Copper Stress Induces a Global Stress Response in Staphylococcus aureus and Represses sae and agr Expression and Biofilm Formation

Abstract

Copper is an important cofactor for many enzymes; however, high levels of copper are toxic. Therefore, bacteria must ensure there is sufficient copper for use as a cofactor but, more importantly, must limit free intracellular levels to prevent toxicity. In this study, we have used DNA microarray to identify Staphylococcus aureus copper-responsive genes. Transcriptional profiling of S. aureus SH1000 grown in excess copper identified a number of genes which fall into four groups, suggesting that S. aureus has four main mechanisms for adapting to high levels of environmental copper, as follows: (i) induction of direct copper homeostasis mechanisms; (ii) increased oxidative stress resistance; (iii) expression of the misfolded protein response; and (iv) repression of a number of transporters and global regulators such as Agr and Sae. Our experimental data confirm that resistance to oxidative stress and particularly to H 2 O 2 scavenging is an important S. aureus copper resistance mechanism. Our previous studies have demonstrated that Eap and Emp proteins, which are positively regulated by Agr and Sae, are required for biofilm formation under low-iron growth conditions. Our transcriptional analysis has confirmed that sae, agr, and eap are repressed under high-copper conditions and that biofilm formation is indeed repressed under high-copper conditions. Therefore, our results may provide an explanation for how copper films can prevent biofilm formation on catheters.

Copper Tolerance and Characterization of a Copper-Responsive Operon, copYAZ , in an M1T1 Clinical Strain of Streptococcus pyogenes

“…The copper-mediated repression of biofilm formation has been seen with other Gram-positive bacteria such as Staphylococcus aureus (74) and S. mutans (75). The addition of as little as 1 M copper is able to inhibit S. aureus biofilm formation (74). The authors of that study suggested that the effect was due to copper repression of the positive biofilm regulators Agr and Sae (74).…”

“…How do biofilms provide protection against copper-mediated killing of S. pyogenes? The copper-mediated repression of biofilm formation has been seen with other Gram-positive bacteria such as Staphylococcus aureus (74) and S. mutans (75). The addition of as little as 1 M copper is able to inhibit S. aureus biofilm formation (74).…”

“…The addition of as little as 1 M copper is able to inhibit S. aureus biofilm formation (74). The authors of that study suggested that the effect was due to copper repression of the positive biofilm regulators Agr and Sae (74). In S. mutans, copper exposure alters the expression of glucosyltransferase, a key enzyme necessary for the adhesion and formation of biofilms on the tooth surface (75).…”

Control of Copper Resistance and Inorganic Sulfur Metabolism by Paralogous Regulators in Staphylococcus aureus

“…Recent findings suggest that alterations in sulfur metabolism influence the ability of Sau to form biofilms, an essential feature of its ability to thrive both inside and outside of the host (32). Microarray experiments carried out on mid-log liquid cultures of S. aureus SH1000 reveal that copper stress, sufficient to induce the CsoR-dependent expression of copA and perhaps other genes that function in oxidative stress resistance (25), negatively regulates biofilm formation via repression of the sae and agr regulons (52). Thus, CsoR and CstR-related stress response pathways may be physiologically linked by a connection to alteration in biofilm formation and oxidative stress and ultimately viability in the vertebrate host.…”

“…On the other hand, the gene encoding the likely copper chaperone CopZ just downstream from copA (Fig. 1A) is induced by copper (24,25), but may not be co-transcribed with copA (24). Although it is not yet known whether the transcription of copZ is also regulated by CsoR, inspection of the intergenic region between copA and copZ does not reveal an obvious candidate CsoR binding site like that found in the copA operator-promoter region, nor have we determined if copZ transcription is altered in the ⌬csoR strain.…”