STM2209-STM2208 (opvAB): A Phase Variation Locus of Salmonella enterica Involved in Control of O-Antigen Chain Length

Abstract

STM2209 and STM2208 are contiguous loci annotated as putative protein-coding genes in the chromosome of Salmonella enterica. Lack of homologs in related Enterobacteria and low G+C content suggest that S. enterica may have acquired STM2209-STM2208 by horizontal transfer. STM2209 and STM2208 are co-transcribed from a promoter upstream STM2209, and their products are inner (cytoplasmic) membrane proteins. Analysis with the bacterial adenylate cyclase two-hybrid system suggests that STM2209 and STM2208 may interact. Expression of STM2209-STM2208 is subjected to phase variation in wild type Salmonella enterica serovar Typhimurium. Switching frequencies in LB medium are 6.1×10−5 (OFF→ON) and 3.7×10−2 (ON→OFF) per cell and generation. Lack of DNA adenine methylation locks STM2209-STM2208 in the ON state, and lack of the LysR-type factor OxyR locks STM2209-STM2208 in the OFF state. OxyR-dependent activation of STM2209-STM2208 expression is independent of the oxidation state of OxyR. Salmonella cultures locked in the ON state show alteration of O-antigen length in the lipopolysaccharide, reduced absorption of bacteriophage P22, impaired resistance to serum, and reduced proliferation in macrophages. Phenotypic heterogeneity generated by STM2209-STM2208 phase variation may thus provide defense against phages. In turn, formation of a subpopulation unable to proliferate in macrophages may restrain Salmonella spread in animal organs, potentially contributing to successful infection.

Cell Cycle Constraints and Environmental Control of Local DNA Hypomethylation in α-Proteobacteria

“…By contrast, REC-Seq with a methylation sensitive restriction enzyme was used here to enrich for non-methylated sites in α-proteobacteria by Hin fI cleavage. The continuum of scores we detected in these experiments points towards the use of REC-Seq in detecting loci whose methylation is variable within a culture, for example phase variable loci [48, 49]. Hin fI REC-Seq revealed the occurrence of non-methylated GANTCs in at least two α-proteobacterial genomes.…”

Core Lipopolysaccharide-Specific Phage SSU5 as an Auxiliary Component of a Phage Cocktail for Salmonella Biocontrol

“…As an adaptive method to maintain an in vivo population, yet not enough to cause diseases in the host, S. Typhimurium 798 exhibited two phenotypes by phase switching: a nonadhesive phenotype containing short O-Ag and an adhesive phenotype possessing long O-Ag (46). The recently revealed phase-variable expression of STM2209-STM2208 genes in S. enterica, which was responsible for the phase-variable alteration of O-Ag chain length, might be involved in this phenotype switching (47). Notably, clones with short O-Ag by the phase variation of STM2209-STM2208 genes were resistant to the O-Ag-specific phage P22.…”

Programmed Heterogeneity: Epigenetic Mechanisms in Bacteria

“…These include the gtr switch on the P22 bacteriophage (86) and the chromosomal switch locus STM2209-STM2208 (opvAB) (87), each controlling modification of cell surface lipopolysaccharide of Salmonella, both of which are controlled by OxyR and Dam. In enteroaggregative E. coli, the sci1 type VI secretion system is controlled by a phase switch in which the iron regulatory protein Fur blocks Dam methylation of sci1 GATC sites, forming phase off and on methylation patterns (88).…”