Physiological and genetic evidence for an OmpB signal transduction system in Erwinia chrysanthemi

Master Thesis


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University of Cape Town

In order for bacteria to survive in their environment they must continuely sense signals such as, presence of host organisms, chemical concentrations, or variationsin other physiological parameters. Many bacteria sense their environment through the use of a two component regulatory systems. These systems usually employ the use of two different proteins, a sensor protein and its cognate response regulator. Some bacteria can survive fluctuations in medium osmolarity through the use of a two component signal transduction system. In Escherichia coli and Salmonella typhimurium this two component system includes the EnvZ sensor protein and its cognate response regulator, OmpR. The two genes that code for these proteins are envZ and ompR genes respectively. The two genes together form the ompB operonrespectively. This operon regulates the expression of two outer membrane proteins, OmpF and OmpC in response to medium osmolarity in E. coli.Erwinia chrysanthemi has been found to be sensitive to desication. Proliferation of soft rot, caused by this organism, has also been associated with irrigation. E.chrysanthemi has also been observed to respond to changes in medium osmolarity. Evidence of an ompB operon was thus sought. Outer membrane proteins were isolated using sodium lauroylsarcosine. Three major outer membrane proteins were isolated, namely Ompl (37.5 kd), Omp2 (35.5 kd) and Omp3 (34.5 kd). Increase in medium osmolarity resulted in an increase in expression of Omp3, while Ompl was suppressed. This lends support to the presence of an ompB like signal transduction system in E. chrysanthemi. Growth temperature was shown to have no effect on the expression of the major OMP. Similarly, culture growth phase had no effect on major OMP expression. However, two induced OMP were present from mid log phase onwards.

Bibliography: pages 132-155.