Ecological response mechanism of alkaline wastewater periphytic biofilms to pH alteration

The environmental impact of indiscriminate alkaline wastewater discharge is increasingly concerning. Studying the ecological response mechanisms of periphytic biofilms to such wastewater is crucial for deepening our understanding of its broader environmental implications. In this study, periphytic biofilms collected from the drainage outlet of a tunnel construction project were developed for 56 days at initial pH values of 10 (pH0 10) and 12 (pH0 12). These stabilized biofilms were then transferred to a neutral environment (pH 7) for another 35 days. High-throughput 16S rRNA sequencing revealed changes in the growth characteristics, microbial interactions, and microbial community composition, function, and assembly patterns of the biofilms. Specifically, results revealed decreased microbial activity, live/dead bacteria ratios, and polysaccharide content in extracellular polymeric substances when the pH was reduced from alkaline to neutral, with incomplete recovery observed after 35 days of incubation in a neutral environment. During neutral pH incubation, proteobacterial abundance increased by 58.39 % and 33.08 % in biofilms cultured at pH0 10 and pH0 12, respectively, becoming the dominant flora, with chemoheterotrophic functions increasing by 8.11 % and 38.23 %, respectively. Network analysis indicated that biofilms in the pH0 12 culture group had a more advanced organizational co-occurrence network, with more complex and stable interactions, than those in the pH0 10 culture group. Microbial community α diversity, key differential species count, the proportion of positively correlated network edges, and null model data showed that microbial communities in biofilms cultured at pH0 10 were more resilient, whereas those cultured at pH0 12 were more resistant. Overall, this study reveals that alkaline wastewater periphytic biofilms adapt and develop high tolerance and metabolic activity but struggle to recover their original state in a short-term neutral environment, with biofilms cultured at pH0 12 exhibiting more complex interactions and higher resistance and those cultured at pH0 10 showing greater resilience. [Display omitted] •pH affects biofilm growth, structure, and microbial interactions and communities.•Proteobacteria adapt quickly to pH changes and maintain biofilm function.•Biofilms with higher initial pH have more complex and stable co-occurrence networks.•Competitive exclusion and preferential effects help biofilms tackle pH changes.•Biofilms cu