Identification of glyoxalase A in group B <i>Streptococcus</i> and its contribution to methylglyoxal tolerance and virulence

Abstract

Group B <i>Streptococcus</i> (GBS) is a Gram-positive pathobiont that commonly colonizes the gastrointestinal and lower female genital tracts but can cause sepsis and pneumonia in newborns and is a leading cause of neonatal meningitis. Despite the resulting disease severity, the pathogenesis of GBS is not completely understood, especially during the early phases of infection. To investigate GBS factors necessary for bloodstream survival, we performed a transposon (Tn) mutant screen in our bacteremia infection model using a GBS <i>mariner</i> transposon mutant library previously developed by our group. We identified significantly underrepresented mutations in 623 genes that contribute to survival in the blood, including those encoding known virulence factors such as capsule, the β-hemolysin, and inorganic metal ion transport systems. Most of the underrepresented genes have not been previously characterized or studied in GBS, including <i>gloA</i> and <i>gloB,</i> which are homologs for genes involved in methylglyoxal (MG) detoxification. MG is a byproduct of glycolysis and a highly reactive toxic aldehyde that is elevated in immune cells during infection. Here, we observed MG sensitivity across multiple GBS isolates and confirmed that <i>gloA</i> contributes to MG tolerance and invasive GBS infection. We show specifically that <i>gloA</i> contributes to GBS survival in the presence of neutrophils and depleting neutrophils in mice abrogates the decreased survival and infection of the <i>gloA</i> mutant. The requirement of the glyoxalase pathway during GBS infection suggests that MG detoxification is important for bacterial survival during host-pathogen interactions.IMPORTANCEA transposon-mutant screen of group B <i>Streptococcus</i> (GBS) in a bacteremia mouse model of infection revealed virulence factors known to be important for GBS survival such as the capsule, β-hemolysin/cytolysin, and genes involved in metal homeostasis. Many uncharacterized factors were also identified including genes that are part of the metabolic pathway that breaks down methylglyoxal (MG). The glyoxalase pathway is the most ubiquitous metabolic pathway for MG breakdown and is only a two-step process using glyoxalase A (<i>gloA</i>) and B (<i>gloB</i>) enzymes. MG is a highly reactive byproduct of glycolysis and is made by most cells. Here, we show that in GBS, the first enzyme in the glyoxalase pathway, encoded by <i>gloA</i>, contributes to MG resistance and blood survival. We further demonstrate that GloA contributes to GBS survival against neutrophils <i>in vitro</i> and <i>in vivo</i> and, therefore, is an important virulence factor required for invasive infection.