Alginate Gene Regulation

Use of an algD promoter-driven expression system for the degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by Pseudomonas sp. HK-6

Pseudomonas sp. HK-6 is able to utilize hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) as a sole nitrogen source. The HK-6 strain was stimulated to produce an exopolymer, mainly alginate, as a stress response when grown in LB broth containing RDX, synthesizing ~230 μg/mL after 48 h. The algA mRNA levels in HK-6 increased by 7-8-fold after 2-6 h of exposure to 0.1 mM RDX, as measured by RT-qPCR. HK-6 was able to degrade ~25 % of 0.1 mM RDX after 20 days and 60 % after 50 days, whereas the pnrB null mutant only degraded less than 1 % after 50 days. The introduction of an algD promoter-pnrB gene fusion into the pnrB mutant fully restored RDX-degradation capability. To facilitate a study of PnrB action on RDX, a His6-PnrB fusion protein was heterologously expressed in E. coli BL21 cells, and the enzymatic activity on RDX was assayed by measuring the decrease in absorbance at 340 nm due to NADH oxidation. At the fixed condition of 0.1 mM RDX, 0.2 mM NADH, and 1 μg His6-PnrB, the absorbance at 340 nM gradually decreased and reached to its minimum value after 30 min. However, calculating the V max and K m values of PnrB for RDX was challenging due to extremely low solubility of RDX in water. The results clearly indicate the potential use of the algD promoter in studies of some genes in Pseudomonas species.

A dynamic and intricate regulatory network determines Pseudomonas aeruginosa virulence

Pseudomonas aeruginosa is a metabolically versatile bacterium that is found in a wide range of biotic and abiotic habitats. It is a major human opportunistic pathogen causing numerous acute and chronic infections. The critical traits contributing to the pathogenic potential of P. aeruginosa are the production of a myriad of virulence factors, formation of biofilms and antibiotic resistance. Expression of these traits is under stringent regulation, and it responds to largely unidentified environmental signals. This review is focused on providing a global picture of virulence gene regulation in P. aeruginosa. In addition to key regulatory pathways that control the transition from acute to chronic infection phenotypes, some regulators have been identified that modulate multiple virulence mechanisms. Despite of a propensity for chaotic behaviour, no chaotic motifs were readily observed in the P. aeruginosa virulence regulatory network. Having a ‘birds-eye’ view of the regulatory cascades provides the forum opportunities to pose questions, formulate hypotheses and evaluate theories in elucidating P. aeruginosa pathogenesis. Understanding the mechanisms involved in making P. aeruginosa a successful pathogen is essential in helping devise control strategies.