Staphylococcus aureus MazG hydrolyzes oxidized guanine nucleotides and contributes to oxidative stress resistance.

We previously reported that knockout of the mazG (SA1292) gene decreases Staphylococcus aureus killing activity against silkworms. S. aureus MazG (SaMazG) has a nucleotide pyrophosphatase domain conserved among MazG family proteins, but its biochemical characteristics are unknown. In the present study, we purified recombinant N-terminal His-tagged SaMazG protein and examined its biochemical activity. SaMazG hydrolyzed GTP, UTP, dGTP, and TTP into nucleoside monophosphates. Hydrolytic activity of SaMazG against ATP, CTP, dATP, and dCTP was low or not detected. SaMazG exhibited high hydrolytic activity against 8-oxo-GTP and 8-oxo-dGTP, oxidized guanine nucleotides, with a Vmax/Km ratio more than 15-fold that of GTP. Furthermore, the S. aureus mazG knockout mutant was sensitive to hydrogen peroxide compared with the parent strain. These results suggest that SaMazG is a nucleotide pyrophosphatase hydrolyzing oxidized guanine nucleotides that contributes to the oxidative stress resistance of S. aureus.

Staphylococcus aureus aggregation in the plasma fraction of silkworm hemolymph.

Staphylococcus aureus formed bacterial aggregates in the plasma fraction of the hemolymph of silkworm, the larva of Bombyx mori, in a growth-dependent manner. The addition of arabinose or galactose inhibited the formation of S. aureus aggregates in the silkworm plasma. Formation of the bacterial aggregates depended on S. aureus genes required for the synthesis of bacterial surface polysaccharides-ypfP and ltaA, which are involved in lipoteichoic acid synthesis, and the tagO gene, which is involved in wall teichoic acid synthesis. These findings suggest that S. aureus forms bacterial aggregates in the silkworm plasma via bacterial surface teichoic acids.