Quorum sensing inPseudomonas syringaepv.actinidiae(Psa)

Abstract

Quorum sensing (QS) is a complex bacterial intra and interspecific communication system that is regulated by signaling molecules produced by cell density-dependent mechanisms. QS may regulate different phenotypes such as virulence, motility and biofilm production. The aim of this research was to investigate the existence of a QS system in Pseudomonas syringae pv. actinidiae (Psa). Psa lacks the canonical QS system based on N-acyl homoserine lactone (AHL) production and detection. However, at least three signal receptors (PsaR1, PsaR2, PsaR3) were recently identified. The present study was conducted in order to clarify the effects of different cell densities on the intraspecific communication in Psa cultures, and the interspecific interaction between Psa and other bacteria associated with the plant host (i.e. in the phyllosphere) or known to have an active QS system. A bioinformatic research was conducted for the identification of genes putatively involved in Psa QS system. About 30 genes were selected due to their involvement in influencing specific phenotypes such as virulence, density perception, biofilm formation and motility. Motility and biofilm formation are crucial phenotypes in the early stages of host colonization under the control of QS circuitries. The experiments conducted demonstrated Psa ability to produce biofilm in LB liquid media depending on population density. Psa motility resulted particularly enhanced in the supernatants of bacteria with a AHL-based QS system, such as Pseudomonas fluorescens, or an AHL-overproducing strain of Pseudomonas putida. Quantitative expression of QS-related genes was analyzed by qPCR. In conclusion, from our preliminary studies we observed that QS-phenotypes seem to be influenced not only by the cell density, but also by the microbial community that may share the same environment with Psa. Presumably, only by considering the multiple interactions with both the plant host and other bacterial species, the functionality of Psa QS-system will be fully elucidated.