Microorganism-regulated mechanisms of temperature effects on the performance of anaerobic digestion

Improving methane production and 4-chlorophenol removal in anaerobic digestion of corn straw by adding Phanerochaete chrysosporium and biochar under microaerobic conditions

The stable lignocellulose structure in the straw is the main obstacle for methane production during its anaerobic digestion, and the residual chlorophenols in the straw further increase the difficulty. In this study, the anaerobic digestion of corn straw containing 4-chlorophenol was enhanced by the addition of Phanerochaete chrysosporium and biochar. The results revealed that P. chrysosporium significantly increased the soluble COD concentration and total COD removal efficiency in the anaerobic digestion of corn straw, which initially contained a small amount of residual oxygen (4.1-4.5 mg/L). The accumulative methane production of the P. chrysosporium-coupled biochar (PC-BC) group and the PC group with P. chrysosporium alone were 232.9 ± 3.0 mL and 201.7 ± 5.1 mL, respectively, which were significantly higher than the control group (19.4 ± 1.0 mL) with the sterilized P. chrysosporium. The presence of biochar increased 4-CP removal rate to 93.3 %, which was 15.2 % higher than the control. Additionally, FTIR analysis indicated that the addition of P. chrysosporium and biochar enhanced the decomposition of lignocellulose structure. Moreover, the sludge capacitance and electron transfer capacity were highest in the PC-BC group. Also, microbial community analysis showed that biochar could enrich dechlorinating bacteria (e.g., Sedimentibacter) and electroactive microorganisms, which further enhanced dechlorination and methanogensis.

A cyclic shift-temperature operation method to train microbial communities of mesophilic anaerobic digestion

Temperature is the critical factor affecting the efficiency and cost of anaerobic digestion (AD). The current work develops a shift-temperature AD (STAD) between 35 °C and 55 °C, intending to optimise microbial community and promote substrate conversion. The experimental results showed that severe inhibition of biogas production occurred when the temperature was firstly increased stepwise from 35 °C to 50 °C, whereas no inhibition was observed at the second warming cycle. When the organic load rate was increased to 6.37 g VS/L/d, the biogas yield of the STAD reached about 400 mL/g VS, nearly double that of the constant-temperature AD (CTAD). STAD promoted the proliferation of Methanosarcina (up to 57.32 %), while severely suppressed hydrogenophilic methanogens. However, when the temperature was shifted to 35 °C, most suppressed species recovered quickly and the excess propionic acid was quickly consumed. Metagenomic analysis showed that STAD also promoted gene enrichment related to pathways metabolism, membrane functions, and methyl-based methanogenesis.

Systematic study of microzooplankton in mass culture of the green microalga Scenedesmus acuminatus and quantitative assessment of its impact on biomass productivity throughout a year

The green microalgae Scenedesmus spp. can grow rapidly and produce significant amounts of protein or lipid. However, frequent microzooplankton contamination leading to reduced biomass productivity has hindered the microalgae commercialization. Here, a comprehensive investigation into harmful microzooplankton species in mass cultures of a commercially promising species Scenedesmus acuminatus were conducted throughout the year. Twenty-five microzooplankton species were identified, with the amoeba Vannella sp. and the ciliate Vorticella convallaria being the most harmful to algal cells. The results indicated that it was the harmful grazers, rather than the overall microzooplankton diversity, led to culture deterioration and reduced biomass yield. Increasing the concentration of algal inoculants or reducing culture temperature during hot summer days were found to be effective in mitigating the impact of these harmful grazers. The findings will contribute to the best management protocol for monitoring and controlling the harmful microzooplankton in mass cultures of S. acuminatus.

Study on the estradiol degradation gene expression and resistance mechanism of Rhodococcus R-001 under low-temperature stress

Estradiol (E2), an endocrine disruptor, acts by mimicking or interfering with the normal physiological functions of natural hormones within organisms, leading to issues such as endocrine system disruption. Notably, seasonal fluctuations in environmental temperature may influence the degradation speed of estradiol (E2) in the natural environment, intensifying its potential health and ecological risks. Therefore, this study aims to explore how bacteria can degrade E2 under low-temperature conditions, unveiling their resistance mechanisms, with the goal of developing new strategies to mitigate the threat of E2 to health and ecological safety. In this paper, we found that Rhodococcus equi DSSKP-R-001 (R-001) can efficiently degrade E2 at 30 °C and 10 °C. Six genes in R-001 were shown to be involved in E2 degradation by heterologous expression at 30 °C. Among them, 17β-HSD, KstD2, and KstD3, were also involved in E2 degradation at 10 °C; KstD was not previously known to degrade E2. RNA-seq was used to characterize differentially expressed genes (DEGs) to explore the stress response of R-001 to low-temperature environments to elucidate the strain's adaptation mechanism. At the low temperature, R-001 cells changed from a round spherical shape to a long rod or irregular shape with elevated unsaturated fatty acids and were consistent with the corresponding genetic changes. Many differentially expressed genes linked to the cold stress response were observed. R-001 was found to upregulate genes encoding cold shock proteins, fatty acid metabolism proteins, the ABC transport system, DNA damage repair, energy metabolism and transcriptional regulators. In this study, we demonstrated six E2 degradation genes in R-001 and found for the first time that E2 degradation genes have different expression characteristics at 30 °C and 10 °C. Linking R-001 to cold acclimation provides new insights and a mechanistic basis for the simultaneous degradation of E2 under cold stress in Rhodococcus adaptation.

Functional conservation of microbial communities determines composition predictability in anaerobic digestion

A major challenge in managing and engineering microbial communities is determining whether and how microbial community responses to environmental alterations can be predicted and explained, especially in microorganism-driven systems. We addressed this challenge by monitoring microbial community responses to the periodic addition of the same feedstock throughout anaerobic digestion, a typical microorganism-driven system where microorganisms degrade and transform the feedstock. The immediate and delayed response consortia were assemblages of microorganisms whose abundances significantly increased on the first or third day after feedstock addition. The immediate response consortia were more predictable than the delayed response consortia and showed a reproducible and predictable order-level composition across multiple feedstock additions. These results stood in both present (16 S rRNA gene) and potentially active (16 S rRNA) microbial communities and in different feedstocks with different biodegradability and were validated by simulation modeling. Despite substantial species variability, the immediate response consortia aligned well with the reproducible CH4 production, which was attributed to the conservation of expressed functions by the response consortia throughout anaerobic digestion, based on metatranscriptomic data analyses. The high species variability might be attributed to intraspecific competition and contribute to biodiversity maintenance and functional redundancy. Our results demonstrate reproducible and predictable microbial community responses and their importance in stabilizing system functions.

Deciphering the functional diversity of the gut microbiota of the black soldier fly (Hermetia illucens): recent advances and future challenges

Bioconversion using insects is a promising strategy to convert organic waste (catering leftovers, harvest waste, food processing byproducts, etc.) into biomass that can be used for multiple applications, turned into high added-value products, and address environmental, societal and economic concerns. Due to its ability to feed on a tremendous variety of organic wastes, the black soldier fly (Hermetia illucens) has recently emerged as a promising insect for bioconversion of organic wastes on an industrial scale. A growing number of studies have highlighted the pivotal role of the gut microbiota in the performance and health of this insect species. This review aims to provide a critical overview of current knowledge regarding the functional diversity of the gut microbiota of H. illucens, highlighting its importance for bioconversion, food safety and the development of new biotechnological tools. After providing an overview of the different strategies that have been used to outline the microbial communities of H. illucens, we discuss the diversity of these gut microbes and the beneficial services they can provide to their insect host. Emphasis is placed on technical strategies and aspects of host biology that require special attention in the near future of research. We also argue that the singular digestive capabilities and complex gut microbiota of H. illucens make this insect species a valuable model for addressing fundamental questions regarding the interactions that insects have evolved with microorganisms. By proposing new avenues of research, this review aims to stimulate research on the microbiota of a promising insect to address the challenges of bioconversion, but also fundamental questions regarding bacterial symbiosis in insects.

Lactobacillus casei-derived postbiotics inhibited digestion of triglycerides, glycerol phospholipids and sterol lipids via allosteric regulation of BSSL, PTL and PLA2 to prevent obesity: perspectives on deep learning integrated multi-omics

The anti-obesity potential of probiotics has been widely reported, however their utilization in high-risk patients and potential adverse reactions have led researchers to focus their attention on postbiotics. Herein, pseudo-targeted lipidomics linked with deep learning-based metabolomics was utilized to dynamically characterize the postbiotic potential of heat-inactivated Lactobacillus casei JCM1134 supplementation after a high-fat diet in treating obesity. MG (ranged from 423.0 ± 1.4 mg L-1 to 331.45 ± 2.3 mg L-1), LPC (ranged from 13.1 ± 0.08 mg L-1 to 10.2 ± 0.1 mg L-1) and Cho (ranged from 9.0 ± 0.3 mg L-1 to 5.7 ± 0.2 mg L-1) in intestinal digestive products were significantly decreased, indicating that the digestion of lipid was inhibited. 8-C-glucosylorobol, from Lactobacillus casei, was confirmed from quantitative results and molecular simulation calculations to inhibit the transformation of TG, DG, and ChE through weakening hydrogen bonds between enzymes and substrates and reducing the binding energy. Pristimerin and 2,4-quinolinediol can effectively reduce the hydrogen bonding force between PC and phospholipase A2, which were related to the obstruction of phosphatidylcholine digestion. This research deepened the understanding of the mechanism underlying the inactivated probiotics affecting lipid digestion, establishing the critical groundwork for clinical application of probiotics in inhibiting obesity.

Experimental study on pollution release and sediment scouring of sewage sediment in a drainage pipe considering incubation time

The pollution release and the antiscourability characteristics of pipe sewage sediments can directly determine the blockage status of pipelines and the treatment burden at the outflow (sewage treatment plant). In this study, sewer environments with different burial depths were designed to explore the impact of incubation time on microbial activity, and the impacts of microbial activity on the physicochemical characteristics, pollution release effect and antiscouring ability of the silted sediment in the drainage pipe were further explored. The results showed that the incubation time, sediment matrix, temperature and dissolved oxygen affected microbial activity, but temperature had a greater influence. These factors affected microbial activity and loosened the superstructure in the sediment. In addition, by measuring the indices of nitrogen and phosphorus in the overlying water, it was found that sediment incubated for a certain time released pollutants into the overlying water, and the release amount was obviously affected by high temperature (e.g. 35 ℃). After a certain time (e.g. 30 days), biofilms appeared on the sediment surface, and the antiscourability of sediment was significantly improved, which was reflected in the increase in the median particle size of sediment left in the pipe.

Electric-Inducive Microbial Interactions in a Thermophilic Anaerobic Digester Revealed by High-Throughput Sequencing of Micron-Scale Single Flocs

Although conductive materials have been shown to improve efficiency in anaerobic digestion (AD) by modifying microbial interactions, the interacting network under thermophilic conditions has not been examined. To identify the true taxon-taxon associations within thermophilic anaerobic digestion (TAD) microbiome and reveal the influence of carbon cloth (CC) addition, we sampled micron-scale single flocs (40-70 μm) randomly isolated from lab-scale thermophilic digesters. Results revealed that CC addition not only significantly boosted methane yield by 25.3% but also increased the spatial heterogeneity of the community in the sludge medium. After CC addition, an evident translocation of Pseudomonas from the medium to the biofilm was observed, showing their remarkable capacity for biofilm formation. Additionally, Clostridium and Thermotogaceae tightly aggregated and steadily co-occurred in the medium and biofilm of the TAD microbiome, which might be associated with their unique extracellular sugar metabolizing style. Finally, CC induced syntrophic interaction between Syntrophomonas and denitrifiers of Rhodocyclaceae. The upregulated respiration-associated electron transferring genes (Cyst-c, complex III) on the cellular membranes of these collaborating partners indicated a potential coupling of the denitrification pathway with syntrophic acetate oxidation via direct interspecies electron transfer (DIET). These findings provide an insight into how conductive materials promote thermophilic digestion performance and open the path for improved community monitoring of biotreatment systems.

Variations in antibiotic resistance genes and microbial community in sludges passing through biological nutrient removal and anaerobic digestion processes in municipal wastewater treatment plants

Antimicrobial resistance (AMR) represents a relentless, silent pandemic. Contributing to this are wastewater treatment plants (WWTPs), a potential source of antibiotic resistance genes' (ARGs) transmission to the environment, threatening public health. The presence of ARGs in pathogenic bacteria and their release into the environment by WWTPs threatens the public health. The current study investigated changes in ARGs' abundance in biological nutrient removal (BNR) processes and anaerobic digestion (AD) reactors of two WWTPs. Also, microbial community structure, which is known to shape the distribution and abundance of ARGs, was also analyzed. The relative abundance of eight ARGs (tetX, tetA, tetM, TEM, sul1, sul2, ermB and qnrD) was quantified as ARGs' copies/16 S rRNA gene copies using quantitative polymerase chain reaction (qPCR). Microbial community composition was assessed by 16 S rRNA microbiome sequencing analysis. TetX was prevalent among the eight ARGs, followed by TEM and sul1. However, its abundance was decreased in the AD sludges compared to BNR sludges. Proteobacteria was the major bacterial phylum found in all the sludge samples, while Arcobacter, 12up and Acidovorax were the predominant genera. Acinetobacter and Flavobacterium were significantly more abundant in the BNR sludges, while 12up and Aeromonas were predominant in AD sludges. Principal component analysis (PCA) revealed a clear difference in dominant ARGs and bacteria between the sludges in the processes of BNR and AD of the two WWTPs. Clinically relevant bacterial genera, Klebsiella and Enterococcus, found in both the BNR and AD sludges, were significantly correlated with the tetX gene. Throughout this study, the relationship between microbial communities and specific ARGs was revealed, illustrating that the composition of the microbial community could play a vital role in the abundance of ARGs. These results will better inform future studies aimed at controlling the spread of ARGs and their potential hosts from WWTPs.

Energy-Efficient AnMBRs Technology for Treatment of Wastewaters: A Review

In recent years, anaerobic membrane bioreactor (AnMBRs) technology, a combination of a biological reactor and a selective membrane process, has received increasing attention from both industrialists and researchers. Undoubtedly, this is due to the fact that AnMBRs demonstrate several unique advantages. Firstly, this paper addresses fundamentals of the AnMBRs technology and subsequently provides an overview of the current state-of-the art in the municipal and domestic wastewaters treatment by AnMBRs. Since the operating conditions play a key role in further AnMBRs development, the impact of temperature and hydraulic retention time (HRT) on the AnMBRs performance in terms of organic matters removal is presented in detail. Although membrane technologies for wastewaters treatment are known as costly in operation, it was clearly demonstrated that the energy demand of AnMBRs may be lower than that of typical wastewater treatment plants (WWTPs). Moreover, it was indicated that AnMBRs have the potential to be a net energy producer. Consequently, this work builds on a growing body of evidence linking wastewaters treatment with the energy-efficient AnMBRs technology. Finally, the challenges and perspectives related to the full-scale implementation of AnMBRs are highlighted.

Biogas Production and Microbial Communities of Mesophilic and Thermophilic Anaerobic Co-Digestion of Animal Manures and Food Wastes in Costa Rica

Biomass generated from agricultural operations in Costa Rica represents an untapped renewable resource for bioenergy generation. This study investigated the effects of two temperatures and three mixture ratios of manures and food wastes on biogas production and microbial community structure. Increasing the amount of fruit and restaurant wastes in the feed mixture significantly enhanced the productivity of the systems (16% increase in the mesophilic systems and 41% in the thermophilic). The methane content of biogas was also favored at higher temperatures. Beta diversity analysis, based on high-throughput sequencing of 16S rRNA gene, showed that microbial communities of the thermophilic digestions were more similar to each other than the mesophilic digestions. Species richness of the thermophilic digestions was significantly greater than the corresponding mesophilic digestions (F = 40.08, p = 0.003). The mesophilic digesters were dominated by Firmicutes and Bacteroidetes while in thermophilic digesters, the phyla Firmicutes and Chloroflexi accounted for up to 90% of all sequences. Methanosarcina represented the key methanogen and was more abundant in thermophilic digestions. These results demonstrate that increasing digestion temperature and adding food wastes can alleviate the negative impact of low C:N ratios on anaerobic digestion.

Ontology-aware deep learning enables ultrafast and interpretable source tracking among sub-million microbial community samples from hundreds of niches

The taxonomic structure of microbial community sample is highly habitat-specific, making source tracking possible, allowing identification of the niches where samples originate. However, current methods face challenges when source tracking is scaled up. Here, we introduce a deep learning method based on the Ontology-aware Neural Network approach, ONN4MST, for large-scale source tracking. ONN4MST outperformed other methods with near-optimal accuracy when source tracking among 125,823 samples from 114 niches. ONN4MST also has a broad spectrum of applications. Overall, this study represents the first model-based method for source tracking among sub-million microbial community samples from hundreds of niches, with superior speed, accuracy, and interpretability. ONN4MST is available at https://github.com/HUST-NingKang-Lab/ONN4MST.

Synergistic Effect of Magnetite and Bioelectrochemical Systems on Anaerobic Digestion

Conventionally, the anaerobic digestion of industrial effluent to biogas constitutes less than 65% methane, which warrants its potential methanation to mitigate carbon dioxide and other anthropogenic gas emissions. The performance of the anaerobic digestion process can be enhanced by improving biochemical activities. The aim of this study was to examine the synergistic effect of the magnetite and bioelectrochemical systems (BES) on anaerobic digestion by comparing four digesters, namely a microbial fuel cell (MFC), microbial electrolysis cell (MEC), MEC with 1 g of magnetite nanoparticles (MECM), and a control digester with only sewage sludge (500 mL) and inoculum (300 mL). The MFC digester was equipped with zinc and copper electrodes including a 100 Ω resistor, whereas the MEC was supplied with 0.4 V on the electrodes. The MECM digester performed better as it improved microbial activity, increased the content of methane (by 43% compared to 41% of the control), and reduced contaminants (carbon oxygen demand, phosphates, colour, turbidity, total suspended solids, and total organic carbon) by more than 81.9%. Current density (jmax = 25.0 mA/m²) and electrical conductivity (275 µS/cm) were also high. The prospects of combining magnetite and bioelectrochemical systems seem very promising as they showed a great possibility for use in bioelectrochemical methane generation and wastewater treatment.

Effect of temperature on the persistence of fecal bacteria in ambient anaerobic digestion systems treating swine manure

This study aimed to explore the effect of temperature on the persistence of fecal bacteria by multiple approaches in ambient anaerobic digestion systems treating swine manure. Both lab-scale (15 °C, 20 °C, and 25 °C) and field (26 °C on average) studies were conducted by high-throughput sequencing and culture-based methods. A community-wide Bayesian SourceTracker method was used to identify and estimate the fecal bacterial proportion in anaerobic effluent. High proportional contributions of fecal bacteria were observed in effluent at 15 °C (73%) and 20 °C (75%), while less was found at 25 °C (19%). This was further verified by a field study (23%) and an anaerobic reactor study at 37 °C (0.01%). To explore the potential reasons for differences in fecal bacterial proportions, bacterial taxa were divided into "lost" and "survivor" taxa in manure waste by LEfSe. The "survivor" taxa abundance was positively correlated with SourceTracker proportion (r = 0.913, P = 0.001), but negatively correlated with temperature (r = -0.826, P = 0.006). In addition, biomarkers in effluent were divided into "enriched" and "de novo" taxa. "Enriched" taxa, including acidogenic and acetogenic bacteria, were found at all temperatures, whereas taxa related to organic degradation were multiplied "de novo" at 25 °C. Variation partition analysis showed that temperature could explain 30% of variations in effluent bacterial community. Moreover, coliforms isolated from the manure and effluents at 15 °C and 20 °C were also phylogenetically related. This study provided comprehensive insight into the impact of temperature on the persistence of fecal bacteria in anaerobic effluent, with temperatures over 25 °C recommended to reduce fecal pollution.

Studying Microbial Communities through Co-Occurrence Network Analyses during Processes of Waste Treatment and in Organically Amended Soils: A Review

Organic wastes have the potential to be used as soil organic amendments after undergoing a process of stabilization such as composting or as a resource of renewable energy by anaerobic digestion (AD). Both composting and AD are well-known, eco-friendly approaches to eliminate and recycle massive amounts of wastes. Likewise, the application of compost amendments and digestate (the by-product resulting from AD) has been proposed as an effective way of improving soil fertility. The study of microbial communities involved in these waste treatment processes, as well as in organically amended soils, is key in promoting waste resource efficiency and deciphering the features that characterize microbial communities under improved soil fertility conditions. To move beyond the classical analyses of metataxonomic data, the application of co-occurrence network approaches has shown to be useful to gain insights into the interactions among the members of a microbial community, to identify its keystone members and modelling the environmental factors that drive microbial network patterns. Here, we provide an overview of essential concepts for the interpretation and construction of co-occurrence networks and review the features of microbial co-occurrence networks during the processes of composting and AD and following the application of the respective end products (compost and digestate) into soil.

Recent advances in methanogenesis through direct interspecies electron transfer via conductive materials: A molecular microbiological perspective

Conductive materials can serve as biocatalysts during direct interspecies electron transfer for methanogenesis in anaerobic reactors. However, the mechanism promoting direct interspecies electron transfer in anaerobic reactors, particularly under environments in which diverse substrates and microorganisms coexist, remains to be elucidated from a scientific or an engineering point of view. Currently, many molecular microbiological approaches are employed to understand the fundamentals of this phenomenon. Here, the direct interspecies electron transfer mechanisms and relevant microorganisms identified to date using molecular microbiological methods were critically reviewed. Moreover, molecular microbiological methods for direct interspecies electron transfer used in previous studies and important findings thus revealed were analyzed. This review will help us better understand the phenomena of direct interspecies electron transfer using conductive materials and offer a framework for future molecular microbiological studies.

A multidimensional perspective on microbial interactions

Beyond being simply positive or negative, beneficial or inhibitory, microbial interactions can involve a diverse set of mechanisms, dependencies and dynamical properties. These more nuanced features have been described in great detail for some specific types of interactions, (e.g. pairwise metabolic cross-feeding, quorum sensing or antibiotic killing), often with the use of quantitative measurements and insight derived from modeling. With a growing understanding of the composition and dynamics of complex microbial communities for human health and other applications, we face the challenge of integrating information about these different interactions into comprehensive quantitative frameworks. Here, we review the literature on a wide set of microbial interactions, and explore the potential value of a formal categorization based on multidimensional vectors of attributes. We propose that such an encoding can facilitate systematic, direct comparisons of interaction mechanisms and dependencies, and we discuss the relevance of an atlas of interactions for future modeling and rational design efforts.

Biostimulation of sewage sludge solubilization and methanization by hyper-thermophilic pre-hydrolysis stage and the shifts of microbial structure profiles

This study evaluated the influence of hyper-thermophilic pre-hydrolysis stage (70 °C) on methane recovery of sewage sludge at 35 °C. In this configuration, the process performance in both temperatures were estimated and the microbial communities were characterized by full-length16S rRNA genes and/or microbial activities. In addition, the appropriate solubilization reaction time was assessed. The results revealed that the higher hydrolysis and acidogenesis activities were achieved with longer reaction time of pretreatment (5 days) and thus higher organic nitrogen conversion and alkalinity were attained. Under appropriate pretreatment reaction time, pretreated sludge was characterized by 65% higher organic matters solubilization and 1.4-fold higher volatile fatty acids (VFAs) concentration compared to raw sludge. The overall methane yield produced under this scenario was 179 L CH₄. KgVS_in, with 15% of the absolute yield was produced in hydrolysis reactor. 50% reduction in bacteria belong to Firmicurtes was observed at mesophilic reactor and meanwhile the relative abundance of Bacteroidetes and Cloacimonetes were enhanced. The predominant methanogens in both stages did not change implying adaptation of Methanothermobacter (>62%) to mesophilic condition. However, increasing acetoclastic methanogens up to 30% in mesophilic reactor indicating methane was produced from pretreated sludge mainly through H₂- mediated CO₂ reduction and partially from acetate cleavage. The results highlight the key role of hyper-thermophilic pre-hydrolysis stage for better stabilization of sewage sludge without further investments in current biogas plants.

Microbial community response to ammonia levels in hydrogen assisted biogas production and upgrading process

Biological conversion of carbon dioxide into methane using hydrogen derived from surplus renewable energy (wind power) as reducing power is a novel technology for biogas upgrading. High ammonia concentrations are toxic to the biogas upgrading process, however the mechanisms behind the inhibition as well as the microbial stress response in such unique upgrading system have never been reported. Thus, the effect of high ammonia concentrations on microbial community during hydrogen induced biogas upgrading process was evaluated here. The results showed that a change from aceticlastic pathway to hydrogenotrophic pathway occurred when ammonia level increased (1-7 g NH₄⁺-N L^-1). In addition, the bacteria, potentially syntrophic associated with hydrogenotrophic methanogens, were enriched at high ammonia concentrations. Moreover, growth of some bacteria (e.g., Halanaerobiaceaeen and Leucobacter) which were vulnerable to ammonia toxicity was restored upon hydrogen injection. Furthermore, hydrogen injection under high ammonia concentration could promote growth of some hydrolytic and fermentative bacteria.

Influences of Temperature and Substrate Particle Content on Granular Sludge Bed Anaerobic Digestion

Influences of temperature (25–35 °C) and substrate particulate content (3.0–9.4 g total suspended solids (TSS)/L) on granular sludge bed anaerobic digestion (AD) were analyzed in lab-scale reactors using manure as a substrate and through modeling. Two particle levels were tested using raw (RF) and centrifuged (CF) swine manure slurries, fed into a 1.3-L lab-scale up-flow anaerobic sludge bed reactor (UASB) at temperatures of 25 °C and 35 °C. Biogas production increased with temperature in both high- and low-particle-content substrates; however, the temperature effect was stronger on high-particle-content substrate. RF and CF produced a comparable amount of biogas at 25 °C, suggesting that biogas at this temperature came mainly from the digestion of small particles and soluble components present in similar quantities in both substrates. At 35 °C, RF showed significantly higher biogas production than CF, which was attributed to increased (temperature-dependent) disintegration of larger solid particulates. Anaerobic Digestion Model No.1 (ADM1) based modeling was carried out by separating particulates into fast and slow disintegrating fractions and introducing temperature-dependent disintegration constants. Simulations gave a better fit for the experimental data than the conventional ADM1 model.

Ammonia stress on a resilient mesophilic anaerobic inoculum: Methane production, microbial community, and putative metabolic pathways

Short term inhibition tests, 16S rRNA tag sequencing and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt), were employed to visualise the effects of increasing total ammoniacal nitrogen (TAN) concentration (3400-10166 ppm TAN) on microbial community structure and metabolic pathways for acetate degradation. The rate of methane production on acetate was significantly reduced by TAN concentrations above 6133 ppm; however, methane continued to be produced, even at 10166 ppm TAN (0.026 ± 0.0003 gCOD.gVS^-1_inoculum.day^-1). Hydrogenotrophic methanogenesis with syntrophic acetate oxidation (SAO) was identified as the dominant pathway for methane production. A shift towards SAO pathways at higher TAN concentrations and a decrease in the number of 'gene hits' for key genes in specific methanogenesis pathways was observed. Overall, the results highlighted potential for inhibition activity testing to be used together with PICRUSt, to estimate changes in microbial metabolism and to better understand microbial resilience in industrial AD facilities.

Exploring the roles of and interactions among microbes in dry co-digestion of food waste and pig manure using high-throughput 16S rRNA gene amplicon sequencing

BACKGROUND

With the increasing global population and increasing demand for food, the generation of food waste and animal manure increases. Anaerobic digestion is one of the best available technologies for food waste and pig manure management by producing methane-rich biogas. Dry co-digestion of food waste and pig manure can significantly reduce the reactor volume, capital cost, heating energy consumption and the cost of digestate liquid management. It is advantageous over mono-digestion of food waste or pig manure due to the balanced carbon/nitrogen ratio, high pH buffering capacity, and provision of trace elements. However, few studies have been carried out to study the roles of and interactions among microbes in dry anaerobic co-digestion systems. Therefore, this study aimed to assess the effects of different inocula (finished digestate and anaerobic sludge taken from wastewater treatment plants) and substrate compositions (food waste to pig manure ratios of 50:50 and 75:25 in terms of volatile solids) on the microbial community structure in food waste and pig manure dry co-digestion systems, and to examine the possible roles of the previously poorly described bacteria and the interactions among dry co-digestion-associated microbes.

RESULTS

The dry co-digestion experiment lasted for 120 days. The microbial profile during different anaerobic digestion stages was explored using high-throughput 16S rRNA gene amplicon sequencing. It was found that the inoculum factor was more significant in determining the microbial community structure than the substrate composition factor. Significant correlation was observed between the relative abundance of specific microbial taxa and digesters' physicochemical parameters. Hydrogenotrophic methanogens dominated in dry co-digestion systems.

CONCLUSIONS

The possible roles of specific microbial taxa were explored by correlation analysis, which were consistent with the literature. Based on this, the anaerobic digestion-associated roles of 11 bacteria, which were previously poorly understood, were estimated here for the first time. The inoculum played a more important role in determining the microbial community structure than substrate composition in dry co-digestion systems. Hydrogenotrophic methanogenesis was a significant methane production pathway in dry co-digestion systems.

Temperature shapes the microbiota in anaerobic digestion and drives efficiency to a maximum at 45 °C

Throwing longstanding habits over the pile may be necessary to improve biogas production, in particular when it comes to the process temperature. Its effect on biogas production was investigated with lab-scale reactors operated in fed-batch mode (cattle slurry and maize straw) at 10-55 °C over six months. Biochemical and microbial changes were comprehensively investigated. Production was highest and most efficient at 45 °C with an average methane yield of 166 NL kg^-1 VS, and thus 12.8% and 9.6% higher than at 37 and 55 °C. Temperature significantly affected the microbiota and higher temperature provoked a shift from Bacteroidetes/Proteobacteria to Firmicutes. A transition from hydrogenotrophic to acetoclastic methanogenesis was observed from 10 to 45 °C, while the trend was reversed at 55 °C. The results contest the textbook notion of preferred and most efficient temperatures for AD and suggest reconsideration of the temperature range around 45 °C for efficient manure-based co-fermentation.

Comprehensive analysis of microbial communities in full-scale mesophilic and thermophilic anaerobic digesters treating food waste-recycling wastewater

Microbes were sampled for a year in a full-scale mesophilic anaerobic digester (MD) and a thermophilic anaerobic digester (TD) treating food waste-recycling wastewater (FRW), then microbial community structure, dynamics and diversity were quantified. In the MD, Fastidiosipila, Petrimonas, vadinBC27, Syntrophomonas, and Proteiniphilum were dominant bacterial genera; they may contribute to hydrolysis and fermentation. In the TD, Defluviitoga, Gelria and Tepidimicrobium were dominant bacteria; they may be responsible for hydrolysis and acid production. In the MD, dominant methanogens changed from Methanobacterium (17.1 ± 16.9%) to Methanoculleus (67.7 ± 17.8%) due to the increase in ammonium concentration. In the TD, dominant methanogens changed from Methanoculleus (42.8 ± 13.6%) to Methanothermobacter (49.6 ± 11.0%) due to the increase of pH. Bacteria and archaea were more diverse in the MD than in the TD. These results will guide development of microbial management methods to improve the process stability of MD and TD treating FRW.

Temperature regulates deterministic processes and the succession of microbial interactions in anaerobic digestion process

Temperature plays crucial roles in microbial interactions that affect the stability and performance of anaerobic digestion. In this study, the microbial interactions and their succession in the anaerobic digestion process were investigated at three levels, represented by (1) present and (2) active micro-organisms, and (3) gene expressions under a temperature gradient from 25 to 55 °C. Network topological features indicated a global variation in microbial interactions at different temperatures. The variations of microbial interactions in terms of network modularity and deterministic processes based on topological features, corresponded well with the variations of methane productions, but not with temperatures. A common successional pattern of microbial interactions was observed at different temperatures, which showed that both deterministic processes and network modularity increased over time during the digestion process. It was concluded that the increase in temperature-mediated network modularity and deterministic processes on shaping the microbial interactions improved the stability and efficiency of anaerobic digestion process.

In-situ sludge pretreatment in a single-stage anaerobic digester

This study aimed to develop an in-situ sludge pretreatment method by increasing the temperature from thermophilic to extreme thermophilic condition in a single-stage anaerobic digester. The results revealed that a stable performance was obtained within the temperature range of 55-65°C, and the maximum methane yield of 208.51±13.66mL/g VS was obtained at 65°C. Moreover, the maximum extent of hydrolysis (33%) and acidification (27.1%) was also observed at 65°C. However, further increase of temperature to 70°C did not improve the organic conversion efficiency. Microbial community analysis revealed that Coprothermobacter, highly related to acetate oxidisers, appeared to be the abundant bacterial group at higher temperature. A progressive shift in methanogenic members from Methanosarcina to Methanothermobacter was observed upon increasing the temperature. This work demonstrated single-stage sludge digestion system can be successfully established at high temperature (65°C) with stable performance, which can eliminate the need of conventional thermophilic pretreatment step.

The Hybrid Strategy of Thermoactinospora rubra YIM 77501T for Utilizing Cellulose as a Carbon Source at Different Temperatures

Thermoactinospora rubra YIM 77501^T is an aerobic, Gram-positive, spore-forming and cellulose degrading thermophilic actinomycete isolated from a sandy soil sample of a volcano. Its growth temperature range is 28–60°C. The genomic sequence of this strain revealed that there are 27 cellulase genes belonging to six glycoside hydrolase families. To understand the strategy that this strain uses to utilize carbon sources such as cellulose at different temperatures, comparative transcriptomics analysis of T. rubra YIM 77501^T was performed by growing it with cellulose (CMC) and without cellulose (replaced with glucose) at 30, 40, and 50°C, respectively. Transcriptomic analyses showed four cellulase genes (TrBG2, TrBG3, TrBG4, and ThrCel6B) were up-regulated at 30, 40, and 50°C. The rate of gene expression of TrBG2, TrBG3, TrBG4, and ThrCel6B were 50°C > 30°C > 40°C. One cellulase gene (TrBG1) and two cellulase genes (TrBG5 and ThrCel6A) were up-regulated only at 30 and 50°C, respectively. These up-regulated cellulase genes were cloned and expressed in Escherichia coli. The enzymatic properties of up-regulated cellulases showed a variety of responses to temperature. Special up-regulated cellulases TrBG1 and ThrCel6A displayed temperature acclimation for each growth condition. These expression patterns revealed that a hybrid strategy was used by T. rubra to utilize carbon sources at different temperatures. This study provides genomic, transcriptomics, and experimental data useful for understanding how microorganisms respond to environmental changes and their application in enhancing cellulose hydrolysis for animal feed and bioenergy production.