Revealing microbial community assembly patterns and succession process in the blackening process of black-odor water.

Human-imported pollutants could induce water black, changing microbial community structure and function. Employed 16S rRNA high-throughput sequencing, field-scale investigations and laboratory-scale experiments were successively conducted to reveal mechanistic insights into microbial community assembly and succession of black-odor waters (BOWs). In the field-scale investigation, livestock breeding wastewater (56.7 ± 3.2%) was the most critical microbial source. Moreover, fermentation (27.1 ± 4.4%) was found to be the dominant function. Combined with laboratory experiments, the critical environmental factors, such as total organic carbon (30-100 mg/L), ammonia nitrogen (2.5-9 mg/L), initial dissolved oxygen (2-8 mg/L) and chlorophyll a (0-90 mg/L), impacted the intensity of blackening. The differentiation of ecological niches within the microbial community played a significant role in driving the blackening speed. In laboratory-scale experiments, the microbial ecological niche determined the blackening timing and dominations of the stochastic processes in the microbial assembly process (88 - 51%). The three stages, including the anaerobic degradation stage, blackening stage and slow recovery stage, were proposed to understand the assembly of the microbial communities. These findings enhance our understanding of microorganisms in BOWs and provide valuable insights for detecting and managing heavily organic polluted waters.

Mitigated N2O emissions from submerged-plant-covered aquatic ecosystems on the Changjiang River Delta.

Submerged plants affect nitrogen cycling in aquatic ecosystems. However, whether and how submerged plants change nitrous oxide (N2O) production mechanism and emissions flux remains controversial. Current research primarily focuses on the feedback from N2O release to variation of substrate level and microbial communities. It is deficient in connecting the relative contribution of individual N2O production processes (i.e., the N2O partition). Here, we attempted to offer a comprehensive understanding of the N2O mitigation mechanism in aquatic ecosystems on the Changjiang River Delta according to stable isotopic techniques, metagenome-assembly genome analysis, and statistical analysis. We found that the submerged plant reduced 45 % of N2O emissions by slowing down the dissolved inorganic nitrogen conversion velocity to N2O in sediment (Vf-[DIN]sed). It was attributed to changing the N2O partition and suppressing the potential capacity of net N2O production (i.e., nor/nosZ). The dominated production processes showed a shift with increasing excess N2O. Meanwhile, distinct shift thresholds of planted and unplanted habitats reflected different mechanisms of stimulated N2O production. The hotspot zone of N2O production corresponded to high nor/nosZ and unsaturated oxygen (O2) in unplanted habitat. In contrast, planted habitat hotspot has lower nor/nosZ and supersaturated O2. O2 from photosynthesis critically impacted the activities of N2O producers and consumers. In summary, the presence of submerged plants is beneficial to mitigate N2O emissions from aquatic ecosystems.

The ecological role of microbiome at community-, taxonomic - and genome-levels in black-odorous waters.

Black-odorous waters (BOWs) are heavily polluted waters where microbial information remains elusive mechanistically. Based on gene amplicon and metagenomics sequencing, a comprehensive study was conducted to investigate the microbial communities in urban and rural BOWs. The results revealed that microbial communities' assembly in urban and rural BOWs was predominantly governed by stochastic factors at the community level. At the taxonomic level, there were 62 core species (58.48%) in water and 207 core species (44.56%) in sediment across urban and rural areas. Notably, significant differences were observed in the functional genetic composition of BOWs between urban and rural areas. Specifically, rural areas exhibited an enhanced abundance of genes involved in nitrogen fixation, Fe2+ transport, and sulfate reduction. Conversely, urban areas showed higher abundances of some genes associated with carbon fixation, nitrification and denitrification. A sulfur-centered ecological model of microbial communities was constructed by integrating data from the three levels of analysis, and 14 near-complete draft genomes were generated, representing a substantial portion of the microbial community (35.04% in rural BOWs and 29.97% in urban BOWs). This research provides significant insights into the sustainable management and preservation of aquatic ecosystems affected by BOWs.

Characterizing dissolved organic matter and bacterial community interactions in a river network under anthropogenic landcover.

Anthropogenic landcover could rise nutrient concentrations and impact the characteristics and bioavailability of dissolved organic matter (DOM) in a river network. Exploring the interactions between DOM and microbials might be conducive to revealing biogeochemistry behaviors of organic matter. In this study, synchronous fluorescence spectra (SFS) with Gaussian band fitting and two-dimensional correlation spectroscopy (2D-COS) were employed to identify DOM fractions and reveal their interactions with bacterial communities. DOM was extracted from a river network under eco-agricultural rural (RUR), eco-residential urban (URB), eco-economical town (TOW), and eco-industrial park (IND) regions in Jiashan Plain of eastern China. The overlapping peaks observed in the SFS were successfully separated into four fractions using Gaussian band fitting, i.e., tyrosine-like fluorescence (TYLF), tryptophan-like fluorescence (TRLF), microbial humic-like fluorescence (MHLF), and fulvic-like fluorescence (FLF) materials. Across all four regions, TRLF (44.79% ± 7.74%) and TYLF (48.09% ± 8.85%) were the dominant components. Based on 2D-COS, variations of TYLF and TRLF were extremely larger than those of FLF in RUR-TOW. However, in URB-IND, the former exhibited lower variations compared to the latter. These suggested that FLF be likely derived continuously from lignin and other residue of terrestrial plant origin along the river network, and TYLF and TRLF be originated discontinuously from domestic wastewater in RUR-TOW. By high-throughput sequenced OTUs, the number of organisms in RUR-TOW could be higher than those in URB-IND, while genes associated with carbohydrate metabolism were lower in former than those in the latter. According to co-occurrence networks, microbes could promote the production of TYLF and TRLF in RUR-TOW. In contrast, microbial communities in URB-IND might contribute to decompose FLF. The obtained results could not only reveal interactions between DOM fractions and bacterial communities in the river network, but this methodology may be applied to other water bodies from different landscapes.

Mechanistic insights into dissolved organic matter-driven protistan and bacterial community dynamics influenced by vegetation restoration.

Vegetation restoration projects can not only improve water quality by absorbing and transferring pollutants and nutrients from non-vegetation sources, but also protect biodiversity by providing habitat for biological growth. However, the mechanism of the protistan and bacterial assembly processes in the vegetation restoration project were rarely explored. To address this, based on 18 S rRNA and 16 S rRNA high-throughput sequencing, we investigated the mechanism of protistan and bacterial community assembly processes, environmental conditions, and microbial interactions in the rivers with (out) vegetation restoration. The results indicated that the deterministic process dominated the protistan and bacterial community assembly (94.29% and 92.38%), influenced by biotic and abiotic factors. For biotic factors, microbial network connectivity was higher in the vegetation zone (average degree = 20.34) than in the bare zone (average degree = 11.00). For abiotic factors, the concentration of dissolved organic carbon ([DOC]) was the most important environmental factor affecting the microbial community composition. [DOC] was lower significantly in vegetation zone (18.65 ± 6.34 mg/L) than in the bare zone (28.22 ± 4.82 mg/L). In overlying water, vegetation restoration upregulated the protein-like fluorescence components (C1 and C2) by 1.26 and 1.01-folds and downregulated the terrestrial humic-like fluorescence components (C3 and C4) by 0.54 and 0.55-folds, respectively. The different DOM components guided bacteria and protists to select different interactive relationships. The protein-like DOM components led to bacterial competition, whereas the humus-like DOM components resulted in protistan competition. Finally, the structural equation model was established to explain that DOM components can affect protistan and bacterial diversity by providing substrates, facilitating microbial interactions, and promoting nutrient input. In general, our study provides insights into the responses of vegetation restored ecosystems to the dynamics and interactives in the anthropogenically influenced river and evaluates the ecological restoration performance of vegetation restoration from a molecular biology perspective.

Bio-based carbon materials with multiple functional groups and graphene structure to boost methane production from ethanol anaerobic digestion.

This study evaluated the effects of bio-based carbon materials on methane production by anaerobic digestion. The results showed that biochar and hydrochar can promote cumulative methane yield by 15% to 29%. However, there was no statistical significance (p > 0.05) between hydrochar and biochar produced at different temperature on methane production. 16S rRNA gene sequencing and bioinformatics analysis showed that biochar and hydrochar enriched microorganism that might participate in direct interspecies electron transfer (DIET) such as Pseudomonadaceae, Bacillaceae, and Clostridiaceae. The the surface properties of the modified biochar were characterized with BET, Raman, FTIR and XPS. Bio-based carbon materials with uniform dispersion provided a stable environment for the DIET of microorganisms and electrons are transferred through aromatic functional groups on the surface of materials. This study reveals bio-based carbon materials surface properties on methane production in anaerobic digestion and provides a new approach to recycling spent coffee grounds.

Promoting potential direct interspecies electron transfer (DIET) and methanogenesis with nitrogen and zinc doped carbon quantum dots.

Although it has been demonstrated that one-dimensional, two-dimensional, and three-dimensional carbon nanomaterials can improve the CH4 production of anaerobic digestion (AD), the effect of zero-dimensional carbon nanomaterials on AD have not been reported. To expand the application of carbon nanomaterials in AD, the effect of zero-dimensional carbon nanomaterials-carbon quantum dots (CDs) on various feedstocks (c.a. cellulose, glucose, ethanol, and vinegar residue) were investigated in this study. Results have shown that CH4 yield from ethanol was increased by 24.59% (p = 0.396) after adding 5 g/L zinc doped carbon quantum dots (Zn-doped CDs) while that from vinegar residue was dramatically increased by 230% (p = 0.000) using 5 g/L nitrogen doped carbon quantum dots (N-doped CDs). In addition, photoluminescence demonstrated that CDs acted as a capacitor for transmitting and receiving electrons. Furthermore, co-occurrence network analysis revealed that Clostridiales might be used as a signal source to communicate with other species. This study firstly shifted the application of CDs from fluorescence to AD and manifested its positive impact on AD. In short, these findings provided a better understanding on the effects of CDs on different feedstocks of methanogenesis and revealed new evidence of stimulating methanogenesis via CDs.