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|Title:||Late stationary phase-specific gene expression in Escherichia coli|
Morton, Richard A.
|Abstract:||Interest in stationary phase and adaptation mechanisms to non-optimal conditions led to the discovery of RpoS as a growth phase-dependent sigma factor. Subsequently, studies aimed at profiling members of the RpoS regulon have provided insights into the stationary phase of growth. At the same time, stationary phase physiology, which now includes formation of biofilms and persistence, is characterized by many RpoS-independent but growth phase-dependent genes, which have received less attention. Obtaining a comprehensive understanding of stationary phase requires a comprehensive profiling of these genes. We employed a plasmid-based promoter gfp::mut2 fusion library of 1920 promoters to screen for promoters active in planktonic culture during long-term incubation. Two hundred and twenty nine identified promoters fall into molecular function categories of catalytic activity, transport, stress-response, replication inhibition, and transcription. Only 35 of these are positively-regulated by RpoS and 15 are negatively-dependent during early stationary phase. We found that levels of rpoS transcript peak during fast growth conditions of early stationary phase (OD600 = 1.5) and decrease thereafter. Induction of tryptophanase, which produces indole, was discovered to be RpoS-independent but stationary phase-specific at the transcript and protein levels. Furthermore, RpoS serves to limit TnaA levels following initial induction in a dose dependent manner. At the transcript level, RpoS positively regulates TnaA in exponential phase (OD600 = 0.3) but negatively in early stationary phase (OD600 = 1.5). The mechanism underlying this switch is unknown. Thus, mature stationary phase cultures are characterized by a physiology that is at least partially, if not completely, distinct from early stationary phase cells and RpoS-independent but stationary phase-specific genes play an important role during prolonged starvation.|
|Appears in Collections:||Open Access Dissertations and Theses|
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