Effect of rpoS inactivation on biofilm formation of a p-nitrophenol degrading Pseudomonas putida strain

Abstract

With the widespread existence of environmental pollutants in the modern world, effective, non-destructive means of remediation are becoming more and more desirable as an alternative to the traditional excavation and incineration. Bioremediation, the use of pollutant degrading biological processes to cleanse an area, is a highly viable and realistic option. In a polluted area, organisms must be able to withstand a considerable amount of environmental stresses. Both biofiims and the stationary-phase sigma factor, RpoS, have been shown to aid in bacterial survival and thus their relationship to each other may provide clues to increasing the survival of remediating organisms. The effect of rpoS deletion on the biofilm forming ability of a p-nitrophenol degrading Pseudomonas putida strain was examined. When examined in a simple Crystal Violet assay the rpoA'-knockout mutant showed a greater amount of cells attached to the glass test tubes than did the wild-type. This observation was mirrored by confocal microscopy images which showed a greater amount of growth, quicker growth, and a greater degree of mature biofilm structure for the knockout cultures versus the wild-type. Converted to quantitative results, all parameters of biovolume, percent substrate coverage, thickness and roughness showed a significantly greater difference between the knockout and the wild-type P. putida. There were no significant differences in hydrophobicity values for the two cultures and it is unlikely that hydrophobicity played a role in the observed biofilm differences. Taken together, these results indicate a close relationship between RpoS and biofilm formation in P. putida, and are promising for future bioremediation studies.