Mutability and survival of pseudomonas aeruginosa in multi-species drinking water biofilm communities

Abstract

Pseudomonas aeruginosa is an important opportunistic pathogen of humans and also has the ability to form biofilms in drinking water. However, the survival, persistence and the control of this pathogen within mixed-species bacterial communities in drinking water distribution systems remains poorly understood.

Strains of P. aeruginosa obtained from natural and pathogenic biofilms are often hypermutable due to defective DNA error repair systems. However, the role of mutation in determining survival and fitness of P. aeruginosa within the environment has not been explored. This work, investigated the mutability, persistence and survival of hypermutable mutS, wild type and environmental strains of P. aeruginosa within mixed species drinking water consortia and the effects of oxidative stress and water treatment practices including chlorination and UV irradiation on their mutability and persistence within these biofilms using a flow cell continuous culture system. Our results show that P. aeruginosa hypermutator strains integrated and persisted within the biofilm more readily than the wild type and environmental strains. Moreover, growth of P. aeruginosa within a multi-species biofilm led to a 5-fold increase in the mutation frequency (resistance to rifampicin, RifR) of the wild type strain compared to monospecies P. aeruginosa biofilms, suggesting that interactions within polymicrobial communities may promote genetic diversification. Our results also show that antioxidants (L-proline and N-acetyl-cysteine) had an average of 4-fold reduction effect in the mutation frequency of the wild type P. aeruginosa within the mixed species biofilms. However, the mutation frequency exhibited by the mutS strain within the biofilms is independent of oxidative stress. UV irradiation of P. aeruginosa cells, but not exposure to chlorine, led to increases in P. aeruginosa RifR mutation frequency and enhanced the persistence of surviving P. aeruginosa cells within drinking water biofilms. These findings therefore have provided new insights into mechanisms by which drinking water biofilms may harbour important pathogenic micro-organisms and how these interactions within the multispecies biofilms can enhance genetic adaptation and evolution of microbial pathogens.

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ORCID for Jeremy Webb: orcid.org/0000-0003-2068-8589

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