Effects of RNase III rncS Gene Deletion on Stress Response, Biofilm Formation and Virulence of Listeria monocytogenes

The ribonuclease III (RNase Ill) is an important enzyme system that regulates non-coding RNA (ncRNA) levels. In this study, LM-Delta rncS gene deletion strain was investigated by gene overlap extension PCR (SOE-PCR) and homologous recombination techniques. The environmental stress response, biofilm formation and virulence were determined and compared between the deletion strain LM-Delta rncS and the parental strain LM EGD-e. When compared with LM EGD-e, the adaptability of LM-Delta rncS was significantly reduced (P<0.05) under the stress of 30 degrees C/42 degrees C, pH 9, 5% NaCI, 3.8% ethanol and 0.1% H2O2. Biofilm formation ability of LM-Delta rncS was significantly lower (P<0.05) than that of LM EGD-e. In LM-AmcS, the transcription levels of ncRNA SreA and SbrA genes were significantly decreased (P<0.05). The adhesion rate and invasion rate of LM-Delta rncS in RAW264.7 cells were significantly lower (P<0.01) than those of LM EGD-e, and the survival and proliferation of LM-Delta rncS in RAW264.7 cells were also significantly decreased (P<0.05). Moreover, the transcription levels of InlA, hly, prfA and SigmaB gene were significantly lower (P<0.05) than those of LM EGD-e. LD50 of LM-Delta rncS in BALB/c mice was increased by 1.49 logarithmic orders, and the survival time of the mice was significantly prolonged when compared with LM EGD-e. In addition, the bacterial load in the liver and spleen was markedly decreased, and its pathological damage was also reduced. This study confirmed that RNase III RncS is involved in the regulation of environmental stress response, biofilm formation and virulence in LMd.