Quorum-sensing systems trigger catalase expression to reverse the oxyR deletion-mediated VBNC state in Salmonella typhimurium

OxyR is an important regulatory protein that plays a key role in anti-oxygenation, and its deletion causes a special VBNC (Viable But Non-Culturable) state in many bacteria including Salmonella typhimurium. The S. typhimurium in the VBNC state can grow in LB broth but cannot grow on an LB plate unless its concentration is sufficiently high. However, the mechanism that reverses this state is not clear. In this study, conditioned media containing autoinducer collected from the wild type strain can restore the growth of low concentrations of the oxyR mutant strain on LB plates, and S. typhimurium collected from the plate has higher catalase activity than that from the broth, suggesting that a quorum-sensing system can trigger catalase expression to resuscitate the organism from the VBNC state independent of the OxyR regulon. We discovered a novel catalase (STM14_2049, Cat) whose expression is strictly concentration-dependent. The purified Cat protein has obvious catalase activity in vitro and in vivo and can restore the growth of the low concentration oxyR mutant strain. Thus, we believed Cat plays a role in VBNC resuscitation process. By understanding this mechanism, we can further understand the antioxidation and quorum-sensing systems in Salmonella typhimurium.