The stationary‐phase morphogene bolA from Escherichia coli is induced by stress during early stages of growth

JM Santos, P Freire, M Vicente… - Molecular …, 1999 - Wiley Online Library
JM Santos, P Freire, M Vicente, CM Arraiano
Molecular microbiology, 1999Wiley Online Library
The Escherichia coli morphogene bolA causes round morphology when overexpressed. The
expression of bolA is mainly regulated by a σs‐dependent gearbox promoter bolA1p. Such
regulation results in increased relative levels of expression at slow growth rates, as seen
with those attained at the onset of stationary phase. We demonstrate that bolA1p is also
induced during early logarithmic growth in response to several forms of stress, and that this
induction can be partially σs independent. Sudden carbon starvation results in a 17‐fold …
The Escherichia coli morphogene bolA causes round morphology when overexpressed. The expression of bolA is mainly regulated by a σs‐dependent gearbox promoter bolA1p. Such regulation results in increased relative levels of expression at slow growth rates, as seen with those attained at the onset of stationary phase. We demonstrate that bolA1p is also induced during early logarithmic growth in response to several forms of stress, and that this induction can be partially σs independent. Sudden carbon starvation results in a 17‐fold increase in mRNA levels derived from bolA1p 1 h after stress imposition. Increased osmolarity results in a more than 20‐fold increase after the same period. Considerable increases in bolA1p mRNA levels were also detected as a result of heat shock, acidic stress and oxidative stress, which has been shown to inhibit σs translation. The orders of magnitude of bolA1p induction in log phase due to sudden starvation, osmotic shock and oxidative stress surpass the levels reached in stationary phase. Under sudden carbon starvation and osmotic shock, the cells changed their morphology, resembling those cells in which bolA is overexpressed in stationary phase. Increased expression and morphological changes due to sudden carbon starvation and osmotic shock still occur when σS is not present in a rpoS background. The results show that expression of bolA is not confined to stationary phase, but it can also play an important role in general stress response. We propose that bolA1p stress induction overrides the normal regulation imposed by growth rate, which is strictly the result of σS‐directed transcription.
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