초록
<P><I>Streptococcus sanguinis</I> is one of the most common agents of infective endocarditis. Spx proteins are a group of global regulators that negatively or positively control global transcription initiation. In this study, we characterized the <I>spxA1</I> gene in <I>S. sanguinis</I> SK36. The <I>spxA1</I> null mutant displayed opaque colony morphology, reduced hydrogen peroxide (H<SUB>2</SUB>O<SUB>2</SUB>) production, and reduced antagonistic activity against <I>Streptococcus mutans</I> UA159 relative to the wild type strain. The Δ<I>spxA1</I> mutant also demonstrated decreased tolerance to high temperature, acidic and oxidative stresses. Further analysis revealed that Δ<I>spxA1</I> also exhibited a ∼5-fold reduction in competitiveness in an animal model of endocarditis. Microarray studies indicated that expression of several oxidative stress genes was downregulated in the Δ<I>spxA1</I> mutant. The expression of <I>spxB</I> and <I>nox</I> was significantly decreased in the Δ<I>spxA1</I> mutant compared with the wild type. These results indicate that <I>spxA1</I> plays a major role in H<SUB>2</SUB>O<SUB>2</SUB> production, stress tolerance and endocarditis virulence in <I>S. sanguinis</I> SK36. The second <I>spx</I> gene, <I>spxA2,</I> was also found in <I>S. sanguinis</I> SK36. The <I>spxA2</I> null mutant was found to be defective for growth under normal conditions and showed sensitivity to high temperature, acidic and oxidative stresses.</P>