Copper sulfate inhibition of quorum sensing in Pseudomonas capeferrum is dependent on biotic interactions

Quorum Sensing (QS) signaling, which allows the coordination of the microbial physiology, can be influenced by environmental factors. However, the impact of copper-based fungicides on the QS of rhizosphere microorganisms is currently unknown. The simultaneous presence of other microorganisms may also alter the QS signaling. In this work we report that the fungicide CuSO4 modifies the expression from the promoter of ppuI, ppoR and rsaL, components of Pseudomonas capeferrum WCS358 QS system. ppuI and ppoR promoters showed a biphasic behavior reducing their activities as CuSO4 concentrations increased up to 1 mmol l(-1), but with increased values at higher metal concentrations. rsaL promoter attained a minimal activity with 1 mmol l(-1), though higher concentrations did not modify its expression. The impact of CuSO4 on biofilm formation by WCS358 was dependent on the bacterial QS activity. Dual biofilms with Papiliotrema laurentii YL2 yeast were also affected by the bacterial QS and the metal. CuSO4 was detrimental for the bacterial colonization, but YL2 exerted a protective effect in dual colonies, an effect that depended on the QS activity. These results suggest the importance of the WCS358 QS systems in the rhizosphere, where copper-based fungicides and concomitant microorganisms conform a complex system.