Genomic Distribution of Pro-Virulent cpdB-like Genes in Eubacteria and Comparison of the Enzyme Specificity of CpdB-like Proteins from Salmonella enterica, Escherichia coli and Streptococcus suis

Bacterial second messenger cyclic di-AMP in streptococci

Cyclic dimeric adenosine monophosphate (c-di-AMP) has been well studied in bacteria, including those of the genus Streptococcus, since the first recognition of this dinucleotide in 2008. Streptococci possess a sole diadenylate cyclase, CdaA, and distinct c-di-AMP phosphodiesterases. Interestingly, cdaA is required for viability of some streptococcal species but not all when streptococci are grown in standard laboratory media. Bacteria of this genus also have distinct c-di-AMP effector proteins, diverse c-di-AMP-signaling pathways, and subsequent biological outcomes. In streptococci, c-di-AMP may influence bacterial growth, morphology, biofilm formation, competence program, drug resistance, and bacterial pathogenesis. c-di-AMP secreted by streptococci has also been shown to interact with the mammalian host and induces immune responses including type I interferon production. In this review, we summarize the reported c-di-AMP networks in seven species of the genus Streptococcus, which cause diverse clinical manifestations, and propose future perspectives to investigate the signaling molecule in these streptococcal pathogens.

Insights into the metabolism, signaling, and physiological effects of 2',3'-cyclic nucleotide monophosphates in bacteria

2',3'-cyclic nucleotide monophosphates (2',3'-cNMPs) have been discovered within both prokaryotes and eukaryotes in the past decade and a half, raising questions about their conserved existence in cells. In plants and mammals, wounding has been found to cause increased levels of 2',3'-cNMPs. Roles for 2',3'-cNMPs in plant immunity suggest that their regulation may be valuable for both plant hosts and microbial pathogens. In support of this hypothesis, a plethora of microbial enzymes have been found with activities related to these molecules. Studies in bacteria suggest that 2',3'-cNMPs are also produced in response to cellular stress and modulate expression of numerous genes. 2',3'-cNMP levels affect bacterial phenotypes, including biofilm formation, motility, and growth. Within E. coli and Salmonella enterica, 2',3'-cNMPs are produced by RNA degradation by RNase I, highlighting potential roles for Type 2 RNases producing 2',3'-cNMPs in a range of organisms. Development of cellular tools to modulate 2',3'-cNMP levels in bacteria has allowed for interrogation of the effects of 2',3'-cNMP concentration on bacterial transcriptomes and physiology. Pull-downs of cellular 2',3'-cNMP binding proteins have identified the ribosome and in vitro studies demonstrated that 2',3'-cNMPs decrease translation, suggesting a direct mechanism for 2',3-cNMP-dependent control of bacterial phenotypes. Future studies dissecting the cellular roles of 2',3'-cNMPs will highlight novel signaling pathways within prokaryotes and which can potentially be engineered to control bacterial physiology.

Genomic Distribution of ushA-like Genes in Bacteria: Comparison to cpdB-like Genes

UshA and CpdB are nucleotidases of the periplasm of several Gram-negative bacteria, while several Gram-positives contain cell wall-bound variants. UshA is a 5'-nucleotidase, a UDP-sugar hydrolase, and a CDP-alcohol hydrolase. CpdB acts as a 3'-nucleotidase and as a phosphodiesterase of 2',3'-cyclic nucleotides and 3',5'-linear and cyclic dinucleotides. Both proteins are pro-virulent for the pathogens producing them and facilitate escape from the innate immunity of the infected host. Recently, the genomic distribution of cpdB-like genes in Bacteria was found to be non-homogeneous among different taxa, and differences occur within single taxa, even at species level. Similitudes and differences between UshA-like and CpdB-like proteins prompted parallel analysis of their genomic distributions in Bacteria. The presence of ushA-like and cpdB-like genes was tested by TBlastN analysis using seven protein probes to query the NCBI Complete Genomes Database. It is concluded that the distribution of ushA-like genes, like that of cpdB-like genes, is non-homogeneous. There is a partial correlation between both gene kinds: in some taxa, both are present or absent, while in others, only one is present. The result is an extensive catalog of the genomic distribution of these genes at different levels, from phylum to species, constituting a starting point for research using other in silico or experimental approaches.