Effects of interspecific interactions on biofilm formation potential and chlorine resistance: Evaluation of dual-species biofilm observed in drinking water distribution systems

Interspecific interactions could influence microbial resistance to disinfectants in drinking water distribution systems (DWDS). Understanding the effects of interspecific interactions on biofilm formation potential and chlorine resistance could improve future disinfection strategies and prevent the spread of infectious water-borne diseases. The present study first investigated biofilm formation of 10 bacterial groups with two mixed bacterial strains isolated from a simulated DWDS over different incubation times (24 h, 48 h, and 72 h), and then evaluated chlorine resistance of the 72 h incubated biofilms under residual 0.3, 0.6, 1, 2, 4, and 10-mg/L chlorine concentrations. The Acidovorax + Acinetobacter, Sphingomonas + Bacillus, Sphingomonas + Acidovorax, and Acidovorax + Microbacterium groups exhibited high biofilm formation potential, which could be attributed to synergism interactions. The Acinetobacter + Microbacterium, Sphingomonas + Microbacterium, and Sphingomonas + Acinetobacter groups exhibited weak or moderate biofilm formation potential, which could be attributed to competition interactions. The Acidovorax + Bacillus, Bacillus + Acinetobacter, and Bacillus + Microbacterium groups exhibited moderate biofilm formation potential, which could be attributed to the neutralism interactions. The chlorine resistance of most of the dual-species biofilms associated with Sphingomonas sp. and Bacillus cereus was higher than those of the corresponding single-species biofilms. Considering the interspecific interactions between the Microbacterium laevaniforms and four other species were mainly either neutralism or competition interactions, the chlorine resistance of the group associated with M. laevaniforms could be inhibited to some extent. The specific structures (e.g., extracellular polymeric substances and spores) of dual-species biofilm had a greater influence on chlorine resistance than interspecific interactions. There were diverse interspecific interactions. Synergism could promote chlorine resistance in dual-species biofilm, neutralism had minimal effect on the chlorine resistance, while competition could reduce the chlorine resistance, and the reduction in chlorine resistance could be mitigated if there were specific morphological structures in the biofilm such as spores.