Commensal Interactions in a Dual-Species Biofilm Exposed to Mixed Organic Compounds

Abstract

ABSTRACT There is limited knowledge of interspecies interactions in biofilm communities. In this study, Pseudomonas sp. strain GJ1, a 2-chloroethanol (2-CE)-degrading organism, and Pseudomonas putida DMP1, a p -cresol-degrading organism, produced distinct biofilms in response to model mixed waste streams composed of 2-CE and various p -cresol concentrations. The two organisms maintained a commensal relationship, with DMP1 mitigating the inhibitory effects of p -cresol on GJ1. A triple-labeling technique compatible with confocal microscopy was used to investigate the influence of toxicant concentrations on biofilm morphology, species distribution, and exopolysaccharide production. Single-species biofilms of GJ1 shifted from loosely associated cell clusters connected by exopolysaccharide to densely packed structures as the p -cresol concentrations increased, and biofilm formation was severely inhibited at high p -cresol concentrations. In contrast, GJ1 was abundant when associated with DMP1 in a dual-species biofilm at all p -cresol concentrations, although at high p -cresol concentrations it was present only in regions of the biofilm where it was surrounded by DMP1. Evidence in support of a commensal relationship between DMP1 and GJ1 was obtained by comparing GJ1-DMP1 biofilms with dual-species biofilms containing GJ1 and Escherichia coli ATCC 33456, an adhesive strain that does not mineralize p -cresol. Additionally, the data indicated that only tower-like cell structures in the GJ1-DMP1 biofilm produced exopolysaccharide, in contrast to the uniform distribution of EPS in the single-species GJ1 biofilm.