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?Sa3mw Prophage as a Molecular Regulatory Switch of Staphylococcus aureus ?-Toxin Production.

ABSTRACT: Phage regulatory switches (phage-RSs) are a newly described form of active lysogeny where prophages function as regulatory mechanisms for expression of chromosomal bacterial genes. In Staphylococcus aureus, ?Sa3int is a widely distributed family of prophages that integrate into the ?-toxin structural gene hlb, effectively inactivating it. However, ?-toxin-producing strains often arise during infections and are more virulent in experimental infective endocarditis and pneumonia infections. We present evidence that in S. aureus MW2, ?Sa3mw excision is temporally and differentially responsive to growth conditions relevant to S. aureus pathogenesis. PCR analyses of ?Sa3mw (integrated and excised) and of intact hlb showed that ?Sa3mw preferentially excises in response to hydrogen peroxide-induced oxidative stress and during biofilm growth. ?Sa3mw remains as a prophage when in contact with human aortic endothelial cells in culture. A criterion for a prophage to be considered a phage-RS is the inability to lyse host cells. MW2 grown under phage-inducing conditions did not release infectious phage particles by plaque assay or transmission electron microscopy, indicating that ?Sa3mw does not carry out a productive lytic cycle. These studies highlight a dynamic, and perhaps more sophisticated, S. aureus-prophage interaction where ?Sa3int prophages provide a novel regulatory mechanism for the conditional expression of virulence factors.IMPORTANCE ?-Toxin is a sphingomyelinase hemolysin that significantly contributes to Staphylococcus aureus pathogenesis. In most S. aureus isolates the prophage ?Sa3int inserts into the ?-toxin gene hlb, inactivating it, but human and experimental infections give rise to ?-toxin-producing variants. However, it remained to be established whether ?Sa3mw excises in response to specific environmental cues, restoring the ?-toxin gene sequence. This is not only of fundamental interest but also critical when designing intervention strategies and therapeutics. We provide evidence that ?Sa3mw actively excises, allowing the conditional expression of ?-toxin. ?Sa3int prophages may play a novel and largely uncharacterized role in S. aureus pathogenesis as molecular regulatory switches that promote bacterial fitness and adaptation to the challenges presented by the mammalian host.

SUBMITTER: Tran PM

PROVIDER: S-EPMC6597384 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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ϕSa3mw Prophage as a Molecular Regulatory Switch of Staphylococcus aureus β-Toxin Production.

Tran Phuong M PM Feiss Michael M Kinney Kyle J KJ Salgado-Pabón Wilmara W

Journal of bacteriology 20190621 14

Phage regulatory switches (phage-RSs) are a newly described form of active lysogeny where prophages function as regulatory mechanisms for expression of chromosomal bacterial genes. In <i>Staphylococcus aureus</i>, ϕSa3int is a widely distributed family of prophages that integrate into the β-toxin structural gene <i>hlb</i>, effectively inactivating it. However, β-toxin-producing strains often arise during infections and are more virulent in experimental infective endocarditis and pneumonia infec ...[more]

PMID: 30962356

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Project description:Nicotinamide adenosine dinucleotide (NAD) has been found to be covalently attached to the 5' ends of specific RNAs in many different organisms, but the physiological consequences of this modification are largely unknown. Here, we report the occurrence of several NAD-RNAs in the opportunistic pathogen Staphylococcus aureus Most prominently, RNAIII, a central quorum-sensing regulator of this bacterium's physiology, was found to be 5' NAD capped in a range from 10 to 35%. NAD incorporation efficiency into RNAIII was found to depend in vivo on the -1 position of the P3 promoter. An increase in RNAIII's NAD content led to a decreased expression of alpha- and delta-toxins, resulting in reduced cytotoxicity of the modified strains. These effects seem to be caused neither by changes in RNAIII's secondary structure nor by a different translatability upon NAD attachment, as indicated by unaltered patterns in in vitro chemical probing and toeprinting experiments. Even though we did not observe any effect of this modification on RNAIII's secondary structure or translatability in vitro, additional unidentified factors might account for the modulation of exotoxins in vivo Ultimately, the study constitutes a step forward in the discovery of new roles of the NAD molecule in bacteria.IMPORTANCE Numerous organisms, including bacteria, are endowed with a 5' NAD cap in specific RNAs. While the presence of the 5' NAD cap modulates the stability of the modified RNA species, a significant biological function and phenotype have not been assigned so far. Here, we show the presence of a 5' NAD cap in RNAIII from S. aureus, a dual-function regulatory RNA involved in quorum-sensing processes and regulation of virulence factor expression. We also demonstrate that altering the natural NAD modification ratio of RNAIII leads to a decrease in exotoxin production, thereby modulating the bacterium's virulence. Our work unveils a new layer of regulation of RNAIII and the agr system that might be linked to the redox state of the NAD molecule in the cell.

Dataset Information

?Sa3mw Prophage as a Molecular Regulatory Switch of Staphylococcus aureus ?-Toxin Production.

Publications

ϕSa3mw Prophage as a Molecular Regulatory Switch of Staphylococcus aureus β-Toxin Production.

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