Abstract
The Gram-positive model organism Bacillus subtilis produces the essential second messenger signaling nucleotide cyclic di-AMP. In B. subtilis and other bacteria, c-di-AMP has been implicated in diverse functions such as control of metabolism, cell division and cell wall synthesis, and potassium transport. To enhance our understanding of the multiple functions of this second messenger, we have studied the consequences of c-di-AMP accumulation at a global level by a transcriptome analysis. C-di-AMP accumulation affected the expression of about 700 genes, among them the two major operons required for biofilm formation. The expression of both operons was severely reduced both in the laboratory and a non-domesticated strain upon accumulation of c-di-AMP. In excellent agreement, the corresponding strain was unable to form complex colonies. In B. subtilis, the transcription factor SinR controls the expression of biofilm genes by binding to their promoter regions resulting in transcription repression. Inactivation of the sinR gene restored biofilm formation even at high intracellular c-di-AMP concentrations suggesting that the second messenger acts upstream of SinR in the signal transduction pathway. As c-di-AMP accumulation did not affect the intracellular levels of SinR, we conclude that the nucleotide affects the activity of SinR.
Highlights
Many bacteria are able to choose between a variety of different lifestyles
Our results indicate that accumulation of c-di-AMP inhibits biofilm formation, and that this second messenger seems to affect the activity of the SinR transcription factor
To study the impact of cyclic di-AMP on the physiology of B. subtilis at a global level, we compared the transcriptomes of wild type strain 168 and strain GP2040 lacking both c-di-AMP specific phosphodiesterases (GdpP and PgpH)
Summary
Many bacteria are able to choose between a variety of different lifestyles. Depending on the growth state, the Gram-positive soil bacterium Bacillus subtilis has a large repertoire of potential choices. In B. subtilis, biofilm formation and motility are two mutually exclusive lifestyles, and the choice between them is regulated at the levels of protein activities and gene expression c-di-AMP Controls Biofilm Formation in Bacillus subtilis (Vlamakis et al, 2013). Regulation at the level of gene expression is achieved by the master regulator SinR that binds to the promoter regions of two major operons required for biofilm formation, the tapA-sipW-tasA operon and the 15 gene epsA-O operon (Chu et al, 2006) The former operon encodes the amyloid-like fiber protein TasA and the proteins required for its export and assembly (Romero et al, 2014). Our results indicate that accumulation of c-di-AMP inhibits biofilm formation, and that this second messenger seems to affect the activity of the SinR transcription factor
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