RpoS and Stationary Phase Stress Survival in Azotobacter vinelandii
Abstract Text
As a stress survival tactic Azotobacter vinelandii has the ability to form desiccation resistant cysts viable for long periods of time. Strains UWD (algU negative) and 113 (algU positive) over-produce poly-hydroxybutyrate (PHB), alginate and alkyl-resorcinol. The stationary phase sigma factor, RpoS appears to play a role in the production of all three of these molecules in both UWD and 113. Through the insertion of a kanamycin cassette, rpoS mutants of strains UWD and 113 were constructed using homologous recombination. In these mutants, UWDS and 113S respectively, the production of PHB and alginate was significantly delayed and never reached the same levels as the wild type strains. Both mutant strains showed no signs of alkyl-resorcinol production. In addition to playing a role in stationary phase survival, RpoS also plays a role in stress survival in many organisms including Escherichia coli and Pseudomonas aeruginosa. We suspect this is the also the case with A. vinelandii in its formation of cysts during stationary phase. At this time there are no enzymes or genes known to be associated with encystment, other than the knowledge that alginate and alkyl resorcinol are important products required for this process. Using two-dimensional proteomics we have been able to show several differences in protein profiles between wild type cells and rpoS mutant cells indicating that RpoS regulates the expression of several genes in A. vinelandii. One of these genes has been identified as a putitive uridylate kinase using mass spectrometry. Work that is currently in progress aims to identify more genes regulated by RpoS that play a role in encystment.
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