Pseudomonas putida strain PCL1445 produces two cyclic lipopeptides, named putisolvins I and II, which represent a Novel class of biosurfactants. Putisolvins reduce the surface tension between... Show morePseudomonas putida strain PCL1445 produces two cyclic lipopeptides, named putisolvins I and II, which represent a Novel class of biosurfactants. Putisolvins reduce the surface tension between liquid and air, and disrupt already existing biofilms of several Pseudomonas sp., including those of the opportunistic human pathogen P. aeruginosa, and therefore offers opportunities for interesting application in the medical and industrial field. In this Ph.D Thesis, I describe the regulation of cyclic lipopeptide biosynthesis in P. putida. A dnaK gene and a GacA/GacS two-component signalling system were discovered and were shown to be involved in biosurfactants production. Given that DnaK is a heat-chock protein, we investigated the role of temperature on putisolvin production. The results showed that biosurfactant production in P. putida is up-regulated at low temperatures and that DnaK is required for putisolvin production. Bacteria co-ordinate their activities by producing and detecting small diffusible signal molecules (N-acylhomoserine lactones) which enable a population of organized bacteria to act as a community by forming a biofilm. Such a co-operative behaviour is named “quorum sensing” and plays a central role in the lifestyle of bacteria. P. putida PCL1445 was shown to produce N-acylhomoserine lactones which control the production of putisolvins and regulate biofilm formation. We hypothesise that the bacterial community co-ordinates the biosynthesis of putisolvin when nutrients become limiting resulting in a detachment of part of the bacterial cell population. In this Ph.D Thesis, Novel mechanisms for the regulation of cyclic lipopeptide biosynthesis are described, which contribute to the understanding of their role for bacterial proliferation in the rhizosphere. Show less
