Spx Is a Global Effector Impacting Stress Tolerance and Biofilm Formation inStaphylococcus aureus

Abstract

In Bacillus subtilis, Spx was recently characterized as a novel type of global regulator whose activity is regulated by the redox status of the cells. In the present study, we demonstrate that inactivation of Spx in the important pathogen Staphylococcus aureus renders the cells hypersensitive to a wide range of stress conditions including high and low temperature, high osmolarity, and hydrogen peroxide. Moreover, growth was restricted under nonstress conditions. Two-dimensional gel electrophoresis revealed that the proteome of the spx mutant differs substantially from the proteome of wild-type cells, supporting the finding that Spx is also a global regulator in S. aureus. More specifically, we demonstrated that Spx is required for transcription of trxB, encoding thioredoxin reductase, under all growth conditions examined. As trxB is essential in S. aureus, we speculate that the severely reduced trxB transcription could account for some of the growth defects of the spx mutant. Inactivation of spx also enhanced biofilm formation. S. aureus biofilm formation is associated with the production of the polysaccharide intercellular adhesin encoded by the ica operon. Interestingly, our data indicate that the augmented capacity of the spx mutant to form biofilms is due to Spx modulating the expression of icaR, encoding a repressor of the structural ica genes (icaABCD). In summary, we conclude that Spx fulfills an important role for growth, general stress protection, and biofilm formation in S. aureus.

Role of Clp Proteins in Expression of Virulence Properties ofStreptococcus mutans

“…In B. subtilis, the inactivation of the transcriptional regulator Spx, a known target of ClpXP proteolysis, suppressed phenotypes associated with clpP or clpX mutations, including poor growth, genetic competence, and sporulation frequency (34). Similar findings have been made in L. lactis and S. aureus (19,36), suggesting that the linkage of Spx accumulation with ClpXP phenotypes may be conserved between low-GC GPB. Here, we showed that the mutation of either of two spx orthologs, named spxA and spxB, was responsible, at least in part, for the attenuation of phenotypes associated with the loss of ClpXP proteolysis in S. mutans.…”

“…More recently, Spx was shown to affect growth, general stress tolerance, and biofilm formation in S. aureus (36). Notably, unsuccessful attempts to isolate a clpP spx double mutant in S. aureus were reported, suggesting that the strain was not viable (36). The finding of the dual Spx regulators is particularly novel and may have broader implications since two or more copies of putative spx genes are also found in the genome of related streptococci, enterococci, and lactococci.…”

“…In L. monocytogenes, an spx homologue was found upregulated during the intracellular growth of the bacteria, suggesting that Spx might play a role in intracellular invasion, survival, or both (11). More recently, Spx was shown to affect growth, general stress tolerance, and biofilm formation in S. aureus (36). Notably, unsuccessful attempts to isolate a clpP spx double mutant in S. aureus were reported, suggesting that the strain was not viable (36).…”

SpxB Regulates O-Acetylation-dependent Resistance of Lactococcus lactis Peptidoglycan to Hydrolysis

“…Spx of S. aureus was recently shown to fulfill an important role in growth, general stress protection, and biofilm formation (56). The existence of several Spx-like paralogs in a bacterium may indicate that competitive (or synergistic) interactions between these proteins and RpoA in response to cell envelope stress may be a general phenomenon.…”

Staphylococcus aureus Biofilm Metabolism and the Influence of Arginine on Polysaccharide Intercellular Adhesin Synthesis, Biofilm Formation, and Pathogenesis

“…Due to the importance of S. aureus biofilms in medical device-associated infections, a considerable amount of research has been directed at understanding the mechanisms of biofilm formation. Much of this research has focused on the bacterial mediators of biofilm formation (41,43,56,59), the environmental effectors of biofilm formation (26,28,50), and, more recently, the global changes that occur during biofilm development (2,44,45,60). The consensus from transcriptional profiling studies of S. aureus biofilms is that bacteria are growing microaerobically or anaerobically relative to planktonic cultures (2,45).…”