Casing soil is a key step in the production of Oudemansiella raphanipes. Bacterial community in casing soil plays key roles in the growth and development of edible fungi. However, a knowledge gap remains regarding the bacterial community shifts in casing soil before and after the cultivation of O. raphanipes (CSBACO). Casing soil samples before and after the cultivation of O. raphanipes (CSBC and CSAC) were collected and examined by high-throughput 16S rRNA gene sequencing technology. Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were dominant phyla in casing soil of O. raphanipes, which accounted for 77.32% of the total abundance. After the cultivation of O. raphanipes, the alpha diversity of bacterial community and the relative abundance of some beneficial genera such as Marmoricola, Nocardioides, Sphingomonas, and Streptomyces decreased, while that of bacteria belonging to the candidate class MB-A2-108 tolerant to adverse environment significantly increased. Meanwhile, physicochemical properties of casing soil changed significantly in CSBACO. Soil ammonium nitrogen and organic matter greatly decreased in CSAC and they mainly influenced bacterial community before the cultivation of O. raphanipes. In contrast, available potassium and pH significantly increased in CSAC and mainly affected bacterial community after the cultivation of O. raphanipes. Furthermore, the relative abundance of bacteria with the function of amino acid and lipid metabolism decreased, while that of bacteria functions related to parasites and pathogens increased, which further revealed the significance of bacterial community in casing soil. Diversity, composition, and the potential function of bacterial community shifted dramatically in CSBACO. The results deepen the understanding of the bacterial community and its microecological mechanism in casing soil of O. raphanipes.

It is well accepted that the high performance of wastewater treatment plants (WWTPs) relies on the microbial community in activated sludge (AS). Hence, it is crucial to illuminate the geographic distributions and influencing factors of the ecological strategies employed by the AS microbial community. Here, we investigated how the ecological strategies of AS microbial communities influenced their ecological characteristics in 60 WWTPs across 15 cities in China. Our study showed that the average rrn copy number of the whole AS microbial community across China was 2.25 ± 0.12. The highest average rrn copy number of the core community indicated that core members tend to be r-strategists with an advantage in rapid pollutant removal and recovery of the community after environmental disturbances. High nutrient availability promoted microorganisms with higher average rrn copy numbers, while long sludge retention time (SRT) was preferred to the microorganisms with lower average rrn copy numbers. Homogenous selection and dispersal limitation were the predominant assembling processes at the city level, with a shift from deterministic to stochastic processes with increasing average rrn copy numbers. Furthermore, more r-strategists participated in chemoheterotrophic functions, while more K-strategists were related to the nitrification processes. Overall, our findings enrich the knowledge of AS microbial ecology and lay the theoretical foundation for the precise regulation of WWTPs.

Temperature is a major abiotic factor shaping activated sludge microbiomes and pollutant removal, yet how it regulates microbial carbon and nitrogen metabolic pathways remains poorly understood. Herein, a lab-scale SBR was run at 10, 20 and 30 ℃ corresponding to seasonal aeration tank temperatures of domestic municipal WWTPs. Metagenomic and 16S rRNA gene sequencing were employed to unravel microbial mechanisms governing carbon and nitrogen removal. COD removal consistently exceeded 90% regardless of temperature changes and no significant differences were identified in the abundance of carbon-cycling functional genes or dominant metagenome-assembled genomes (MAGs) among treatments. Nitrogen removal, however, was severely inhibited at 10 °C with substantial nitrite accumulation. At 10 °C, microbial community showed the highest proportion of deterministic assembly (28.84%), a low AVD value (0.81 ± 0.01) and the minimal abundance-weighted rrn operon copy number (1.77 ± 0.04), collectively indicating the highest community stability. However, MAGs carrying amoC and napA were depleted and only terminal denitrification genes (nosZ and norB) were enriched. At 20 °C, the microbial community displayed intermediate community stability and moderate nitrogen removal efficiency. The microbial community at 30 °C was relatively unstable, as evidenced by the lowest community richness (847.67 ± 23.44), the highest AVD, and an elevated average rrn operon copy number. But the ammonia assimilation genes (gdhA, glnA), nitrite reduction gene (nrfH), assimilatory nitrate reduction gene (nasB), and assimilatory nitrite reduction gene (nirD) were co-enriched. Overall, carbon metabolism gains temperature resistance via functional redundancy, while nitrogen removal presents a stability-efficiency trade-off under thermal stress.