Impacts of environmental factors on microbial diversity, distribution patterns and syntrophic correlation in anaerobic processes

Resilience and response of anaerobic digestion systems to short-term hydraulic loading shocks: Focusing on total and active microbial community dynamics

Anaerobic digestion is known to be sensitive to operational changes, such as hydraulic loading shock, yet the impact on the microbiome, particularly the active RNA-based community, has not been fully understood. This study aimed to investigate the performance of anaerobic reactors and their microbial communities under short-term hydraulic loading shocks. Using synthetic wastewater, the reactor was subjected to 24-h shocks at three-fold and seven-fold the baseline loading rate, followed by DNA and RNA analyses to assess the system's resiliency and microbial responses. The research focused on shifts in major microbial groups and their functions, paying close attention to the active RNA community during loading shock events to better reflect the system's immediate condition. Findings indicated that although the microbial community structure, particularly among the archaea, was altered, the reactor quickly regained its balance. Differences were observed between DNA and RNA profiles and between regular and shock loadings; however, the alpha diversity and functions of the overall community were sustained. This study offers important insights for the design and operation of wastewater treatment plants, with the goal of achieving stable and efficient anaerobic digestion systems.

Soil microbiota plays a key regulatory role in the outbreak of tobacco root rot

Introduction

Root rot caused by the fungal pathogen Fusarium sp. poses significant challenges to tobacco cultivation in China, leading to major economic setbacks. The interplay between this pathogen and the wider soil microbial community remains poorly understood.

Methods

High-throughput sequencing technology was utilized to evaluate soil prokaryotic, fungal, and protistan communities. We compared microbial communities in infected soils to those in healthy soils from the same field. Additionally, the influence of pH on the microbial communities was assessed.

Results

Infected soils displayed elevated levels of soil nutrients but diminished observed richness across prokaryotic, fungal, and protistan groups. The pathogenic fungi Fusarium solani f sp. eumartii's abundance was notably increased in infected soils. Infection with F. solani significantly altered the soil's microbial community structure and interactions, manifested as a decrease in network scale and the number of keystone species. An evaluation of prokaryotes' role in F. solani's invasion revealed an increased number of connecting nodes in infected soils. Additionally, relationships between predatory protists and fungi were augmented, whereas predation on F. solani declined.

Discussion

The study underscores the significance of comprehending the interactions among soil microorganisms and brings to light the susceptibility of soil microbial communities to pathogen invasion. It offers insights into the multifaceted relationships and potential vulnerabilities within the soil ecosystem in the context of Fusarium sp. invasion.

Simulation of Denitrification Process of Calcium Nitrate Combined with Low Oxygen Aeration Based on Double Logarithm Mode

In situ remediation of sediment pollution is an important measure for the treatment of urban black-odorous water. In this study, the process of calcium nitrate dosing and low oxygen aeration was used to repair the sediment of black-odorous water body in a glass container. The variation trend and removal efficiency of ammonia nitrogen and nitrate nitrogen in sediment and overlying water were investigated during the process. By establishing the double logarithm model of calcium nitrate sediment repair process, the change law of ammonia nitrogen and nitrate nitrogen content in sediment under different calcium nitrate dosing conditions was studied, and the denitrification process of different calcium nitrate dosing and low oxygen aeration was simulated. The results showed that by establishing the double logarithm model of calcium nitrate sediment remediation process, when the dosage of calcium nitrate was 6%, the inhibition rate of calcium nitrate on nitrate nitrogen release was the largest. The stable inhibitory concentration of nitrate nitrogen was 11.65 mg/g, and the stable inhibited concentration of ammonia nitrogen was 382.95 mg/kg. The stable inhibitory concentration of nitrate nitrogen and ammonia nitrogen in overlying water was 8.34 mg/L and 16.47 mg/L. Moreover, excessive calcium nitrate (8%) may increase the risk of microbial ecological environment in sediment and weaken the inhibitory effect. The optimum parameters were the calcium nitrate dosage of 6%, the reaction time of 21 days, and the aeration rate of 30 mL/min. Under these conditions, the removal effect of ammonia nitrogen in sediment and overlying water was further improved, and the concentration of nitrate nitrogen was effectively controlled. The stable inhibitory content of nitrate nitrogen in sediment was 5.55 mg/g, and the stable inhibitory content of ammonia nitrogen was 982.79 mg/kg. The stable inhibitory concentration of nitrate nitrogen and ammonia nitrogen in overlying water was 6.55 mg/L and 118.20 mg/L. Based on a simulation, this study provides important technical support for the formulation of a refined endogenous pollution control scheme by controlling the process of calcium nitrate remediation and low oxygen aeration.

Roles of granular activated carbon (GAC) and operational factors on active microbiome development in anaerobic reactors

Ambient temperature municipal sewage was treated using two laboratory-scale up-flow anaerobic sludge blanket reactors for 225 days. Granular activated carbon (GAC) was added to one reactor to facilitate the development of direct interspecies electron transfer (DIET). The GAC addition increased total chemical oxygen demand removal by 5% - 18%. In addition to assessing the relative abundance of active amplicon sequence variants (ASVs), the mass balance model, the Mantel test, and the generalized linear models were applied to evaluate the dynamics of the active ASVs and the key operational factors controlling the bioreactor microbial community. These results demonstrated that, in addition to the GAC addition, extrinsic engineering operational factors played important roles in controlling (active) microbial communities. This study underlines the importance of taking a wholistic approach to assess microbial population dynamics. Reactor design and performance prediction should consider key engineering parameters when using DIET-based AD reactors in the future.

Coupling oxidation of acid volatile sulfide, ferrous iron, and ammonia nitrogen from black-odorous sediment via autotrophic denitrification-anammox by nitrate addition

The coupling removal of acid volatile sulfide (AVS), ferrous iron, and ammonia nitrogen has been applied for black-odorous sediment remediation. In this study, calcium nitrate with different N/(S + Fe) ratios (0.45, 0.90, 1.20 and 1.80) was added into black-odorous sediment in four systems named R1, R2, R3, and R4. Results showed that the removal rate of AVS was 76.40% in the R1, which was lower compared with rates in R2-R4 around 96.70%. The ferrous oxidation rate was approximately 87.00% in R2-R4, which was considerably higher than that in the R1 (24.62%). And the ammonia was reduced by 81.02%, 88.00%, 100%, and 57.18% in R1, R2, R3 and R4, respectively. During the reaction, nitrite accumulation was observed, indicating partial denitrification. Moreover, microbes related to autotrophic denitrification (e.g., genus Thiobacillus, Dok59, GOUTA19, Gallionella, with the highest abundance of 15.40%, 13.21%, 8.79%, 9.44%, respectively) were detected in all systems. Furthermore, the anammox bacteria Candidatus_Brocadia with the highest abundance of 3.44% and 4.00% in R2 and R3, respectively was also found. These findings confirmed that AVS, ferrous iron, and ammonia nitrogen could be simultaneously removed via autotrophic denitrification coupled with anammox in black-odorous sediment by nitrate addition.

New insights into the effect of ethanol and volatile fatty acids proportions on methanogenic activities and pathways

During anaerobic digestion, methanogenic activities and pathways can be affected by intermediates. Here, the effects of intermediates acetate, propionate, and ethanol on methanogenesis were investigated. Four anaerobic sequencing batch reactors were acclimated with propionate (ASBR_P), ethanol/propionate (ASBR_EP), acetate/propionate (ASBR_AP), and ethanol/acetate/propionate (ASBR_EAP). Ethanol was the easiest one to be biodegraded, thereby enhancing the maximum methane production rate and shortening the lag phase, while the longest acclimation time and lowest methane production rate were observed in ASBR_P. Different microbial communities and syntrophic patterns existed in four reactors. Desulfovibrio and Geobacter were the dominant ethanol-oxidizing bacteria in ASBR_EP and ASBR_EAP, respectively. Both Desulfovibrio and Geobacter possessed the potential of extracellular electron transfer, which might be the advantage of ethanol dosage for enhancing methanogenesis through direct interspecies electron transfer. Methanosarcina was enriched in ASBR_P and ASBR_AP, while Methanosaeta in ASBR_EP and ASBR_EAP. Genes responsible for acetoclastic methanogenesis were significantly enriched in ASBR_EAP, possibly resulting in the highest methanogenic activity from acetate. Results from this study will advance the optimization of practical anaerobic systems, which can be achieved by regulating the intermediates with different fermenting pathways.

Coupled effects of ferroferric oxide supplement and ethanol co-metabolism on the methanogenic oxidation of propionate

Direct interspecies electron transfer (DIET) is a new electron-transfer strategy for enhanced propionate degradation. Ethanol can enrich the DIET species of Geobacter and conductive ferroferric oxide (Fe₃O₄) can promote DIET. Therefore, coupled effects of ethanol and Fe₃O₄ on propionate degradation were investigated. The maximum CH₄ production rate was increased by 81.4% by adding Fe₃O₄ when simultaneously fed with ethanol and propionate, while the improvement could not be observed without ethanol. The sludge conductivity and the electron transfer system activity by adding Fe₃O₄ were increased by 2.66 and 2.73 times, respectively. Besides, the relative abundance of functional microbes such as Geobacter, Syntrophobacter, Smithella, and Methanosaeta, and their functional genes were increased by the supplement of Fe₃O₄. The improvement of propionate degradation by adding Fe₃O₄ was largely attributed to the co-existence of ethanol degradation. The DIET between Geobacter and Methanosaeta might provide more energies or rapidly consume the oxidation products to promote the propionate degradation.

Spatial and seasonal variation of methanogenic community in a river-bay system in South China

River-bay system is a transitional zone connecting land and ocean and an important natural source for methane emission. Methanogens play important roles in the global greenhouse gas budget and carbon cycle since they produce methane. The abundance and community assemblage of methanogens in such a dynamic system are not well understood. Here, we used quantitative PCR and high-throughput sequencing of the mcrA gene to investigate the abundance and community composition of methanogens in the Shenzhen River-Bay system, a typical subtropical river-bay system in Southern of China, during the wet and dry seasons. Results showed that mcrA gene abundance was significantly higher in the sediments of river than those of estuary, and was higher in wet season than dry season. Sequences of mcrA gene were mostly assigned to three orders, including Methanosarcinales, Methanomicrobiales, and Methanobacteriales. Specifically, Methanosarcina, Methanosaeta, and Methanobacterium were the most abundant and ubiquitous genera. Methanogenic communities generally clustered according to habitat (river vs. estuary), and salinity was the major factor driving the methanogenic community assemblage. Furthermore, the indicator groups for two habitats were identified. For example, Methanococcoides, Methanoculleus, and Methanogenium preferentially existed in estuarine sediments, whereas Methanomethylovorans, Methanolinea, Methanoregula, and Methanomassiliicoccales were more abundant in riverine sediments, indicating distinct ecological niches. Overall, these findings reveal the distribution patterns of methanogens and expand our understanding of methanogenic community assemblage in the river-bay system. Key Points • Abundance of methanogens was relatively higher in riverine sediments. • Methanogenic community in estuarine habitat separated from that in riverine habitat. • Salinity played a vital role in regulating methanogenic community assemblage.