Sau42I, a BcgI-like restriction-modification system encoded by the Staphylococcus aureus quadruple-converting phage...

Area of Science:

• Microbiology
• Bacteriology
• Molecular Biology

Background:

• Staphylococcus aureus phage Phi42 is a triple-converting bacteriophage with known genetic conversions.
• The mechanism behind Phi42's resistance to lysis by exogenous phages remained undetermined.
• Phage Phi42 influences host gene expression and confers resistance to specific typing phages.

Purpose of the Study:

• To elucidate the molecular basis of Phi42's resistance to lysis by International Basic Set (IBS) typing phages.
• To characterize the novel genetic element responsible for this phage resistance.
• To confirm the classification of Phi42 as a quadruple-converting phage.

Main Methods:

• Cloning and sequencing of genes within the Phi42 genome potentially involved in phage resistance.
• Expression of cloned genes in Staphylococcus aureus transformants.
• Assessing phage resistance phenotype of transformants.
• In vitro characterization of the encoded enzyme activity.

Main Results:

• Phage Phi42 encodes a novel restriction-modification (R-M) system, Sau42I, comprising ORF S and ORF RM.
• Expression of both Sau42I ORFs in S. aureus conferred resistance to all 23 IBS phages.
• Sau42I exhibits endonuclease activity dependent on Mg(2+) and S-adenosylmethionine, optimized at pH 8.
• This study confirms Phi42 as a quadruple-converting phage, the first described for S. aureus.

Conclusions:

• The Sau42I R-M system is responsible for Phi42's resistance to lysis by S. aureus typing phages.
• Phi42 represents a unique example of a quadruple-converting phage in S. aureus.
• The discovery of Sau42I provides new insights into phage-host interactions and bacterial defense mechanisms.