σ ^B Regulates IS 256 -Mediated Staphylococcus aureus Biofilm Phenotypic Variation

Abstract

Biofilm formation in Staphylococcus aureus is subject to phase variation, and biofilm-negative derivatives emerge sporadically from a biofilm-positive bacterial population. To date, the only known mechanism for generating biofilm phenotypic variation in staphylococci is the reversible insertion/excision of IS256 in biofilmessential genes. In this study, we present evidence suggesting that the absence of the B transcription factor dramatically increases the rate of switching to the biofilm-negative phenotype in the clinical isolate S. aureus 15981, under both steady-state and flow conditions. The phenotypic switching correlates with a dramatic increase in the number of IS256 copies in the chromosomes of biofilm-negative variants, as well as with an augmented IS256 insertion frequency into the icaC and the sarA genes. IS256-mediated biofilm switching is reversible, and biofilm-positive variants could emerge from biofilm-negative B mutants. Analysis of the chromosomal insertion frequency using a recombinant IS256 element tagged with an erythromycin marker showed an almost three-times-higher transposition frequency in a ⌬ B strain. However, regulation of IS256 activity by B appears to be indirect, since transposase transcription is not affected in the absence of B and IS256 activity is inhibited to wild-type levels in a ⌬ B strain under NaCl stress. Overall, our results identify a new role for B as a negative regulator of insertion sequence transposition and support the idea that deregulation of IS256 activity abrogates biofilm formation capacity in S. aureus.

Influence of the σBStress Factor andyxaB, the Gene for a Putative Exopolysaccharide Synthase under σBControl, on Biofilm Formation

“…The synthesis of B is activated by diverse environmental and energy stresses and governs the transcription of a large set of general stress response genes (for a review, see reference 16). There are reports showing a direct contribution of B to the formation of adherent biofilms by Staphylococcus epidermidis and Staphylococcus aureus (22,23,37,43). Given these results, it was of interest to determine whether a B. subtilis sigB mutant (MM233) was able to form a biofilm under laboratory conditions.…”

Heterogeneity in Pseudomonas aeruginosa Biofilms Includes Expression of Ribosome Hibernation Factors in the Antibiotic-Tolerant Subpopulation and Hypoxia-Induced Stress Response in the Metabolically Active Population

“…Adaptive variability allows the cells to respond to their local environmental conditions (29,30,75). In addition, genetic alterations, including mutations, genetic recombination, and stochastic gene expression, have been identified as mechanisms that generate phenotypically and genetically distinct variant subpopulations within biofilms (2,7,9,12,20,25,27,34,41,42,67,76). Microscopic evidence has verified the presence of spatially segregated and differentially antibiotic susceptible sub-populations of cells (24,32,49).…”

Adaptation beyond the Stress Response: Cell Structure Dynamics and Population Heterogeneity in Staphylococcus aureus

“…The insertion of IS256 was suggested not to be random in the genome, because the formation of variants is observed only for the biofilm and protease phenotypes but not for others such as coagulase, hemolysin, and lipase (85). It is interesting that SigB regulates the frequency of IS256 transposition (85), though the precise mechanism is not known. In general, transposition is regulated/affected by a variety of host factors that differ depending on the mobile element (61).…”

“…Phase variation in the biofilm switch is mediated by the reversible insertion/excision of the insertion sequence, IS256, in biofilm essential genes such as the ica locus (40) and sarA (85). The insertion of IS256 was suggested not to be random in the genome, because the formation of variants is observed only for the biofilm and protease phenotypes but not for others such as coagulase, hemolysin, and lipase (85).…”

“…biofilm formation IS256 insertion in ica or sarA (40,85) protease activity (85) Other SJ duplication in sigH see Fig. 2 unpublished * a comprehensive list of phase variation in bacteria is available in reference (88).…”