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

The Escherichia coli morphogene bolA causes round morphology when overexpre ssed. The expression of bolA is mainly regulated by a sigma(S)-dependent ge arbox promoter bolA1p. Such regulation results in increased relative levels of expression at slow growth rates, as seen with those attained at the ons et of stationary phase. We demonstrate that bolA1p is also induced during e arly logarithmic growth in response to several forms of stress, and that th is induction can be partially sigma(S) independent. Sudden carbon starvatio n results in a 17-fold increase in mRNA levels derived from bolA1p Ih after stress imposition. Increased osmolarity results in a more than 20-fold inc rease after the same period. Considerable increases in bolA1p mRNA levels w ere also detected as a result of heat shock, acidic stress and oxidative st ress, which has been shown to inhibit sigma(S) translation. The orders of m agnitude 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 statio nary phase. Increased expression and morphological changes due to sudden ca rbon starvation and osmotic shock still occur when sigma(S) is not present in a rpoS(-) background. The results show that expression of bolA is not co nfined to stationary phase, but it can also play an important role in gener al stress response. We propose that bolA1p stress induction overrides the n ormal regulation imposed by growth rate, which is strictly the result of si gma(S)-directed transcription.