Molecular mechanisms and biological significance of the naturally occurring turnover of DSF-family quorum sensing signal in the phytopathogen Xanthomonas

Abstract:

Xanthomonas represents a range of bacterial species that cause diseases in a variety of crops. They produce and use DSF (Diffusible signaling factor)-family quorum sensing (QS) signal to sense cell population to regulate the expression of virulence genes. At post-logic growth phase, the levels of DSF-family signal decreased rapidly, indicating a naturally occurring signal turnover phenomenon in Xanthomonas. The expression levels of rpfB that encodes a putative fatty acyl CoA ligase, significantly increased at logarithmic growth phase. Deletion of rpfB significantly increased the production of DSF-family signal. Therefore, RpfB is involved in the degradation of DSF-family signals, including Xcc to exit from the quorum sensing phase at post-QS phase. DSF-family signal negatively regulates rpfB expression via rpfC/rpfG two-component signaling system, cyclic di-GMP and the global regulator Clp. The RpfB-dependent naturally DSF turnover system is present in a range of bacterial species, representing a conserved mechanism for QS signal turnover. However, the RpfB-regulated biological roles differ from species to species.

Key words:Xanthomonas;quorum sensing;naturally occurring signal turnover;DSF;RpfB