Co-transcriptomic analysis of group A Streptococcus (GAS; Streptococcus pyogenes) invasions of human endothelial cells

Group A Streptococcus (GAS, aka Streptococcus pyogenes) causes an array of human diseases from mild pharyngitis to life-threatening necrotizing fasciitis. Invading host cells is a strategy for GAS to avoid antibiotic killing and immune system clearance. Our previous study showed that GAS is able to multiply in human microvascular endothelial cell line-1 (HMEC-1), and has higher survival in HMEC-1 cells due to insufficient acidification in lysosomes. GAS peroxide response regulator (PerR) modulates not only peroxide stress, but also metal homeostasis and bacterial virulence. Therefore, we aimed to investigate the role of PerR during GAS invading endothelial cells. First, we found that ΔperR mutant was more tolerant to H2O2 in vitro using hydrogen peroxide sensitivity assay. We further used cDNA-qPCR analysis to clarify the resistance mechanism of ΔperR mutant. The gene expressions of dpr, ahpC, and ahpF were up-regulated, explaining the enhanced resistance of the ΔperR mutant against peroxide stress. However, the proliferation of the ΔperR mutant in HMEC-1 cells was significantly lower than wild type strain after 5 h post-infection. To explore the underlying mechanisms of ΔperR mutant during infection, we performed dual RNAseq analysis to identify differentially expressed genes, and validated them using cDNA-qPCR analysis. The resulting up-regulated genes of iron efflux pump pmtA, iron/zinc chelating protein dpr, and zinc acquisition system (adcA, lmb/adcAII, phtD), and down-regulated zinc efflux pump czcD gave rise to impaired metal homeostasis in the ΔperR mutant. Furthermore, in vitro growth curve assays showed that the ΔperR mutant was sensitive to zinc deficiency and resistant to zinc toxicity. Taken together, this study has demonstrated the critical roles that GAS PerR plays in protecting from peroxide stress of host innate immune responses and zinc sequestration of nutritional immunity. Our novel findings open a new avenue of strategies in the development of antimicrobial agents. Our study demonstrates the importance of PerR. It aids GAS virulence in immune evasion during the LC3-associated phagocytosis in endothelial cells.