1887

Abstract

The response regulator CtrA controls the expression of 227 genes, some of which are upregulated by both the phosphorylated and unphosphorylated forms of CtrA. Therefore, CtrA concentration alone, regardless of phosphorylation state, may determine expression of downstream genes, yet little is known about the regulation of in . In this study we used a  : :  fusion plasmid to study the effects of medium composition, growth conditions and growth phase on gene expression. These experiments indicate that expression is higher when cultures are grown in phototrophic (anaerobic) conditions compared with chemotrophic (aerobic) conditions, and is higher when grown in a minimal medium compared with a rich medium. We used several mutants to investigate possible regulatory pathways, and found that in is not autoregulated but is regulated by a quorum-sensing system. The expression of increased as cell cultures moved through exponential phase and into stationary phase, with high levels of expression persisting long after culture turbidity plateaued. Although this growth phase-dependent pattern of expression was also observed in a quorum-sensing mutant, the magnitude of expression was about 50 % of the wild-type strain at all phases. Furthermore, reduction of phosphate concentration in the growth medium decreased expression in a culture density-independent manner, whereas reduction of malic acid (carbon source) or ammonium (nitrogen source) concentration had no effect. The regulation of expression in appears to require the coordination of multiple pathways involved in detecting a variety of environmental conditions.

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2013-01-01
2020-01-27
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