Biofilm formation and heavy metal resistance by an environmental Pseudomonas sp.

We have isolated a heavy metal resistance Pseudomonas sp. (designated as strain EJ01) and demonstrated that this bacterium was able to tolerate cadmium ion (Cd2+) in the growth medium up to 7 mM. At stationary phase, cells of strain EJ01 aggregated and formed biofilm when concentrations of Cd was high (2 mM and above). This phenomenon might be related to the bacterium's ability to produce exopolysaccharides (EPS). Strain EJ01 also showed resistance to other toxic heavy metals examined. Concentrations of heavy metal was reduced significantly when Pseudomonas sp. EJ01 grown in the medium containing these toxic metal ions. Biofilm formation and EPS production were important for the bacterium's resistance against heavy metals. Exopolysaccharide was produced by strain EJ01 and 50% more EPS was produced when the cells grown in the medium containing 2 mM CdCl2 compared to those grown on the medium without heavy metals. A biofilm defective mutant (strain m-3055) was obtained by transposon mutagenesis. Although strain m-3055 produced comparable amount of EPS to that of strain EJ01, the mutant showed less tolerance to the toxic heavy metals. Heavy metal removal from the culture medium by strain m-3055 was also significantly reduced compared to strain EJ01.

► Pseudomonas sp. strain EJ01 can resist high concentration of heavy metals.
► Biofilm formation and exopolysaccharide are important for the heavy metal resistance.
► Biofilm mutant (strain m-3055) was generated by transposon mutagenesis.
► Strain m-3055 was less tolerance to heavy metals compared to strain EJ01.
► Metal removal from medium was significant in strain EJ01 but not in strain m-3055.