A small RNA from <i>Streptococcus suis</i> epidemic ST7 strain promotes bacterial survival in host blood and brain by enhancing oxidative stress resistance

<i>Streptococcus suis</i> is a Gram-positive pathogen causing septicaemia and meningitis in pigs and humans. However, how <i>S. suis</i> maintains a high bacterial load in the blood and brain is poorly understood. In this study, we found that a small RNA rss03 is predominantly present in <i>S. suis</i>, <i>Streptococcus parasuis</i>, and <i>Streptococcus ruminantium</i>, implying a conserved biological function. rss03 with a size of 303 nt mainly exists in <i>S. suis</i> sequence type (ST) 1 and epidemic ST7 strains that are responsible for human infections in China. Using MS2-affinity purification coupled with RNA sequencing (MAPS), proteomics analysis, and CopraRNA prediction, 14 direct targets of rss03 from an ST7 strain were identified. These direct targets mainly involve substance transport, transcriptional regulation, rRNA modification, and stress response. A more detailed analysis reveals that rss03 interacts with the coding region of <i>glpF</i> mRNA, and unexpectedly rss03 protects <i>glpF</i> mRNA from degradation by RNase J1. The GlpF protein is an aquaporin, contributes to <i>S. suis</i> oxidative stress resistance by H₂O₂ efflux, and facilitates bacterial survival in murine macrophages RAW264.7. Finally, we showed that rss03 and GlpF are required to maintain a high bacterial load in mouse blood and brain. Our study presents the first sRNA targetome in streptococci, enriches the knowledge of sRNA regulation in streptococci, and identifies pathways contributing to <i>S. suis</i> pathogenesis.