Exopolymer Biosynthesis and Proteomic Changes of Pseudomonas sp. HK-6 Under Stress of TNT (2,4,6-Trinitrotoluene)

Scanning electron microscopy revealed pores and wrinkles on the surface of Pseudomonas sp. HK-6 cells grown in Luria Bertani (LB) medium containing 0.5 mM TNT (2,4,6-trinitrotoluene). Exopolymer connections were also observed on the wild-type HK-6 cells but not on the algA mutant cells. In addition, the amount of exopolymer from HK strain increased from 90 to 210 microg/mL under TNT stress, whereas the algA mutant produced approximately 30 microg/mL, and its exopolymer production was little increased by TNT stress. These results indicate that TNT stress induced exopolymer production with alginate as a major component. The algA mutant degraded TNT more slowly than the wild-type HK-6 strain. HK-6 was able to completely degrade 0.5 mM TNT within 8 days, whereas algA mutant only achieved approximately 40% within the same time period. Even after 20 days, no more than 80% of TNT was degraded. According to analyses of proteomes of HK-6 and algA mutant cells grown under TNT stress or no stress, several proteins (KinB, AlgB, Alg8, and AlgL) in alginate biosynthesis were only highly induced by both strains under TNT stress. Interestingly, two stress-shock proteins (SSPs), GroEL and RpoH, were more highly expressed in the algA mutant than the HK-6 strain. The algA mutant was rendered more vulnerable to environmental stress and had reduced ability to metabolize TNT in the absence of alginate synthesis.