Abstract
Streptococcus agalactiae (group B streptococcus, GBS) is a gram-positive bacterium that causes neonatal sepsis, pneumonia, and meningitis through maternal colonization and vertical transmission. During the search for the hippuricase gene, a potential diagnostic marker for GBS, a partial open reading frame was identified. Sequences analysis suggested that it is either a thiophene degradation factor or a novel GTPase in GBS. A full length copy of the gene was cloned and named thdF. Subsequently, assays such as triphenyl tetrazolium chloride (TTC) indicator plates, growth curve study, and GTPase/GTP-binding activity were carried out. We found that the ThdF protein indeed possesses an intrinsic GTPase activity that converts GTP into GDP and GMP. The optimal concentration of Mg2+ for the GTPase activity was around 10 mM. However, the activity of degrading thiophene derivatives was not observed. In addition, significant reduction in growth rate of the thdF overexpressed E. coli in the presence of thiophene-2-carboxylate was noted. These results indicate that instead of functioning as a thiophene degradation factor, ThdF is more likely to be a regulatory protein with GTP hydrolytic activity. The ThdF may somehow regulate the growth of GBS in responding to extracellular stresses, such as the presence of toxic chemicals.