Effects of micro-nano bubble water addition on maturation degree and microbial community during aerobic composting

In order to explore the effects of micro-nano bubble water (MNBW) on compost maturation and the microbial community in cow manure and straw during aerobic composting, we conducted composting tests using tap water with 12 mg/L (O12), 15 mg/L (O15), 18 mg/L (O18), and 21 mg/L (O21) dissolved oxygen in MNBW, as well as tap water with 9 mg/L dissolved oxygen as a control (CK). The results showed that O21 increased the maximum compost temperature to 64 °C, which was higher than the other treatments. All treatments met the harmless standards for compost. The seed germination index (GI) was largest under O21 and 15.1% higher than that under CK, and the non-toxic compost degree was higher. Redundancy analysis showed that the temperature, C/N, pH, and GI were important factors that affected the microbial community composition. The temperature, C/N, and pH were significantly positively correlated with Firmicutes and Actinobacteria (p < 0.05). Firmicutes was the dominant phylum in the mesophilic stage (2-6 days) and it accounted for a large proportion under O21, where the strong thermophilic metabolism increased the production of heat and prolonged the high temperature period. The bacterial genus Ammoniibacillus in Firmicutes accounted for a large proportion under O21 and it accelerated the decomposition of substrates. Therefore, the addition of MNBW changed the microbial community to affect the maturation of the compost, and the quality of the compost was higher under O21.

Long-term response of the microbial community to the degradation of DOC released from Undaria pinnatifida

With the aim to study the mechanism underlying the macroalgal carbon sequestration driven by microbes, we investigated the microbial community using metagenomics methods and its long-term degradation of dissolved organic carbon (DOC) derived from Undaria pinnatifida. It was observed that after removing U. pinnatifida, the concentration of the DOC decreased significantly (p < 0.05) within 4 days. Over a period of 120 days of degradation, the concentration of remaining DOC (26%) remained stable. The succession of microbial community corresponded to the three stages of DOC concentration variation. Moreover, the structure of microbes community and its metabolic function exhibited evident patterns of succession. The concentration of DOC was correlated negatively with the abundances of Planctomycetaceae (p < 0.01), and was correlated positively with the abundances of Roseobacteraceae and Rhodobacteraceae (p < 0.01). In addition, the metabolic pathways related to "Glycolysis/Gluconeogenesis", "Alanine, aspartate, and glutamate metabolism", "Citrate cycle (TCA cycle)" and "Tryptophan metabolism" was significantly correlated with the variations in DOC concentration (p < 0.05). These findings indicate that the variation in the DOC concentration was closely linked to the succession of Planctomycetaceae, Roseobacteraceae, Rhodobacteraceae, and the degradation of DOC derived from U. pinnatifida appeared to be influenced by metabolic functions.

Metagenomics reveals the microbial community and functional metabolism variation in the partial nitritation-anammox process: From collapse to recovery

Mainstream partial nitritation-anammox (PNA) process easily suffers from performance instability and even reactor collapse in application. Thus, it is of great significance to unveil the characteristic of performance recovery, understand the intrinsic mechanism and then propose operational strategy. In this study, we combined long-term reactor operation, batch tests, and metagenomics to reveal the succession of microbial community and functional metabolism variation from system collapse to recovery. Proper aeration control (0.10-0.25 mg O2/L) was critical for performance recovery. It was also found that Candidatus Brocadia became the dominant flora and its abundance increased from 3.5% to 11.0%. Significant enhancements in carbon metabolism and phospholipid biosynthesis were observed during system recovery, and the genes abundance related to signal transduction was dramatically increased. The up-regulation of sdh and suc genes showed the processes of succinate dehydrogenation and succinyl-CoA synthesis might stimulate the production of amino acids and the synthesis of proteins, thereby possibly improving the activity and abundance of AnAOB, which was conducive to the performance recovery. Moreover, the increase in abundance of hzs and hdh genes suggested the enhancement of the anammox process. Changes in the abundance of key genes involved in nitrogen metabolism indicated that nitrogen removal pathway was more diverse after system recovery. The achievement of performance recovery was driven by anammox, nitrification and denitrification coupled with dissimilatory nitrate reduction to ammonium. These results provide deeper insights into the recovery mechanism of PNA system and also provide a potential regulation strategy for the stable operation of the mainstream PNA process.

Deciphering the internal driving mechanism of microbial community for carbon conversion and nitrogen fixation during food waste composting with multifunctional microbial inoculation

In this study, the effects of multifunctional microbial inoculation on food waste composting based on the synergistic property between organic matter degradation and nitrogen fixation were investigated. The results showed that inoculation simultaneously strengthened organic matter degradation by 9.9% and improved the nitrogen content by 20.6% compared with that of the control group. Additionally, spectral analysis demonstrated that inoculation was conducive to the enhanced humification, which was supported by the improvement in polyphenol oxidase activity. Microbial analysis showed that most of the introduced microorganisms (Bacillus, Streptomyces, Saccharomonospora) successfully colonized, and stimulated the growth of other indigenous microorganisms (Enterobacter, Paenibacillus). Meanwhile, the change in microbial community structure was accompanied by the enhanced tricarboxylic acid cycle and amino acid metabolism. Furthermore, network analysis and structural equation model revealed that the enhanced cooperation of microorganisms, in which more carbon sources could be provided by cellulose decomposition for nitrogen fixation.

Effects of Bacillus subtilis on carbon components and microbial functional metabolism during cow manure-straw composting

This study is the first to investigate the changes in the composting process and carbon conversion in a cow manure-straw compost matrix with Bacillus subtilis added at four different levels (0, 0.5%, 1%, and 2% w/w compost), and to explain the mechanism responsible for carbon conversion through microbial functional metabolism. Inoculation with Bacillus subtilis at 2% had the best effect on fermentation among all treatments, but it inhibited the synthesis of total organic carbon and humus. Bacillus subtilis at 0.5% reduced mineralization in the cooling and maturity stages of composting, and enhanced the humification of carbon. The total organic carbon and humic sequence contents were significantly higher with Bacillus subtilis at 0.5% (12.5% and 20.2%, respectively) than Bacillus subtilis at 2% (P < 0.05). Redundancy analysis demonstrated that the pH and microbial functional metabolism were closely related to carbon sequestration during composting.

Composition and functional diversity of microbial community across a mangrove-inhabited mudflat as revealed by 16S rDNA gene sequences

The gradient distribution of microbial communities has been detected in profiles along many natural environments. In a mangrove seedlings inhabited mudflat, the microbes drive a variety of biogeochemical processes and are associated with a dramatically changed environment across the tidal zones of mudflat. A better understanding of microbial composition, diversity and associated functional profiles in relation to physicochemical influences could provide more insights into the ecological functions of microbes in a coastal mangrove ecosystem. In this study, the variation of microbial community along successive tidal flats inhabited by mangrove seedlings were characterized based on the 16S rDNA gene sequences, and then the factors that shape the bacterial and archaeal communities were determined. Results showed that the tidal cycles strongly influence the distribution of bacterial and archaeal communities. Dissimilarity and gradient distribution of microbial communities were found among high tidal flat, mid-low tidal flat and seawater. Discrepancies were also as well observed from the surface to subsurface layers specifically in the high tidal flat. For example, Alphaproteobacteria displayed an increasing trend from low tidal to high tidal flat and vice versa for Deltaproteobacteria; Cyanobacteria and Thaumarchaeota were more dominant in the surface layer than the subsurface. In addition, by classifying the microorganisms into metabolic functional groups, we were able to identify the biogeochemical pathway that was dominant in each zone. The (oxygenic) photoautotrophy and nitrate reduction were enhanced in the mangrove inhabited mid tidal flat. It revealed the ability of xenobiotic metabolism microbes to degrade, transform, or accumulate environmental hydrocarbon pollutants in seawater, increasing sulfur-related respiration from high tidal to low tidal flat. An opposite distribution was found for major nitrogen cycling processes. The shift of both composition and function of microbial communities were significantly related to light, oxygen availability and total dissolved nitrogen instead of sediment types or salinity.