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

## TL;DR

A small RNA in a harmful Streptococcus suis strain helps the bacteria survive in the host's blood and brain by improving resistance to stress.

## Contribution

The first sRNA targetome in streptococci is presented, revealing novel regulatory mechanisms in S. suis.

## Key findings

- The sRNA rss03 is conserved in several streptococcal species and is prevalent in epidemic S. suis ST7 strains.
- rss03 protects glpF mRNA from degradation, enhancing oxidative stress resistance and bacterial survival in macrophages.
- rss03 and GlpF are essential for maintaining high bacterial loads in mouse blood and brain.

## Abstract

Streptococcus suis is a Gram-positive pathogen causing septicaemia and meningitis in pigs and humans. However, how S. suis 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 S. suis, Streptococcus parasuis, and Streptococcus ruminantium, implying a conserved biological function. rss03 with a size of 303 nt mainly exists in S. suis 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 glpF mRNA, and unexpectedly rss03 protects glpF mRNA from degradation by RNase J1. The GlpF protein is an aquaporin, contributes to S. suis 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 S. suis pathogenesis.