P2-154 Comparative Expression Analysis of Two Thermostable Nuclease Genes in Staphylococcus aureus

Tuesday, July 24, 2012
Exhibit Hall (Rhode Island Convention Center)
Yu Hu, Shanghai Jiao Tong University-Dept of Food Science, Shanghai, China
YanPing Xie, Shanghai Jiao Tong University-Dept of Food Science, Shanghai, China
Juni Tang, Southwest University for Nationalities, Chengdu, China
Xianming Shi, Shanghai Jiao Tong University, Shanghai, China
Introduction: Thermonuclease is known as a specific virulence factor in Staphylococcus aureus. A remarkable tolerance to prolonged heating and storage is exhibited by staphylococcal thermonuclease in foods and broth, and its presence is closely related with the occurrence of enterotoxins in food poisoning outbreaks. Previous studies have revealed the existence of two functional thermostable nucleases encoded by two different genes (nuc1 and nuc2) in S. aureus.

Purpose: To understand how these two thermonuclease genes are regulated in different strains of S. aureus, expression characteristics of both two genes are required.

Methods: Comparative mRNA analysis of nuc1 and nuc2 was carried out by Taqman-based real-time PCR. Toluidine blue DNA agar and spectrophotometric assay were used for thermonuclease activity test.

Results: Distinct expression patterns were observed at different growth stages, and expression was under the control of the sae regulatory system in strain RN4220. Maximum level of nuc1 transcripts was at the post-exponential growth phase, and expression was down-regulated 24 fold at late-exponential phase in a sae mutant. In contrast, nuc2 transcript levels declined after the early exponential phase, and it was 1.4 fold up-regulated in the sae mutant. Furthermore, unlike the expression of nuc1 that varied in three different S. aureus clinical strains, the transcription of nuc2 remained relatively constant. The nuc1 transcription level correlated well with thermonuclease activity results, which suggest that nuc1 plays a primary role in thermonuclease activity in S.aureus.

Significance: This information will be useful for understanding thermonuclease gene function and alterations of regulation for pathogenesis and food poisoning of S. aureus.