Metabolic and transcriptomic profiling of Streptococcus intermedius during aerobic and anaerobic growth

Streptococcus intermedius, S. constellatus, and S. anginosus comprise the Streptococcus Milleri/Anginosus group (SMG). They are facultative anaerobic bacteria that asymptomatically colonize the upper respiratory, gastrointestinal and urogenital tracts. They are also common pathogens in pyogenic invasive infections, as well as pulmonary and urinary tract infections. Most SMG infections are polymicrobial and associated with co-infecting obligate anaerobic bacteria. To better understand the effect of oxygen on the growth and physiology of these organisms, we compared the global metabolomic and transcriptomic profiles of S. intermedius strain B196 under aerobic and anaerobic conditions. The largest transcriptional changes were associated with induction of oxidative stress response genes under aerobic conditions. Modest changes in expression of genes associated with primary metabolism were observed under the two conditions. Intracellular and extracellular metabolites were measured using HILIC–LCMS. Differences in the abundance of specific metabolites were correlated with observed transcription changes in genes associated with their metabolism, implying that metabolism is primarily regulated at the transcriptional level. Rather than a large shift in primary metabolism under anaerobic conditions our results suggest a modest tuning of metabolism to support the accelerated growth rate of S. intermedius strain B196 in the absence of oxygen. For example, under anaerobic conditions, purine metabolism, pyrimidine de novo synthesis and pyrimidine salvage pathways were up-regulated at metabolic and transcriptional levels. This study provides a better understanding of differences between S. intermedius anaerobic and aerobic metabolism. The results reflect the organism’s predilection for anaerobic growth consistent with its pathogenic association with anaerobes in polymicrobial infections.