in the formation of terminal PFAAs of varying chain length. Our data provide a comprehensive view on the aerobic biotransformation of fluorotelomer acids and our results can be used to support the ongoing development of biotransformation pathway prediction tools.

Biostimulation accelerates landfill stabilization and resource utilization efficiency, providing feasible technical support for the overall lifecycle management of landfills

Although sanitary landfill is one of the principal municipal solid waste (MSW) treatment and disposal methods, its limitations, such as insufficient use of resources, long stability time, and high risk of environmental pollution, must be urgently resolved. The effect of multifunctional microbial community (MMC) inoculation on MSW landfill process was investigated using simulated anaerobic bioreactor landfill (ABL), and composition and microbial community structure of waste, leachate water quality, and gas production were monitored. MMC inoculation significantly accelerated lignocellulose degradation, and the (Hemicellulose content + Cellulose content)/Lignin content ((C + H)/L) of MMC inoculation treatment was 0.89 ± 0.04 on day 44, which was significantly lower than that of the control group (1.14 ± 0.02). At the end of the landfill process, the reductive organic matter, ammonia nitrogen, and volatile fatty acids in the leachate of the MMC group decreased to 9400.00 ± 288.68, 332.78 ± 5.77, and 79.33 ± 6.44 mg L-1, respectively, significantly lower than those of the control group (24,167.00 ± 208.17, 551.14 ± 5.60, and 156.33 ± 8.22 mg L-1). Meanwhile, MMC inoculation increased the methane production to 118.12 ± 5.42 L kg-1 of dry matter, significantly higher than the output of the control group (60.60 ± 2.24 L kg-1). MMC inoculation optimized the microbial community structure in ABL and increased lignocellulose-degrading microorganisms (Brevundimonas, Cellvibrio, Leifsonia, and Devosia) and methanogen (Methanosaeta and Methanoculleus) abundance in the middle stage of landfill. Moreover, MMC introduction improved the abundance of carbon metabolism enzymes and increased saprophytic fungal abundance by 30.09% in the middle stage of landfill. Overall, these findings may help in developing an effective method to increase the lifespan of landfills and enhance their post-closure management.

Biokinetic and microbial insights into regulatory mechanisms of long-chain fatty acid degradation during food waste-lipid co-digestion within anaerobic membrane bioreactor

This study investigated the effects of varying lipid ratios on the anaerobic co-digestion of high-lipid food waste (FW) in a mesophilic anaerobic membrane bioreactor (AnMBR). At a lipid concentration of 5 %, optimal biogas production (3.84 L/L/d) and lipid removal efficiency (78 %) were achieved; however, increasing lipid concentrations resulted in significant accumulations of long-chain fatty acids (LCFAs) and volatile fatty acids (VFAs). Batch tests further demonstrated the impact of various types of LCFAs, with stearic acid showing the slowest microbial growth rate (0.033d-1), confirming its role in the accumulation of acetate-dominated VFAs, potentially limiting the methanogenesis process at elevated lipid levels. Furthermore, at 8 % lipid content, the downregulation of key LCFA degradation enzymes and dominance of hydrogenotrophic methanogens indicated adverse conditions. The importance of the intricate interplay between LCFA degradation kinetics and microbial community for the system efficiency was evidenced, offering insights for optimizing and managing high-lipidic wastes.

Impact of impeller design on anaerobic digestion: Assessment of mixing dynamics, methane yield, microbial communities and digestate dewaterability

The efficiency of anaerobic digestion (AD) processes is intricately tied to mixing quality. This research investigates the influence of two impeller types, namely a helical ribbon impeller (HRI) and a pitched-blade impeller (PBI), on key aspects of AD. The investigation encompassed mixing dynamics, methane production, microbial communities, and the previously unexplored impact on digestate dewaterability. Results show that agitation with the PBI exhibited stratification, with bottom layer total solids (TS) values of 3.1% for the PBI and 2.6% for the HRI. Nevertheless, methane yield remained unchanged, averaging 286 LN/kg volatile solids (VS)added. Slower mixing with the HRI achieved more uniform mixing and reduced energy requirements. Additionally, impeller type significantly affected digestate dewaterability, leading to a 3.8% increase in TS of the dewatered sludge when using the PBI. These findings highlight the importance of considering mixing not only for methane production and reduced maintenance but also for achieving optimal digestate dewaterability.

Kinetic study on anaerobic digestion of long-chain fatty acid enhanced by activated carbon adsorption and direct interspecies electron transfer

This study applied granular activated carbon (GAC) to improve the anaerobic digestion of long-chain fatty acid (LCFA). New kinetics were considered to describe the effect of GAC on the LCFA degradation, including i) The adsorption kinetics of GAC for LCFA, ii) The β-oxidation pathway of LCFA, iii) The attached biomass improved by direct interspecies electron transfer (DIET). The developed model simulated the anaerobic digestion of stearic acid, palmitic acid, myristic acid, and lauric acid with 1.00 and 2.00 g l-1 of GAC. The simulation results suggested that adding GAC led to the increase of km,CnGAC and km,acGAC. As the concentration of GAC increased, the values of kinetic parameters increased while the accumulated acetate concentration decreased. Thus, GAC improved the kinetic parameters of the attached syntrophic communities.

Microbial community changes and metabolic pathways analysis during waste activated sludge and meat processing waste anaerobic co-digestion

Waste activated sludge (WAS) and meat processing waste (MPW) were acted as co-substrates in anaerobic co-digestion (AcD), and biochemical methane potential (BMP) test was carried out to investigate the methane production performances. Microbial community structure and metabolic pathways analyses were conducted by 16S rRNA high-throughput sequencing and functional prediction analysis. BMP test results indicated that AcD of 70% WAS+30% MPW and 50% WAS+50% MPW (VS/VS) could significantly improve methane yield to 371.05 mL/g VS and 599.61 mL/g VS, respectively, compared with WAS acting as sole substrate (191.87 mL/g VS). The results of microbial community analysis showed that Syntrophomonas and Petrimonas became the dominant bacteria genera, and Methanomassiliicoccus and Methanobacterium became the dominant archaea genera after MPW addition. 16S functional prediction analysis results indicated that genes expression of key enzymes involved in syntrophic acetate oxidation (SAO), hydrogenotrophic and methylotrophic methanogenesis were up-regulated, and acetoclastic methanogenesis was inhibited after MPW addition. Based on these analyses, it could be inferred that SAO combined with hydrogenotrophic and methylotrophic methanogenesis was the dominant pathway for organics degradation and methane production during AcD. These findings provided systematic insights into the microbial community changes and metabolic pathways during AcD of WAS and MPW.

Insights into the seasonal changes in the taxonomic and functional diversity of bacteria in the eastern Arabian Sea: Shotgun metagenomics approach

The eastern Arabian Sea (EAS) is known for its unique oceanographic features such as the seasonal monsoonal winds, upwelling of nutrient-rich waters and a significant increase in primary productivity during the monsoon season. In this study, we utilised the shotgun metagenomics approach to determine the seasonal variations in bacterial taxonomic and functional profiles during the non-monsoon and monsoon seasons in the EAS. Significant seasonal variations in the bacterial community structure were observed at the phylum and genera levels. These findings also correspond with seasonal shifts in the functional profiles of the bacterial communities based on the variations of genes encoding enzymes associated with different metabolic pathways. Pronounced seasonal variation of bacterial taxa was evident with an increased abundance of Idiomarina, Marinobacter, Psychrobacter and Alteromonas of Proteobacteria, Bacillus and Staphylococcus of Firmicutes during the non-monsoon season. These taxa were linked to elevated nucleotide and amino acid biosynthesis, amino acid and lipid degradation. Conversely, during the monsoon, the taxa composition changed with Alteromonas, Candidatus Pelagibacter of Proteobacteria and Cyanobacteria Synechococcus; contributing largely to the amino acid and lipid biosynthesis, fermentation and inorganic nutrient metabolism which was evident from functional analysis. Regression analysis confirmed that increased seasonal primary productivity significantly influenced the abundance of genes associated with carbohydrate, protein and lipid metabolism. These highlight the pivotal role of seasonal changes in primary productivity in shaping the bacterial communities, their functional profiles and driving the biogeochemical cycling in the EAS.

Low dose phosphorus supplementation is conducive to remediation of heavily petroleum-contaminated soil-From the perspective of hydrocarbon removal and ecotoxicity risk control

Biostimulation by supplementing of nitrogen and phosphorus nutrients is a common strategy for remediation of petroleum-polluted soils. However, the dosage influence of exogenous nitrogen or phosphorus on petroleum hydrocarbon removal and soil ecotoxicity and microbial function remain unclear. In this study, we compared the efficiencies of hydrocarbon degradation and ecotoxicity control by experiment conducted over addition of inorganic nitrogen or phosphorus at C/N ratio of 100/10, C/N/P ratio of 100/10/1, and C/P ratio of 100/1 in a heavily petroleum-contaminated loessal soil with 12,320 mg/kg of total petroleum hydrocarbon (TPH) content. A 90-day incubation study revealed that low-dose of phosphorus addition with the C/P ratio of 100/1 promoted hydrocarbon degradation and reduced soil ecotoxicity. Microbial community composition analysis suggested that phosphorus addition enriched hydrocarbon degrader Gordonia and Mycolicibacterium genus. The key enzymes EC 5.3.3.8, EC 6.2.1.20 and EC 6.4.1.1 which referred to degradation of long-chain hydrocarbons, unsaturated fatty acids and pyruvate metabolism were abundance by phosphorus supplementation. While nitrogen addition at C/N ratio of 100/10 or C/N/P ratio of 100/10/1 inhibited hydrocarbon degradation and exacerbated soil ecotoxicity due to promoting denitrification and coupling reactions with hydrocarbons. Our results suggested that low-dose phosphorus addition served as a favorable strategy to promote crude oil remediation and ecotoxicity risk control in heavily petroleum-contaminated soil. Hence, the application of suitable doses of exogenous biostimulants is an efficient approach to restore the ecological functions of organically contaminated soils.

Integration of genetic engineering and multi-factor fermentation optimization for co-production of carotenoid and DHA in Schizochytrium sp

Schizochytrium sp., a microalga with high lipid content, holds the potential for co-producing docosahexaenoic acid (DHA) and carotenoids. In this study, the ability of Schizochytrium sp. to naturally produce carotenoids was systematically explored. Further, by enhancing the precursor supply of geranylgeranyl diphosphate, regulating carbon source through sugar limitation fermentation and employing a combination of response surface methodology and artificial neural networks to precisely optimize nitrogen sources, a new record of 43-fold increase in β-carotene titer was achieved in the 5L bioreactor (653.2 mg/L). Meanwhile, a high DHA content was maintained (13.4 g/L). Furthermore, the use of corn stover hydrolysate has effectively lowered the production costs of carotenoid and DHA while sustaining elevated production levels (with total carotenoid titer and DHA titer reached 502.0 mg/L and 13.2 g/L, respectively). This study offers an efficient and cost-effective method for the co-production of carotenoid and DHA in Schizochytrium sp..

Distinctive species interaction patterns under high nitrite stress shape inefficient denitrifying phosphorus removal performance

Denitrifying phosphorus removal using nitrite as an electron acceptor is an innovative, resource-efficient approach for nitrogen and phosphorus removal. However, the inhibitory effects of nitrite on anoxic phosphorus uptake and process stability are unclear. This study investigated the total phosphorus removal performance under nitrite stress and analyzed microbiome responses in 186 sludge samples. The results indicated that the total phosphorus removal rates and dominant taxon abundance were highly similar under nitrite stress. High nitrite stress induced a community-state shift, leading to unstable dynamics and decreased total phosphorus removal. This shift resulted from increased species cooperation. Notably, the shared genera OLB8 and Zoogloea under non-inhibitory nitrite stress, suggesting their vital roles in mitigating nitrite stress by enhancing carbon and energy metabolism. The response patterns of these bacterial communities to high nitrite stress can guide the design and optimization of high-nitrogen wastewater reactors.

Effect of operational parameters on the performance of an anaerobic sequencing batch reactor (AnSBR) treating protein-rich wastewater

Treating protein-rich wastewater using cost-effective and simple-structured single-stage reactors presents several challenges. In this study, we applied an anaerobic sequencing batch reactor (AnSBR) to treat protein-rich wastewater from a slaughterhouse. We focused on identifying the key factors influencing the removal of chemical oxygen demand (COD) and the settling performance of the sludge. The AnSBR achieved a maximum total COD removal of 90%, a protein degradation efficiency exceeding 80%, and a COD to methane conversion efficiency of over 70% at organic loading rates of up to 6.2 g COD L-1 d-1. We found that the variations in both the organic loading rate within the reactor and the hydraulic retention time in the buffer tank had a significant effect on COD removal. The hydraulic retention time in the buffer tank and the reactor, which determined the ammonification efficiencies and the residual carbohydrate concentrations in the reactor liquid, affected the sludge settleability. Furthermore, the genus Clostridium sensu stricto 1, known as protein- and lipids-degraders, was predominant in the reactor. Statistical analysis showed a significant correlation between the core microbiome and ammonification efficiency, highlighting the importance of protein degradation as the governing process in the treatment. Our results will provide valuable insights to optimise the design and operation of AnSBR for efficient treatment of protein-rich wastewater.

Comprehensive study of the combined effects of biochar and iron-based conductive materials on alleviating long chain fatty acids inhibition in anaerobic digestion

This study investigated the feasibility of alleviating the negative influence of long-chain fatty acids (LCFAs) on anaerobic digestion by biochar, micron zero-valent iron, micron-magnetite (mFe3O4) and their combination. The results demonstrate that co-addition of biochar and 6 g/L mFe3O4 (BC+6 g/L mFe3O4) increased cumulative methane production by 50% as suffered from LCFAs inhibition exerted by 2 g/L glycerol trioleate. The BC+6 g/L mFe3O4 did best in accelerating total organic carbon degradation and volatile fatty acids conversion, through successively enriching Bacteroides, Corynebacterium, and DMER64 to dominant the bacterial community. The proportion of acetotrophic Methanothrix that could alternatively reduce CO2 to methane by accepting electrons via direct interspecies electron transfer (DIET) was 0.09% with BC+6 g/L mFe3O4, nine times more than the proportion in control. Prediction of functional genes revealed the enrichment of the bacterial secretion system, indicating that BC+6 g/L mFe3O4 promoted DIET by stimulating the secretion of extracellular polymeric substances. This study provided novel insights into combining biochar and iron-based conductive materials to enhance AD performance under LCFAs inhibition.

Effects of microbes in pig farms on occupational exposed persons and the environment

In terms of pig farming, pig gut microbes have a significant effect on farmers and the farm environment. However, it is still unclear which microbial composition is more likely to contribute to this effect. This study collected a total of 136 samples, including pigs' faeces samples, farmers' faeces samples, samples from individuals who had no contact with any type of farm animal (referred to as 'non-exposed' persons), and environmental dust samples (collected from inside and outside pig houses and the farm) from two pig farms, pig farm A and pig farm B. Whereafter, 16S rRNA sequencing and taxonomic composition analysis were performed. According to the study, compared to non-exposed persons, pig farmers had a significantly higher abundance of 7 genera. In addition, the farmers were grouped according to the duration of their occupational exposure, and it was shown that 4 genera, including Turicibacter, Terrisporobacter, and Clostridium_sensu_stricto_1, exhibited a rise in more frequent contact with pigs. As compared to outside the pig house, the environmental dust has a greater concentration of the 3 bacteria mentioned before. Therefore, these 3 microbes can be considered as co-occurring microbes that may exist both in humans and the environment. Also, the 3 co-occurring microbes are involved in the fermentation and production of short-chain fatty acids and their effectiveness decreased as distance from the farm increased. This study shows that the 3 microbes where pig farmers co-occur with the environment come from pig farms, which provides fresh ideas for preventing the spread of microbial aerosols in pig farms and reducing pollution.

Multi-omics analysis unravels effects of salt and oil on substance transformation, microbial community, and transcriptional activity in food waste anaerobic digestion

In this study, through quantitative detection of key substances and enzyme activities, an integrated analysis of 16S rRNA sequencing and metatranscriptomics revealed the mechanisms by which salt and oil influence the biotransformation process during anaerobic digestion (AD). The results demonstrated that a salt concentration of 6 g/L promoted lipid metabolism and hydrogenotrophic methanogenesis, while inhibiting the acetoclastic pathway. An oil concentration of 5 g/L facilitated the expression of key enzyme-encoding genes involved in β-oxidation of long-chain fatty acids, transcription, and acetoclastic methanogenesis. It also promoted the enrichment of syntrophic propionate/butyrate oxidation bacteria (Syntrophomonas and DMER64). Salt/oil co-addition enhanced the expression of genes related to glucose metabolism, amino acid metabolism, organic acid synthesis, and quorum sensing. Furthermore, salt/oil co-addition inhibited the secretion of key enzymes related to methanogens by impeding the transcription process. Collectively, these findings provide systematic insights into how salt and oil affect the biochemical metabolic mechanisms of AD.

Metabolic responses and microbial community changes to long chain fatty acids: Ammonia synergetic co-inhibition effect during biomethanation

Anaerobic co-digestion is an established strategy for increasing methane production of substrates. However, substrates rich in proteins and lipids could cause a long chain fatty acids (LCFA)-ammonia synergetic co-inhibition effect. The microbial mechanisms of this co-inhibition are still unclear. The current study explored the effect of the synergetic co-inhibition on microbial community changes and prediction of metabolic enzymes to reveal the microbial mechanisms of the co-inhibition effect. The results indicated that during the synergetic co-inhibition, methanogens were mainly affected by ammonia. Decreased relative abundances of Petrimonas (82%) and Paraclostridium (67%) showed that ammonia inhibition contributed to the suppression of LCFA β-oxidation under the synergetic co-inhibition conditions. The accumulation of more LCFA could further suppress microorganisms' activities involved in several steps of anaerobic digestion. Finally, decrease of critical enzymes' abundances confirmed the synergetic co-inhibition effect. Overall, the current study provides novel insights for the alleviation of synergetic co-inhibition during anaerobic digestion.

Presence and role of viruses in anaerobic digestion of food waste under environmental variability

BACKGROUND

The interaction among microorganisms in the anaerobic digestion of food waste (ADFW) reactors lead to the degradation of organics and the recycling of energy. Viruses are an important component of the microorganisms involved in ADFW, but are rarely investigated. Furthermore, little is known about how viruses affect methanogenesis.

RESULTS

Thousands of viral sequences were recovered from five full-scale ADFW reactors. Gene-sharing networks indicated that the ADFW samples contained substantial numbers of unexplored anaerobic-specific viruses. Moreover, the viral communities in five full-scale reactors exhibited both commonalities and heterogeneities. The lab-scale dynamic analysis of typical ADFW scenarios suggested that the viruses had similar kinetic characteristics to their prokaryotic hosts. By associating with putative hosts, a majority of the bacteria and archaea phyla were found to be infected by viruses. Viruses may influence prokaryotic ecological niches, and thus methanogenesis, by infecting key functional microorganisms, such as sulfate-reducing bacteria (SRB), syntrophic acetate-oxidizing bacteria (SAOB), and methanogens. Metabolic predictions for the viruses suggested that they may collaborate with hosts at key steps of sulfur and long-chain fatty acid (LCFA) metabolism and could be involved in typical methanogenesis pathways to participate in methane production.

CONCLUSIONS

Our results expanded the diversity of viruses in ADFW systems and suggested two ways that viral manipulated ADFW biochemical processes. Video Abstract.

Biodegradation of MC-LR and its key bioactive moiety Adda by Sphingopyxis sp. YF1: Comprehensive elucidation of the mechanisms and pathways

Microcystins (MCs) are harmful to the ecology and public health. Some bacteria can degrade MCs into Adda, but few can destroy Adda. Adda is the key bioactive moiety of MCs and mainly contributes to hepatotoxicity. We had previously isolated an indigenous novel bacterial strain named Sphingopyxis sp. YF1 that can efficiently degrade MCs and its key bioactive moiety Adda, but the mechanisms remained unknown. Here, the biodegradation mechanisms and pathways of Adda were systematically investigated using multi-omics analysis, mass spectrometry and heterologous expression. The transcriptomic and metabolomic profiles of strain YF1 during Adda degradation were revealed for the first time. Multi-omics analyses suggested that the fatty acid degradation pathway was enriched. Specifically, the expression of genes encoding aminotransferase, beta oxidation (β-oxidation) enzymes and phenylacetic acid (PAA) degradation enzymes were significantly up-regulated during Adda degradation. These enzymes were further proven to play important roles in the biodegradation of Adda. Simultaneously, some novel potential degradation products of Adda were identified successfully, including 7‑methoxy-4,6-dimethyl-8-phenyloca-2,4-dienoic acid (C₁₇H₂₂O₃), 2-methyl-3‑methoxy-4-phenylbutyric acid (C₁₂H₁₆O₃) and phenylacetic acid (PAA, C₈H₈O₂). In summary, the Adda was converted into PAA through aminotransferase and β-oxidation enzymes, then the PAA was further degraded by PAA degradation enzymes, and finally to CO₂ via the tricarboxylic acid cycle. This study comprehensively elucidated the novel MC-LR biodegradation mechanisms, especially the new enzymatic pathway of Adda degradation. These findings provide a new perspective on the applications of microbes in the MCs polluted environment.

Biochar addition augmented the microbial community and aided the digestion of high-loading slaughterhouse waste: Active enzymes of bacteria and archaea

The biogas production (BP), volatile fatty acids (VFAs), microbial communities, and microbes' active enzymes were studied upon the addition of biochar (0-1.5%) at 6% and 8% slaughterhouse waste (SHW) loadings. The 0.5% biochar enhanced BP by 1.5- and 1.6-folds in 6% and 8% SHW-loaded reactors, respectively. Increasing the biochar up to 1.5% caused a reduction in BP at 6% SHW. However, the BP from 8% of SHW was enhanced by 1.4-folds at 1.5% biochar. The VFAs production in all 0.5% biochar amended reactors was highly significant compared to control (p-value < 0.05). The biochar addition increased the bacterial and archaeal diversity at both 6% and 8% SHW loadings. The highest number of OTUs at 0.5% biochar were 567 and 525 in 6% and 8% SHW, respectively. Biochar prompted the Clostridium abundance and increased the lyases and transaminases involved in the degradation of lipids and protein, respectively. Biochar addition improved the Methanosaeta and Methanosphaera abundance in which the major enzymes were reductase and hydrogenase. The archaeal enzymes showed mixed acetoclastic and hydrogenotrophic methanogenesis.