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Hu H, Liu H, Kweon O, Hart ME. A naturally occurring point mutation in the hyaluronidase gene ( hysA1) of Staphylococcus aureus UAMS-1 results in reduced enzymatic activity. Can J Microbiol 2021; 68:1-13. [PMID: 34520677 DOI: 10.1139/cjm-2021-0110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hyaluronic acid is a high-molecular-weight polysaccharide that is widely distributed in animal tissues. Bacterial hyaluronidases degrade hyaluronic acid as secreted enzymes and have been shown to contribute to infection. Staphylococcus aureus UAMS-1 is a clinical isolate that codes for two hyaluronidases (hysA1 and hysA2). Previous research has shown the presence of a full-length HysA1 protein from the S. aureus UAMS-1 strain with no evidence of enzymatic activity. In this study, the coding and upstream promoter regions of hysA1 from the S. aureus UAMS-1 strain were cloned, sequenced, and compared to the hysA1 gene from the S. aureus Sanger 252 strain. A single base change resulting in an E480G amino acid change was identified in the hysA1 gene from the S. aureus UAMS-1 strain when compared to the hysA1 gene from S. aureus Sanger 252. A plasmid copy of hysA1 from S. aureus Sanger 252 transduced into an S. aureus UAMS-1 hysA2 deletion mutant strain restored near wild-type levels of enzymatic activity. Homology modeling of the HysA1 hyaluronidase was performed with SWISS-MODEL using hyaluronidase from Streptococcus pneumoniae as the template, followed by a series of structural analyses using PyMOL, PLIP, PDBsum, and HOPE servers. This glutamic acid is highly conserved among hyaluronidases from Staphylococcus and other gram-positive bacteria. A series of structural analyses suggested that Glu-480 in HysA1 is critically responsible for maintaining the structural and functional ensemble of the catalytic and tunnel-forming residues, which are essential for enzyme activity. The missense mutation of Glu-480 to Gly introduces a loss of side chain hydrogen bond interactions with key residues Arg-360 and Arg-364, which are responsible for the tunnel topology, resulting in displacement of the substrate from an ideal position for catalysis through a localized conformational change of the active site. There is a high degree of relatedness among several gram-positive bacterial hyaluronidases; the loss of enzymatic activity of HysA1 in the S. aureus UAMS-1 strain is most likely caused by the mutation identified in our study. The role of hyaluronidase in staphylococcal infection and the redundancy of this gene are yet to be determined.
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Affiliation(s)
- Haijing Hu
- Office of Dietary Supplement Programs, Center for Food Safety and Nutrition, U.S. Food and Drug Administration, College Park, MD 20740, USA
| | - Huanli Liu
- Branch of Microbiology, Arkansas Laboratory, Office of Regulatory Affairs, U.S. Food and Drug Administration, Jefferson, AR 72079, USA
| | - Ohgew Kweon
- Division of Microbiology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR 72079, USA
| | - Mark E Hart
- Division of Microbiology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR 72079, USA
- Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
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Inhibition of exotoxin production by mobile genetic element SCCmec-encoded psm-mec RNA is conserved in staphylococcal species. PLoS One 2014; 9:e100260. [PMID: 24926994 PMCID: PMC4057442 DOI: 10.1371/journal.pone.0100260] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 05/23/2014] [Indexed: 11/19/2022] Open
Abstract
Staphylococcal species acquire antibiotic resistance by incorporating the mobile-genetic element SCCmec. We previously found that SCCmec-encoded psm-mec RNA suppresses exotoxin production as a regulatory RNA, and the psm-mec translation product increases biofilm formation in Staphylococcus aureus. Here, we examined whether the regulatory role of psm-mec on host bacterial virulence properties is conserved among other staphylococcal species, S. epidermidis and S. haemolyticus, both of which are important causes of nosocomial infections. In S. epidermidis, introduction of psm-mec decreased the production of cytolytic toxins called phenol-soluble modulins (PSMs) and increased biofilm formation. Introduction of psm-mec with a stop-codon mutation that did not express PSM-mec protein but did express psm-mec RNA also decreased PSM production, but did not increase biofilm formation. Thus, the psm-mec RNA inhibits PSM production, whereas the PSM-mec protein increases biofilm formation in S. epidermidis. In S. haemolyticus, introduction of psm-mec decreased PSM production, but did not affect biofilm formation. The mutated psm-mec with a stop-codon also caused the same effect. Thus, the psm-mec RNA also inhibits PSM production in S. haemolyticus. These findings suggest that the inhibitory role of psm-mec RNA on exotoxin production is conserved among staphylococcal species, although the stimulating effect of the psm-mec gene on biofilm formation is not conserved.
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Quorum-sensing agr mediates bacterial oxidation response via an intramolecular disulfide redox switch in the response regulator AgrA. Proc Natl Acad Sci U S A 2012; 109:9095-100. [PMID: 22586129 DOI: 10.1073/pnas.1200603109] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Oxidation sensing and quorum sensing significantly affect bacterial physiology and host-pathogen interactions. However, little attention has been paid to the cross-talk between these two seemingly orthogonal signaling pathways. Here we show that the quorum-sensing agr system has a built-in oxidation-sensing mechanism through an intramolecular disulfide switch possessed by the DNA-binding domain of the response regulator AgrA. Biochemical and mass spectrometric analysis revealed that oxidation induces the intracellular disulfide bond formation between Cys-199 and Cys-228, thus leading to dissociation of AgrA from DNA. Molecular dynamics (MD) simulations suggest that the disulfide bond formation generates a steric clash responsible for the abolished DNA binding of the oxidized AgrA. Mutagenesis studies further established that Cys-199 is crucial for oxidation sensing. The oxidation-sensing role of Cys-199 is further supported by the observation that the mutant Staphylococcus aureus strain expressing AgrAC199S is more susceptible to H(2)O(2) owing to repression of the antioxidant bsaA gene under oxidative stress. Together, our results show that oxidation sensing is a component of the quorum-sensing agr signaling system, which serves as an intrinsic checkpoint to ameliorate the oxidation burden caused by intense metabolic activity and potential host immune response.
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The YjbH adaptor protein enhances proteolysis of the transcriptional regulator Spx in Staphylococcus aureus. J Bacteriol 2011; 194:1186-94. [PMID: 22194450 DOI: 10.1128/jb.06414-11] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Spx is a global regulator that is widespread among the low-G+C-content gram-positive bacteria. Spx has been extensively studied in Bacillus subtilis, where it acts as an activator and a repressor of transcription in response to disulfide stress. Under nonstress conditions, Spx is rapidly degraded by the ClpXP protease. This degradation is enhanced by the YjbH adaptor protein. Upon disulfide stress, the amount of Spx rapidly increases due to a decrease in degradation. In the opportunistic pathogen Staphylococcus aureus, Spx is a global regulator influencing growth, biofilm formation, and general stress protection, and cells lacking the spx gene exhibit poor growth also under nonstress conditions. To investigate the mechanism by which the activity of Spx is regulated, we identified a homolog in S. aureus of the B. subtilis yjbH gene. The gene encodes a protein that shows approximately 30% sequence identity to YjbH of B. subtilis. Heterologous expression of S. aureus yjbH in a B. subtilis yjbH mutant restored Spx to wild-type levels both under nonstress conditions and under conditions of disulfide stress. From these studies, we conclude that the two YjbH homologues have a conserved physiological function. Accordingly, inactivation of yjbH in S. aureus increased the level of Spx protein and transcription of the Spx-regulated gene trxB. Notably, the yjbH mutant exhibited reduced growth and increased pigmentation, and both phenotypes were reversed by complementation of the yjbH gene.
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Cheung GYC, Duong AC, Otto M. Direct and synergistic hemolysis caused by Staphylococcus phenol-soluble modulins: implications for diagnosis and pathogenesis. Microbes Infect 2011; 14:380-6. [PMID: 22178792 DOI: 10.1016/j.micinf.2011.11.013] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 11/19/2011] [Accepted: 11/24/2011] [Indexed: 12/15/2022]
Abstract
Phenol-soluble modulins are secreted staphylococcal peptides with an amphipathic α-helical structure. Some PSMs are strongly cytolytic toward human neutrophils and represent major virulence determinants during Staphylococcus aureus skin and blood infection. However, capacities of PSMs to lyse human erythrocytes have not been investigated. Here, we demonstrate that many S. aureus and Staphylococcus epidermidis PSMs lyse human erythrocytes. Furthermore, synergism with S. aureus β-toxin considerably increased the hemolytic capacities of several PSMs. This synergism may be of key importance in PSM and β-toxin-producing S. aureus or in mixed-strain or -species infections with PSM and β-toxin producers. Of specific interest, several PSMs, in particular PSMα peptides, contributed to a considerable extent to synergistic hemolysis with β-toxin or when using the β-toxin-producing strain RN4220 in CAMP assays. Thus, CAMP-type assays should not be used to detect or quantify S. aureus δ-toxin production, but may be used for an overall assessment of Agr functionality. Our study suggests an additional role of PSMs in staphylococcal pathogenesis and demonstrates that the repertoire of staphylococcal hemolysins is not limited to S. aureus and is much larger and diverse than previously thought.
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Affiliation(s)
- Gordon Y C Cheung
- Pathogen Molecular Genetics Section, Laboratory of Human Bacterial Pathogenesis, National Institute of Allergy and Infectious Diseases, The National Institutes of Health, Bethesda, MD 20892, USA
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Sun F, Cho H, Jeong DW, Li C, He C, Bae T. Aureusimines in Staphylococcus aureus are not involved in virulence. PLoS One 2010; 5:e15703. [PMID: 21209955 PMCID: PMC3012096 DOI: 10.1371/journal.pone.0015703] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2010] [Accepted: 11/19/2010] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Recently, dipeptide aureusimines were reported to activate expression of staphylococcal virulence genes, such as alpha-hemolysin, and increase S. aureus virulence. Surprisingly, most of the virulence genes affected by aureusimines form part of the regulon of the SaeRS two component system (TCS), raising the possibility that SaeRS might be directly or indirectly involved in the aureusimine-dependent signaling process. METHODOLOGY/PRINCIPAL FINDINGS Using HPLC analyses, we confirmed that a transposon mutant of ausA, the gene encoding the aureusimine dipeptide synthesis enzyme, does not produce dipeptides. However, the transposon mutant showed normal hemolysis activity and alpha-hemolysin/SaeP production. Furthermore, the P1 promoter of the sae operon, one of the targets of the SaeRS TCS, showed normal transcription activity. Moreover, in contrast to the original report, the ausA transposon mutant did not exhibit attenuated virulence in an animal infection model. DNA sequencing revealed that the ausA deletion mutant used in the original study has an 83 nt-duplication in saeS. Hemolysis activity of the original mutant was restored by a plasmid carrying the sae operon. A mutant of the sae operon showed elevated resistance to chloramphenicol and erythromycin, two antibiotics widely used during staphylococcal mutagenesis. At 43°C in the presence of erythromycin and aeration, the conditions typically employed for staphylococcal mutagenesis, an saeR transposon mutant grew much faster than a control mutant and the saeR mutant was highly enriched in a mixed culture experiment. CONCLUSIONS/SIGNIFICANCE Our results show that the previously reported roles of aureusimines in staphylococcal gene regulation and virulence were due to an unintended mutation in saeS, which was likely selected due to elevated resistance of the mutant to environmental stresses. Thus, there is no evidence indicating that the dipeptide aureusimines play a role in sae-mediated virulence factor production or contribute to staphylococcal virulence.
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Affiliation(s)
- Fei Sun
- Department of Chemistry and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois, United States of America
| | - Hoonsik Cho
- Department of Microbiology and Immunology, Indiana University School of Medicine-Northwest, Gary, Indiana, United States of America
| | - Do-Won Jeong
- Department of Microbiology and Immunology, Indiana University School of Medicine-Northwest, Gary, Indiana, United States of America
| | - Chunling Li
- Department of Microbiology and Immunology, Indiana University School of Medicine-Northwest, Gary, Indiana, United States of America
| | - Chuan He
- Department of Chemistry and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois, United States of America
- * E-mail: (CH); (TB)
| | - Taeok Bae
- Department of Microbiology and Immunology, Indiana University School of Medicine-Northwest, Gary, Indiana, United States of America
- * E-mail: (CH); (TB)
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Abstract
The important human pathogen Staphylococcus aureus is known to spread on soft agar plates. Here, we show that colony spreading of S. aureus involves the agr quorum-sensing system. This finding can be related to the agr-dependent expression of biosurfactants, such as phenol-soluble modulins, suggesting a connection between spreading motility and virulence.
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Nielsen JS, Christiansen MHG, Bonde M, Gottschalk S, Frees D, Thomsen LE, Kallipolitis BH. Searching for small σB-regulated genes in Staphylococcus aureus. Arch Microbiol 2010; 193:23-34. [DOI: 10.1007/s00203-010-0641-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 08/25/2010] [Accepted: 09/09/2010] [Indexed: 02/05/2023]
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The chaperone ClpX stimulates expression of Staphylococcus aureus protein A by Rot dependent and independent pathways. PLoS One 2010; 5:e12752. [PMID: 20856878 PMCID: PMC2939077 DOI: 10.1371/journal.pone.0012752] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Accepted: 08/20/2010] [Indexed: 12/26/2022] Open
Abstract
The Clp ATPases (Hsp100) constitute a family of closely related proteins that have protein reactivating and remodelling activities typical of molecular chaperones. In Staphylococcus aureus the ClpX chaperone is essential for virulence and for transcription of spa encoding Protein A. The present study was undertaken to elucidate the mechanism by which ClpX stimulates expression of Protein A. For this purpose, we prepared antibodies directed against Rot, an activator of spa transcription, and demonstrated that cells devoid of ClpX contain three-fold less Rot than wild-type cells. By varying Rot expression from an inducible promoter we showed that expression of Protein A requires a threshold level of Rot. In the absence of ClpX the Rot content is reduced below this threshold level, hence, explaining the substantially reduced Protein A expression in the clpX mutant. Experiments addressed at pinpointing the role of ClpX in Rot synthesis revealed that ClpX is required for translation of Rot. Interestingly, translation of the spa mRNA was, like the rot mRNA, enhanced by ClpX. These data demonstrate that ClpX performs dual roles in regulating Protein A expression, as ClpX stimulates transcription of spa by enhancing translation of Rot, and that ClpX additionally is required for full translation of the spa mRNA. The current findings emphasize that ClpX has a central role in fine-tuning virulence regulation in S. aureus.
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Villaruz AE, Bubeck Wardenburg J, Khan BA, Whitney AR, Sturdevant DE, Gardner DJ, DeLeo FR, Otto M. A point mutation in the agr locus rather than expression of the Panton-Valentine leukocidin caused previously reported phenotypes in Staphylococcus aureus pneumonia and gene regulation. J Infect Dis 2009; 200:724-34. [PMID: 19604047 DOI: 10.1086/604728] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
sThe role of Panton-Valentine leukocidin (PVL) in Staphylococcus aureus pathogenesis is controversial. Here, we show that an unintended point mutation in the agr P2 promoter of S. aureus caused the phenotypes in gene regulation and murine pneumonia attributed to PVL by earlier investigators. In agreement with other studies that failed to detect similar effects of PVL using community-associated methicillin-resistant S. aureus strains, we found no significant effect of PVL on gene expression or pathogenesis after we repaired the mutation. These findings provide further evidence that PVL does not have a major impact on S. aureus pathogenesis. Moreover, our results demonstrate that a single nucleotide polymorphism in an intergenic region can dramatically affect bacterial physiology and virulence. Finally, our work emphasizes the need to frequently evaluate the integrity of the S. aureus agr locus.
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Affiliation(s)
- Amer E Villaruz
- Laboratory of Human Bacterial Pathogenesis, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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Diep BA, Palazzolo-Ballance AM, Tattevin P, Basuino L, Braughton KR, Whitney AR, Chen L, Kreiswirth BN, Otto M, DeLeo FR, Chambers HF. Contribution of Panton-Valentine leukocidin in community-associated methicillin-resistant Staphylococcus aureus pathogenesis. PLoS One 2008; 3:e3198. [PMID: 18787708 PMCID: PMC2527530 DOI: 10.1371/journal.pone.0003198] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2008] [Accepted: 08/22/2008] [Indexed: 11/20/2022] Open
Abstract
Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains typically carry genes encoding Panton-Valentine leukocidin (PVL). We used wild-type parental and isogenic PVL-deletion (Δpvl) strains of USA300 (LAC and SF8300) and USA400 (MW2) to test whether PVL alters global gene regulatory networks and contributes to pathogenesis of bacteremia, a hallmark feature of invasive staphylococcal disease. Microarray and proteomic analyses revealed that PVL does not alter gene or protein expression, thereby demonstrating that any contribution of PVL to CA-MRSA pathogenesis is not mediated through interference of global gene regulatory networks. Inasmuch as a direct role for PVL in CA-MRSA pathogenesis remains to be determined, we developed a rabbit bacteremia model of CA-MRSA infection to evaluate the effects of PVL. Following experimental infection of rabbits, an animal species whose granulocytes are more sensitive to the effects of PVL compared with the mouse, we found a contribution of PVL to pathogenesis over the time course of bacteremia. At 24 and 48 hours post infection, PVL appears to play a modest, but measurable role in pathogenesis during the early stages of bacteremic seeding of the kidney, the target organ from which bacteria were not cleared. However, the early survival advantage of this USA300 strain conferred by PVL was lost by 72 hours post infection. These data are consistent with the clinical presentation of rapid-onset, fulminant infection that has been associated with PVL-positive CA-MRSA strains. Taken together, our data indicate a modest and transient positive effect of PVL in the acute phase of bacteremia, thereby providing evidence that PVL contributes to CA-MRSA pathogenesis.
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Affiliation(s)
- Binh An Diep
- Division of Infectious Diseases, Department of Medicine, San Francisco General Hospital, University of California San Francisco, San Francisco, California, United States of America
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Nickerson NN, Joag V, McGavin MJ. Rapid autocatalytic activation of the M4 metalloprotease aureolysin is controlled by a conserved N-terminal fungalysin-thermolysin-propeptide domain. Mol Microbiol 2008; 69:1530-43. [DOI: 10.1111/j.1365-2958.2008.06384.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Jarry TM, Memmi G, Cheung AL. The expression of alpha-haemolysin is required forStaphylococcus aureusphagosomal escape after internalization in CFT-1 cells. Cell Microbiol 2008; 10:1801-14. [DOI: 10.1111/j.1462-5822.2008.01166.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Traber KE, Lee E, Benson S, Corrigan R, Cantera M, Shopsin B, Novick RP. agr function in clinical Staphylococcus aureus isolates. MICROBIOLOGY (READING, ENGLAND) 2008; 154:2265-2274. [PMID: 18667559 PMCID: PMC4904715 DOI: 10.1099/mic.0.2007/011874-0] [Citation(s) in RCA: 261] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The accessory gene regulator (agr) of Staphylococcus aureus is a global regulator of the staphylococcal virulon, which includes secreted virulence factors and surface proteins. The agr locus is important for virulence in a variety of animal models of infection, and has been assumed by inference to have a major role in human infection. Although most human clinical S. aureus isolates are agr(+), there have been several reports of agr-defective mutants isolated from infected patients. Since it is well known that the agr locus is genetically labile in vitro, we have addressed the question of whether the reported agr-defective mutants were involved in the infection or could have arisen during post-isolation handling. We obtained a series of new staphylococcal isolates from local clinical infections and handled these with special care to avoid post-isolation mutations. Among these isolates, we found a number of strains with non-haemolytic phenotypes owing to mutations in the agr locus, and others with mutations elsewhere. We have also obtained isolates in which the population was continuously heterogeneous with respect to agr functionality, with agr(+) and agr(-) variants having otherwise indistinguishable chromosomal backgrounds. This finding suggested that the agr(-) variants arose by mutation during the course of the infection. Our results indicate that while most clinical isolates are haemolytic and agr(+), non-haemolytic and agr(-) strains are found in S. aureus infections, and that agr(+) and agr(-) variants may have a cooperative interaction in certain types of infections.
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Affiliation(s)
- Katrina E. Traber
- Molecular Pathogenesis Program and Department of Microbiology and Medicine, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute for Biomolecular Medicine, New York University School of Medicine, 540 First Avenue, NY 10016, USA
| | - Elsie Lee
- Molecular Pathogenesis Program and Department of Microbiology and Medicine, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute for Biomolecular Medicine, New York University School of Medicine, 540 First Avenue, NY 10016, USA
| | - Sarah Benson
- New York University School of Medicine, NY 10016, USA
| | | | | | - Bo Shopsin
- Division of Infectious Diseases, Department of Medicine, New York University School of Medicine, NY 10016, USA
| | - Richard P. Novick
- Molecular Pathogenesis Program and Department of Microbiology and Medicine, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute for Biomolecular Medicine, New York University School of Medicine, 540 First Avenue, NY 10016, USA
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Abstract
The Staphylococcus aureus svrA gene was identified in a signature-tagged mutagenesis screen for Tn917 insertions attenuated for mouse virulence, and subsequently found to be defective in agr expression. Its attenuation of virulence was attributed to its failure to express the agr regulon. In addition to the Tn917 insertion in svrA, the original svrA mutant strain (P6C63) has an adventitious frame-shift in agrC, which results in truncation of the AgrC peptide. Separation of the svrA mutation from the agrC frame-shift revealed that svrA has no detectable affect on agr activation, as assessed by exoprotein profiles and the production of haemolytic toxins. These results indicate that svrA does not play a role in Staphylococcus aureus infections via an agr-mediated pathway.
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Affiliation(s)
- John Chen
- Program in Molecular Pathogenesis, Skirball Institute, and Departments of Microbiology and Medicine, New York University Medical Center, New York 10016, USA
| | - Richard P Novick
- Program in Molecular Pathogenesis, Skirball Institute, and Departments of Microbiology and Medicine, New York University Medical Center, New York 10016, USA
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Nickerson NN, Prasad L, Jacob L, Delbaere LT, McGavin MJ. Activation of the SspA serine protease zymogen of Staphylococcus aureus proceeds through unique variations of a trypsinogen-like mechanism and is dependent on both autocatalytic and metalloprotease-specific processing. J Biol Chem 2007; 282:34129-38. [PMID: 17878159 DOI: 10.1074/jbc.m705672200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The serine and cysteine proteases SspA and SspB of Staphylococcus aureus are secreted as inactive zymogens, zSspA and zSspB. Mature SspA is a trypsin-like glutamyl endopeptidase and is required to activate zSspB. Although a metalloprotease Aureolysin (Aur) is in turn thought to contribute to activation of zSspA, a specific role has not been demonstrated. We found that pre-zSspA is processed by signal peptidase at ANA(29) downward arrow, releasing a Leu(30) isoform that is first processed exclusively through autocatalytic intramolecular cleavage within a glutamine-rich propeptide segment, (40)QQTQSSKQQTPKIQ(53). The preferred site is Gln(43) with secondary processing at Gln(47) and Gln(53). This initial processing is necessary for optimal and subsequent Aur-dependent processing at Leu(58) and then Val(69) to release mature SspA. Although processing by Aur is rate-limiting in zSspA activation, the first active molecules of Val(69)SspA promote rapid intermolecular processing of remaining zSspA at Glu(65), producing an N-terminal (66)HANVILP isoform that is inactive until removal of the HAN tripeptide by Aur. Modeling indicated that His(66) of this penultimate isoform blocks the active site by hydrogen bonding to Ser(237) and occlusion of substrate. Binding of glutamate within the active site of zSspA is energetically unfavorable, but glutamine fits into the primary specificity pocket and is predicted to hydrogen bond to Thr(232) proximal to Ser(237), permitting autocatalytic cleavage of the glutamine-rich propeptide segment. These and other observations suggest that zSspA is activated through a trypsinogen-like mechanism where supplementary features of the propeptide must be sequentially processed in the correct order to allow efficient activation.
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Affiliation(s)
- Nicholas N Nickerson
- Department of Laboratory Medicine and Pathobiology, University of Toronto Sunnybrook Health Science Centre, Toronto, Ontario, Canada
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Shaw LN, Jonsson IM, Singh VK, Tarkowski A, Stewart GC. Inactivation of traP has no effect on the agr quorum-sensing system or virulence of Staphylococcus aureus. Infect Immun 2007; 75:4519-27. [PMID: 17548478 PMCID: PMC1951194 DOI: 10.1128/iai.00491-07] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The success of Staphylococcus aureus as a pathogen can largely be attributed to the plethora of genetic regulators encoded within its genome that temporally regulate its arsenal of virulence determinants throughout its virulence lifestyle. Arguably the most important of these is the two-component, quorum-sensing system agr. Over the last decade, the controversial presence of a second quorum-sensing system (the TRAP system) has been proposed, and it has been mooted to function as the master regulator of virulence in S. aureus by modulating agr. Mutants defective in TRAP are reported to be devoid of agr expression, lacking in hemolytic activity, essentially deficient in the secretion of virulence determinants, and avirulent in infection models. A number of research groups have questioned the validity of the TRAP findings in recent years; however, a thorough and independent analysis of its role in S. aureus physiology and pathogenesis has not been forthcoming. Therefore, we have undertaken such an analysis of the TRAP locus of S. aureus. We found that a traP mutant was equally hemolytic as the wild-type strain. Furthermore, transcriptional profiling found no alterations in the traP mutant in expression levels of agr or in expression levels of multiple agr-regulated genes (hla, sspA, and spa). Analysis of secreted and surface proteins of the traP mutant revealed no deviation in comparison to the parent. Finally, analysis conducted using a murine model of S. aureus septic arthritis revealed that, in contrast to an agr mutant, the traP mutant was just as virulent as the wild-type strain.
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Affiliation(s)
- Lindsey N Shaw
- Department of Veterinary Pathobiology, University of Missouri, Columbia, MO 65211, USA
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Pamp SJ, Frees D, Engelmann S, Hecker M, Ingmer H. Spx is a global effector impacting stress tolerance and biofilm formation in Staphylococcus aureus. J Bacteriol 2006; 188:4861-70. [PMID: 16788195 PMCID: PMC1483011 DOI: 10.1128/jb.00194-06] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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.
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Affiliation(s)
- Sünje Johanna Pamp
- Department of Veterinary Pathobiology, Royal Veterinary and Agricultural University (KVL), Stigbøjlen 4, DK-1870 Frederiksberg C, Denmark
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Traber K, Novick R. A slipped-mispairing mutation in AgrA of laboratory strains and clinical isolates results in delayed activation of agr and failure to translate delta- and alpha-haemolysins. Mol Microbiol 2006; 59:1519-30. [PMID: 16468992 DOI: 10.1111/j.1365-2958.2006.04986.x] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
agr is a global regulator of staphylococcal virulence and other accessory gene functions, especially including the haemolysins. Lack of haemolysin production therefore generally represents a defect in agr function. An example of this is Staphylococcus aureus strain RN4220, a widely used laboratory strain that carries a nitrosoguanidine (MNNG)-induced mutation enabling it to accept DNA from Escherichia coli and other bacteria. We show here that the non-haemolytic phenotype of RN4220 is caused by an extra A residue in a run of seven As at the 3' end of agrA (agrA-8A). This causes a frameshift that results in the addition of three amino acyl residues to the C-terminal end of the protein. The 8A mutation does not inactivate the agr locus, but rather delays agr activation by 2-3 h, which results in failure to translate alpha- and delta-haemolysins, and hence, in a non-haemolytic phenotype. This mutation turned out not to be an adventitious consequence of MNNG mutagenesis, but rather had arisen in RN450, the immediate parent of RN4220. RN450 had become haemolytically heterogeneous in storage, and its non-haemolytic variants had the 8A mutation. The same mutation was also identified in a clinical isolate in which a non-haemolytic variant had arisen during the course of infection. Haemolytic activity in the mutant laboratory strains could be restored by the addition of auto-inducing peptide (AIP) early in growth, indicating that delayed production of RNAIII is responsible for the failure to translate alpha- and delta-haemolysins. Discovery of the 8A mutation has revealed the basis of the dissociation between agr activity and the non-haemolytic phenotype of RN4220, and has solved the long-standing mystery of the variable non-haemolytic phenotype of its immediate parent, RN450. The occurrence of this mutation in a clinical isolate indicates that it is not simply a laboratory phenomenon, and may represent a naturally occurring mechanism for the modulation of agr activity.
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Affiliation(s)
- Katrina Traber
- Molecular Pathogenesis Program and Department of Microbiology and Medicine, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
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Bayer AS, McNamara P, Yeaman MR, Lucindo N, Jones T, Cheung AL, Sahl HG, Proctor RA. Transposon disruption of the complex I NADH oxidoreductase gene (snoD) in Staphylococcus aureus is associated with reduced susceptibility to the microbicidal activity of thrombin-induced platelet microbicidal protein 1. J Bacteriol 2006; 188:211-22. [PMID: 16352837 PMCID: PMC1317573 DOI: 10.1128/jb.188.1.211-222.2006] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2005] [Accepted: 10/02/2005] [Indexed: 11/20/2022] Open
Abstract
The cationic molecule thrombin-induced platelet microbicidal protein 1 (tPMP-1) exerts potent activity against Staphylococcus aureus. We previously reported that a Tn551 S. aureus transposon mutant, ISP479R, and two bacteriophage back-transductants, TxA and TxB, exhibit reduced in vitro susceptibility to tPMP-1 (tPMP-1(r)) compared to the parental strain, ISP479C (V. Dhawan, M. R. Yeaman, A. L. Cheung, E. Kim, P. M. Sullam, and A. S. Bayer, Infect. Immun. 65:3293-3299, 1997). In the current study, the genetic basis for tPMP-1(r) in these mutants was identified. GenBank homology searches using sequence corresponding to chromosomal DNA flanking Tn551 mutant strains showed that the fourth gene in the staphylococcal mnh operon (mnhABCDEFG) was insertionally inactivated. This operon was previously reported to encode a Na(+)/H(+) antiporter involved in pH tolerance and halotolerance. However, the capacity of ISP479R to grow at pH extremes and in high NaCl concentrations (1 to 3 M), coupled with its loss of transmembrane potential (DeltaPsi) during postexponential growth, suggested that the mnh gene products are not functioning as a secondary (i.e., passive) Na(+)/H(+) antiporter. Moreover, we identified protein homologies between mnhD and the nuo genes of Escherichia coli that encode components of a complex I NADH:ubiquinone oxidoreductase. Consistent with these data, exposures of tPMP-1-susceptible (tPMP-1(s)) parental strains (both clinical and laboratory derived) with either CCCP (a proton ionophore which collapses the proton motive force) or pieracidin A (a specific complex I enzyme inhibitor) significantly reduced tPMP-induced killing to levels seen in the tPMP-1(r) mutants. To reflect the energization of the gene products encoded by the mnh operon, we have renamed the locus sno (S. aureus nuo orthologue). These novel findings indicate that disruption of a complex I enzyme locus can confer reduced in vitro susceptibility to tPMP-1 in S. aureus.
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Affiliation(s)
- Arnold S Bayer
- Department of Medical Microbiology & Immunology, University of Wisconsin, 1300 University Avenue, Biochemistry Building, Room 250, Madison, WI 53706, USA
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Frees D, Chastanet A, Qazi S, Sørensen K, Hill P, Msadek T, Ingmer H. Clp ATPases are required for stress tolerance, intracellular replication and biofilm formation in Staphylococcus aureus. Mol Microbiol 2005; 54:1445-62. [PMID: 15554981 DOI: 10.1111/j.1365-2958.2004.04368.x] [Citation(s) in RCA: 236] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The Hsp100/Clp ATPases constitute a family of closely related proteins of which some members function solely as chaperones whereas others additionally can associate with the unrelated ClpP peptidase forming a Clp proteolytic complex. We have investigated the role of four Clp ATPases in the versatile pathogen, Staphylococcus aureus. Previously, we showed that ClpX is required for expression of major virulence factors and for virulence of S. aureus, but not for survival during heat shock. In the present study, we have inactivated clpC, clpB and clpL and, while none of these mutations affected toxin production, both ClpC and ClpB and to a minor extent ClpL were required for intracellular multiplication within bovine mammary epithelial cells. These defects were paralleled by an inability of the clpC mutant to grow at high temperature and of the clpB mutant to induce thermotolerance indicating that the protective functions of these proteins are required both at high temperature and during infection. By primer extension analysis and footprint studies, we show that expression of clpC and clpB is controlled by the negative heat-shock regulator, CtsR, and that ClpC is required for its repressor activity. Thus, ClpC is a likely sensor of stress encountered during both environmental stress and infection. In addition to virulence factor production the ability to form biofilms is of importance to S. aureus as a nosocomial pathogen. Interestingly, biofilm formation was reduced in the absence of ClpX or ClpC whereas it was enhanced in the absence of ClpP. Thus, our data show that Clp proteolytic complexes and the Clp ATPases control several key processes of importance to the success of S. aureus as a pathogen.
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Affiliation(s)
- Dorte Frees
- Department of Veterinary Pathobiology, Royal Veterinary and Agricultural University (KVL), Stigbøjlen 4, DK-1870 Frederiksberg C, Denmark
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Gomes AR, Vinga S, Zavolan M, de Lencastre H. Analysis of the genetic variability of virulence-related loci in epidemic clones of methicillin-resistant Staphylococcus aureus. Antimicrob Agents Chemother 2005; 49:366-79. [PMID: 15616317 PMCID: PMC538922 DOI: 10.1128/aac.49.1.366-379.2005] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) isolates have previously been classified into major epidemic clonal types by pulsed-field gel electrophoresis in combination with multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec typing. We aimed to investigate whether genetic variability in potentially polymorphic domains of virulence-related factors could provide another level of differentiation in a diverse collection of epidemic MRSA clones. The target regions of strains representative of epidemic clones and genetically related methicillin-susceptible S. aureus isolates from the 1960s that were sequenced included the R domains of clfA and clfB; the D, W, and M regions of fnbA and fnbB; and three regions in the agr operon. Sequence variation ranged from very conserved regions, such as those for RNAIII and the agr interpromoter region, to the highly polymorphic R regions of the clf genes. The sequences of the clf R domains could be grouped into six major sequence types on the basis of the sequences in their 3' regions. Six sequence types were also observed for the fnb sequences at the amino acid level. From an evolutionary point of view, it was interesting that a small DNA stretch at the 3' clf R-domain sequence and the fnb sequences agreed with the results of MLST for this set of strains. In particular, clfB R-domain sequences, which had a high discriminatory capacity and with which the types distinguished were congruent with those obtained by other molecular typing methods, have potential for use for the typing of S. aureus. Clone- and strain-specific sequence motifs in the clf and fnb genes may represent useful additions to a typing methodology with a DNA array.
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Affiliation(s)
- A R Gomes
- Laboratory of Molecular Genetics, Universidade Nova de Lisboa, Oeiras, Portugal
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Schwan WR, Langhorne MH, Ritchie HD, Stover CK. Loss of hemolysin expression in Staphylococcus aureus agr mutants correlates with selective survival during mixed infections in murine abscesses and wounds. FEMS IMMUNOLOGY AND MEDICAL MICROBIOLOGY 2003; 38:23-8. [PMID: 12900051 DOI: 10.1016/s0928-8244(03)00098-1] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
During the screening of a Staphylococcus aureus signature-tagged mutagenesis library, it was noted that nonhemolytic bacteria became more abundant as time passed in murine abscess and wound models, but not within organ tissues associated with systemic infections. To examine this further, a mixed population of hyperhemolytic, hemolytic, and nonhemolytic S. aureus strain RN6390 cells were inoculated into mice using abscess, wound, and systemic models of infection. After 7 days in the abscess, the hyperhemolytic group markedly declined, whereas the nonhemolytic population increased significantly. A similar phenomenon occurred in murine wounds, but not during the systemic infection. Sequencing of several of the signature-tagged mutants indicated mutations in the agrC gene or within the agrA-agrC intergenic region. Both alpha-hemolysin and delta-hemolysin activity was curtailed in these mutants, but beta-hemolysin activity was unaffected. Single strain comparisons between wild-type strain 8325-4 and strain DU1090 (hla-) as well as between strain RN6911 (agr) and wild-type strain RN6390 were performed using the same three animal models of infection. The agr mutant strain and the hla mutant strain showed no difference in bacterial counts in murine wounds compared to their respective parent strains. The same held true in murine abscesses at day 4, but strain RN6911 counts then declined at day 7. Considerable clearing of the hla mutant strain and the agr mutant strain occurred in the systemic model of infection. Mixed infections with the DU1090 and 8325-4 strains in the abscess model showed a slight advantage given to the DU1090 population, but a distinct selection for the parental 8325-4 strain in the liver. These results suggest that agr mutations cause reductions in the expression of several secreted proteins, including alpha- and delta-hemolysin, which in turn contribute to a growth advantage of this agr mutant group within a mixed population of S. aureus cells residing in abscesses and wounds.
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Affiliation(s)
- William R Schwan
- Department of Microbiology, University of Wisconsin-La Crosse, 1725 State St., La Crosse, WI 54601, USA.
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Somerville GA, Saïd-Salim B, Wickman JM, Raffel SJ, Kreiswirth BN, Musser JM. Correlation of acetate catabolism and growth yield in Staphylococcus aureus: implications for host-pathogen interactions. Infect Immun 2003; 71:4724-32. [PMID: 12874354 PMCID: PMC166023 DOI: 10.1128/iai.71.8.4724-4732.2003] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recently, we reported that the prototypical Staphylococcus aureus strain RN6390 (a derivative of NCTC 8325) had significantly reduced aconitase activity relative to a diverse group of S. aureus isolates, leading to the hypothesis that strain RN6390 has impaired tricarboxylic acid (TCA) cycle-mediated acetate catabolism. Analysis of the culture supernatant from RN6390 confirmed that acetate was incompletely catabolized, suggesting that the ability to catabolize acetate can be lost by S. aureus. To test this hypothesis, we examined the carbon catabolism of the S. aureus strains whose genome sequences are publicly available. All strains catabolized glucose and excreted acetate into the culture medium. However, strains NCTC 8325 and N315 failed to catabolize acetate during the postexponential growth phase, resulting in significantly lower growth yields relative to strains that catabolized acetate. Strains NCTC 8325 and RN6390 contained an 11-bp deletion in rsbU, the gene encoding a positive regulator of the alternative sigma factor sigma(B) encoded by sigB. An isogenic derivative strain of RN6390 containing the wild-type rsbU gene had significantly increased acetate catabolism, demonstrating that sigma(B) is required for acetate catabolism. Taken together, the data suggest that naturally occurring mutations can alter the ability of S. aureus to catabolize acetate, a surprising discovery, as TCA cycle function has been demonstrated to be involved in the virulence, survival, and persistence of several pathogenic organisms. Additionally, these mutations decrease the fitness of S. aureus by reducing the number of progeny placed into subsequent generations, suggesting that in certain situations a decreased growth yield is advantageous.
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Affiliation(s)
- Greg A Somerville
- Laboratory of Human Bacterial Pathogenesis, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana 59840, USA.
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Frees D, Qazi SNA, Hill PJ, Ingmer H. Alternative roles of ClpX and ClpP in Staphylococcus aureus stress tolerance and virulence. Mol Microbiol 2003; 48:1565-78. [PMID: 12791139 DOI: 10.1046/j.1365-2958.2003.03524.x] [Citation(s) in RCA: 241] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Clp proteolytic complexes are essential for virulence and for survival under stress conditions in several pathogenic bacteria. Recently, a study using signature-tagged mutagenesis identified the ClpX ATPase as also being required for virulence in Staphylococcus aureus. Presently, we have constructed deletion mutants removing either ClpX or the proteolytic subunit, ClpP, in S. aureus 8325-4 in order to examine a putative link between stress tolerance and virulence. When exposed to stress, we found that, although clpP mutant cells were sensitive to conditions generating misfolded proteins, the absence of ClpX improved survival. In the presence of oxidative stress or at low temperature, both ClpP and ClpX were important for growth. Virulence was examined in a murine skin abscess model and was found to be severely attenuated for both mutants. S. aureus pathogenicity is largely dependent on a set of extracellular and cell wall-associated proteins. In the mutant cells, the amount of alpha-haemolysin (hla) and several other extracellular proteins was greatly decreased, and analysis of hla expression revealed that the reduction occurred at the transcriptional level. Essential for transcriptional regulation of hla is the quorum-sensing agr locus. Interestingly, the absence of ClpX or ClpP reduced both transcription of the agr effector molecule, RNA III, and the activity of the autoinducing peptide (AIP). In addition, ClpX was required independently of ClpP for transcription of spa encoding Protein A. Thus, our results indicate that ClpX and ClpP contribute to virulence by controlling the activity of major virulence factors rather than by promoting stress tolerance.
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Affiliation(s)
- Dorte Frees
- Department of Veterinary Microbiology, Royal Veterinary and Agricultural University (KVL), Stigbøjlen 4, DK-1870 Frederiksberg C, Denmark
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26
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Somerville GA, Beres SB, Fitzgerald JR, DeLeo FR, Cole RL, Hoff JS, Musser JM. In vitro serial passage of Staphylococcus aureus: changes in physiology, virulence factor production, and agr nucleotide sequence. J Bacteriol 2002; 184:1430-7. [PMID: 11844774 PMCID: PMC134861 DOI: 10.1128/jb.184.5.1430-1437.2002] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recently, we observed that Staphylococcus aureus strains newly isolated from patients had twofold-higher aconitase activity than a strain passaged extensively in vitro, leading us to hypothesize that aconitase specific activity decreases over time during in vitro passage. To test this hypothesis, a strain recovered from a patient with toxic shock syndrome was serially passaged for 6 weeks, and the aconitase activity was measured. Aconitase specific activity decreased 38% (P < 0.001) by the sixth week in culture. During serial passage, S. aureus existed as a heterogeneous population with two colony types that had pronounced (wild type) or negligible zones of beta-hemolytic activity. The cell density-sensing accessory gene regulatory (agr) system regulates beta-hemolytic activity. Surprisingly, the percentage of colonies with a wild-type beta-hemolytic phenotype correlated strongly with aconitase specific activity (rho = 0.96), suggesting a common cause of the decreased aconitase specific activity and the variation in percentage of beta-hemolytic colonies. The loss of the beta-hemolytic phenotype also coincided with the occurrence of mutations in the agrC coding region or the intergenic region between agrC and agrA in the derivative strains. Our results demonstrate that in vitro growth is sufficient to result in mutations within the agr operon. Additionally, our results demonstrate that S. aureus undergoes significant phenotypic and genotypic changes during serial passage and suggest that vigilance should be used when extrapolating data obtained from the study of high-passage strains.
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Affiliation(s)
- Greg A Somerville
- Laboratory of Human Bacterial Pathogenesis, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases/NIH, 903 South 4th Street, Hamilton, Montana 59840, USA
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Valderas MW, Hart ME. Identification and characterization of a second superoxide dismutase gene (sodM) from Staphylococcus aureus. J Bacteriol 2001; 183:3399-407. [PMID: 11344148 PMCID: PMC99638 DOI: 10.1128/jb.183.11.3399-3407.2001] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A gene encoding superoxide dismutase (SOD), sodM, from S. aureus was cloned and characterized. The deduced amino acid sequence specifies a 187-amino-acid protein with 75% identity to the S. aureus SodA protein. Amino acid sequence comparisons with known SODs and relative insensitivity to hydrogen peroxide and potassium cyanide indicate that SodM most likely uses manganese (Mn) as a cofactor. The sodM gene expressed from a plasmid rescued an Escherichia coli double mutant (sodA sodB) under conditions that are otherwise lethal. SOD activity gels of S. aureus RN6390 whole-cell lysates revealed three closely migrating bands of activity. The two upper bands were absent in a sodM mutant, while the two lower bands were absent in a sodA mutant. Thus, the middle band of activity most likely represents a SodM-SodA hybrid protein. All three bands of activity increased as highly aerated cultures entered the late exponential phase of growth, SodM more so than SodA. Viability of the sodA and sodM sodA mutants but not the sodM mutant was drastically reduced under oxidative stress conditions generated by methyl viologen (MV) added during the early exponential phase of growth. However, only the viability of the sodM sodA mutant was reduced when MV was added during the late exponential and stationary phases of growth. These data indicate that while SodA may be the major SOD activity in S. aureus throughout all stages of growth, SodM, under oxidative stress, becomes a major source of activity during the late exponential and stationary phases of growth such that viability and growth of an S. aureus sodA mutant are maintained.
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Affiliation(s)
- M W Valderas
- Department of Molecular Biology and Immunology, University of North Texas Health Science Center at Fort Worth, 3500 Camp Bowie Blvd., Fort Worth, TX 76107-2699, USA
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Knobloch JK, Bartscht K, Sabottke A, Rohde H, Feucht HH, Mack D. Biofilm formation by Staphylococcus epidermidis depends on functional RsbU, an activator of the sigB operon: differential activation mechanisms due to ethanol and salt stress. J Bacteriol 2001; 183:2624-33. [PMID: 11274123 PMCID: PMC95180 DOI: 10.1128/jb.183.8.2624-2633.2001] [Citation(s) in RCA: 212] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2000] [Accepted: 01/04/2001] [Indexed: 11/20/2022] Open
Abstract
Staphylococcus epidermidis is a common pathogen in medical device-associated infections. Its major pathogenetic factor is the ability to form adherent biofilms. The polysaccharide intercellular adhesin (PIA), which is synthesized by the products of the icaADBC gene cluster, is essential for biofilm accumulation. In the present study, we characterized the gene locus inactivated by Tn917 insertions of two isogenic, icaADBC-independent, biofilm-negative mutants, M15 and M19, of the biofilm-producing bacterium S. epidermidis 1457. The insertion site was the same in both of the mutants and was located in the first gene, rsbU, of an operon highly homologous to the sigB operons of Staphylococcus aureus and Bacillus subtilis. Supplementation of Trypticase soy broth with NaCl (TSB(NaCl)) or ethanol (TSB(EtOH)), both of which are known activators of sigB, led to increased biofilm formation and PIA synthesis by S. epidermidis 1457. Insertion of Tn917 into rsbU, a positive regulator of alternative sigma factor sigma(B), led to a biofilm-negative phenotype and almost undetectable PIA production. Interestingly, in TSB(EtOH), the mutants were enabled to form a biofilm again with phenotypes similar to those of the wild type. In TSB(NaCl), the mutants still displayed a biofilm-negative phenotype. No difference in primary attachment between the mutants and the wild type was observed. Similar phenotypic changes were observed after transfer of the Tn917 insertion of mutant M15 to the independent and biofilm-producing strain S. epidermidis 8400. In 11 clinical S. epidermidis strains, a restriction fragment length polymorphism of the sigB operon was detected which was independent of the presence of the icaADBC locus and a biofilm-positive phenotype. Obviously, different mechanisms are operative in the regulation of PIA expression in stationary phase and under stress induced by salt or ethanol.
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Affiliation(s)
- J K Knobloch
- Institut für Medizinische Mikrobiologie und Immunologie, Universitätsklinikum Hamburg-Eppendorf, D-20246 Hamburg, Germany.
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McNamara PJ, Milligan-Monroe KC, Khalili S, Proctor RA. Identification, cloning, and initial characterization of rot, a locus encoding a regulator of virulence factor expression in Staphylococcus aureus. J Bacteriol 2000; 182:3197-203. [PMID: 10809700 PMCID: PMC94507 DOI: 10.1128/jb.182.11.3197-3203.2000] [Citation(s) in RCA: 152] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
A chromosomal insertion of transposon Tn917 partially restores the expression of protease and alpha-toxin activities to PM466, a genetically defined agr-null derivative of the wild-type Staphylococcus aureus strain RN6390. In co-transduction experiments, transposon-encoded erythromycin resistance and a protease- and alpha-toxin-positive phenotype are transferred at high frequency from mutant strains to agr-null strains of S. aureus. Southern analysis of chromosomal DNA and sequence analysis of DNA flanking the Tn917 insertion site in mutant strains revealed that the transposon interrupted a 498-bp open reading frame (ORF). Similarity searches using a conceptual translation of the ORF identified a region of homology to the known staphylococcal global regulators AgrA and SarA. To verify that the mutant allele conferred the observed phenotype, a wild-type allele of the mutant gene was introduced into the genome of a mutant strain by homologous recombination. The resulting isolates had a restored agr-null phenotype. Virulence factor gene expression in mutant, restored mutant, and wild-type strains was quantified by measuring alpha-toxin activity in culture supernatant fluids and by Northern analysis of the alpha-toxin transcript. We named this ORF rot (for repressor of toxins) (GenBank accession no. AF189239) because of the activity associated with rot::Tn917 mutant strains.
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Affiliation(s)
- P J McNamara
- Medical Microbiology and Immunology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
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Jaeger KE, Dijkstra BW, Reetz MT. Bacterial biocatalysts: molecular biology, three-dimensional structures, and biotechnological applications of lipases. Annu Rev Microbiol 1999; 53:315-51. [PMID: 10547694 DOI: 10.1146/annurev.micro.53.1.315] [Citation(s) in RCA: 718] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Bacteria produce and secrete lipases, which can catalyze both the hydrolysis and the synthesis of long-chain acylglycerols. These reactions usually proceed with high regioselectivity and enantioselectivity, and, therefore, lipases have become very important stereoselective biocatalysts used in organic chemistry. High-level production of these biocatalysts requires the understanding of the mechanisms underlying gene expression, folding, and secretion. Transcription of lipase genes may be regulated by quorum sensing and two-component systems; secretion can proceed either via the Sec-dependent general secretory pathway or via ABC transporters. In addition, some lipases need folding catalysts such as the lipase-specific foldases and disulfide-bond-forming proteins to achieve a secretion-competent conformation. Three-dimensional structures of bacterial lipases were solved to understand the catalytic mechanism of lipase reactions. Structural characteristics include an alpha/beta hydrolase fold, a catalytic triad consisting of a nucleophilic serine located in a highly conserved Gly-X-Ser-X-Gly pentapeptide, and an aspartate or glutamate residue that is hydrogen bonded to a histidine. Four substrate binding pockets were identified for triglycerides: an oxyanion hole and three pockets accommodating the fatty acids bound at position sn-1, sn-2, and sn-3. The differences in size and the hydrophilicity/hydrophobicity of these pockets determine the enantiopreference of a lipase. The understanding of structure-function relationships will enable researchers to tailor new lipases for biotechnological applications. At the same time, directed evolution in combination with appropriate screening systems will be used extensively as a novel approach to develop lipases with high stability and enantioselectivity.
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Affiliation(s)
- K E Jaeger
- Lehrstuhl Biologie der Mikroorganismen, Ruhr-Universität, Bochum, Germany.
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Wann ER, Fehringer AP, Ezepchuk YV, Schlievert PM, Bina P, Reiser RF, Höök MM, Leung DY. Staphylococcus aureus isolates from patients with Kawasaki disease express high levels of protein A. Infect Immun 1999; 67:4737-43. [PMID: 10456925 PMCID: PMC96803 DOI: 10.1128/iai.67.9.4737-4743.1999] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/1999] [Accepted: 06/30/1999] [Indexed: 01/28/2023] Open
Abstract
Kawasaki disease (KD) is an acute vasculitis of young children that can be complicated by coronary artery abnormalities. Recent findings suggest that a superantigen(s) may play an important role in stimulating the immune activation associated with the disease, although the origin of this superantigen(s) is unclear. Staphylococcus aureus, isolated from the rectum or pharynx of patients with KD, secretes toxic shock syndrome toxin 1 (TSST-1). The KD isolates express low levels of other exoproteins compared to isolates from patients with toxic shock syndrome (TSS). Thus, it was previously suggested that the KD isolates may be defective in the global regulatory locus agr (for accessory gene regulator), which positively regulates these factors (D. Y. M. Leung et al., Lancet 342:1385-1388, 1993). Here we describe another characteristic of KD isolates. When considered collectively, the KD isolates were found to express higher levels of staphylococcal protein A than the TSS isolates, another characteristic of an agr-defective phenotype. This correlated with a higher level of spa mRNA in these isolates. In contrast, the KD and TSS isolates expressed comparable levels of TSST-1, consistent with previous findings (D. Y. M. Leung et al., Lancet 342:1385-1388, 1993). Analysis of RNAIII transcript levels and nucleotide sequence analysis of the RNAIII-coding region suggested that the KD isolates are not defective in RNAIII, the effector molecule of the agr regulatory system. However, induction of RNAIII transcription in the KD isolates did not result in a dramatic decrease in the amount of spa mRNA, as has been reported for other strains (F. Vandenesch, J. Kornblum, and R. P. Novick, J. Bacteriol. 173:6313-6320, 1991).
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Affiliation(s)
- E R Wann
- Albert A. Alkek Institute of Biosciences and Technology, Texas A & M University Health Science Center, Houston, Texas 77030-3303, USA
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