TheppuI-rsaL-ppuRQuorum-Sensing System Regulates Biofilm Formation ofPseudomonas putidaPCL1445 by Controlling Biosynthesis of the Cyclic Lipopeptides Putisolvins I and II

Abstract
Pseudomonas putidastrain PCL1445 produces two cyclic lipopeptides, putisolvin I and putisolvin II, which possess surface tension-reducing abilities and are able to inhibit biofilm formation and to break down existing biofilms of severalPseudomonasspp., includingP. aeruginosa. Putisolvins are secreted in the culture medium during growth at late exponential phase, indicating that production is possibly regulated by quorum sensing. In the present study, we identified a quorum-sensing system in PCL1445 that is composed ofppuI,rsaL, andppuRand shows very high similarity with gene clusters ofP. putidastrains IsoF and WCS358. Strains with mutations inppuIandppuRshowed a severe reduction of putisolvin production. Expression analysis of the putisolvin biosynthetic gene in appuIbackground showed decreased expression, which could be complemented by the addition of synthetic 3-oxo-C10-N-acyl homoserine lactone (3-oxo-C10-AHL) or 3-oxo-C12-AHL to the medium. AnrsaLmutant overproduces AHLs, and production of putisolvins is induced early during growth. Analysis of biofilm formation on polyvinylchloride showed thatppuIandppuRmutants produce a denser biofilm than PCL1445, which correlates with decreased production of putisolvins, whereas anrsaLmutant shows a delay in biofilm production, which correlates with early production of putisolvins. The results demonstrate that quorum-sensing signals induce the production of cyclic lipopeptides putisolvin I and II and consequently control biofilm formation byPseudomonas putida.

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