Assessing the response of degradative biofilms to groundwater pollutants
There is limited knowledge of interspecies interactions in biofilm communities. In this study, Pseudomonas sp. GJ1, a 2-chloroethanol (2-CE) degrading organism, and Pseudomonas putida DMP1, a p-cresol degrader, produced distinct biofilms in response to model mixed waste streams comprised 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 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 only present 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 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.