Summary auto-generated
This study investigates how the sigma factor RpoS regulates VanT, a quorum-sensing master regulator in the marine bacterium Vibrio anguillarum. Researchers used Western blot analysis, gene fusions with unstable green fluorescent protein, and RNA stability assays to demonstrate that RpoS induces VanT expression post-transcriptionally during late exponential growth, despite vanT mRNA abundance remaining relatively constant across growth phases. RpoS stabilizes vanT mRNA by repressing expression of Hfq, an RNA chaperone that normally destabilizes vanT mRNA via small regulatory RNAs (sRNAs). Critically, RpoS operates independently of the quorum-sensing phosphorelay system—it does not regulate VanO (the sigma-54 dependent activator) and is not regulated by the quorum-sensing cascade. Both VanT and RpoS were required for survival following UV irradiation and for production of pigment and metalloproteases. The findings reveal that RpoS and quorum-sensing systems act synergistically to modulate VanT expression, enabling the bacterium to coordinate stress responses and virulence factor production during stationary phase.
Key findings
- RpoS stabilizes vanT mRNA post-transcriptionally by repressing Hfq expression, inducing VanT protein during late exponential growth
- RpoS operates independently of the quorum-sensing phosphorelay system and is not regulated by VanO or the quorum-sensing cascade
- VanT and RpoS are both required for UV survival and production of pigment and metalloproteases
- The sigma factor RpoS works synergistically with quorum-sensing systems to regulate VanT expression and physiological responses
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Abstract
In vibrios, regulation of the Vibrio harveyi-like LuxR transcriptional activators occurs post-transcriptionally via small regulatory RNAs (sRNAs) that destabilize the luxR mRNA at a low cell population, eliminating expression of LuxR. Expression of the sRNAs is modulated by the vibrio quorum-sensing phosphorelay systems. However, vanT mRNA, which encodes a LuxR homologue in Vibrio anguillarum, is abundant at low and high cell density, indicating that VanT expression may be regulated via additional mechanisms. In this study, Western analyses showed that VanT was expressed throughout growth with a peak of expression during late exponential growth. VanO induced partial destabilization of vanT mRNA via activation of at least one Qrr sRNA. Interestingly, the sigma factor RpoS significantly stabilized vanT mRNA and induced VanT expression during late exponential growth. This induction was in part due to RpoS repressing expression of Hfq, an RNA chaperone. RpoS is not part of the quorum-sensing regulatory cascade since RpoS did not regulate expression or activity of VanO, and RpoS was not regulated by VanO or VanT. VanT and RpoS were needed for survival following UV irradiation and for pigment and metalloprotease production, suggesting that RpoS works with the quorum-sensing systems to modulate expression of VanT, which regulates survival and stress responses.