Second Messenger Signaling in Bacillus subtilis: Accumulation of Cyclic di-AMP Inhibits Biofilm Formation

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.

Cyclic di-GMP: second messenger extraordinaire

“…C-di-AMP is associated with a growing list of cellular functions primarily in gram-positive bacteria. These include cell wall homeostasis 115,[117][118][119][120] , DNA integrity 2,121-123 , potassium homeostasis 104,[124][125][126] and osmoprotection 127,128 , gene expression 129,130 , biofilm formation 131,132 , sporulation 133 , metabolism 102 , resistance to antibiotics 134 , and, similar to c-di-GMP, cell-mediated adaptive immune response (see below). c-GMP-AMP is of special interest because it is produced by bacteria and metazoans 3,135 .…”

Structural and functional studies of pyruvate carboxylase regulation by cyclic di-AMP in lactic acid bacteria

“…aspartate biosynthesis | pyruvate carboxylase | cyclic di-AMP B acteria use various signaling molecules to regulate their complex physiology. Cyclic di-3′,5′-adenosine monophosphate (c-di-AMP) has emerged as a broadly conserved bacterial second messenger that has been implicated in a wide range of cellular processes, including cell wall homeostasis (1)(2)(3), biofilm formation (4,5), central metabolism (6), osmoregulation (7,8), and potassium transport (9). In various pathogenic bacteria, c-di-AMP is essential for mediating host-pathogen interactions and promoting virulence (1,(10)(11)(12)(13).…”

“…Moreover, the compound itself can adopt diverse conformations to fit into the unique binding pocket present in each target. In some structures, c-di-AMP binds symmetrically to a dimeric protein (6,7,16,17), while in others c-di-AMP binds in an asymmetric fashion, with each adenine being recognized differently (5,15,18,20,21). In many structures, c-di-AMP adopts a U-shaped structure, with the two adenine bases forming the walls of the U, while in others, it is found in a more extended configuration.…”

Cyclic‐di‐GMP signalling meets extracellular polysaccharide synthesis in Bacillus subtilis

“…Consistent with the c-di-GMP independent biofilm formation in B. subtilis, this enzyme does not have a counterpart in B. subtilis. Interestingly, another second messenger has been implicated in the control of biofilm formation in B. subtilis: accumulation of the essential second messenger cyclic di-AMP results in strongly reduced expression of the genes required for matrix production and, thus, to the inability of the bacteria to form biofilms (Gundlach et al, 2016). C-di-AMP is thought to be involved in cell wall homeostasis and the control of potassium uptake (Commichau et al, 2015), and the molecular mechanisms by which c-di-AMP interferes with biofilm formation are poorly understood.…”