Is the Quorum Sensing Type AI-1 System of <i>Acidithiobacillus ferrooxidans</i> Involved in its Attachment to Mineral Surfaces?

Abstract

Biofilm development plays a pivotal role in the bioleaching process. The attachment of the acidophilic chemolithotrophic Acidithiobacillus ferrooxidans to mineral surfaces is mediated by extracellular polymeric substances (EPS) involved in biofilm development. Previous work suggests that EPS composition of A. ferrooxidans is adapted to the energy source and, accordingly, the bacterium must be able to sense the surface to which attachment occurs with the consequent triggering of the expression of different EPS-genes. Quorum sensing (QS) is recognized as one of the main regulators of biofilm formation. A. ferrooxidans possesses a functional QS type AI-1 system and the analysis of culture supernatants revealed us that this bacterium is able to synthesize nine different homoserine lactones (AHLs) whose acyl-chain lengths oscillate between 8 and 16 carbons and include an alcohol or a ketone function at the C3 position. The transcription levels of the afeI gene encoding for the AHL synthase are higher in cells grown in sulfur and thiosulfate media than in iron-grown cells, suggesting that biofilm formation in A. ferrooxidans would be regulated by the QS type AI-1 system. In the present study, the effect of several synthetic AHLs and analogues on the attachment of A. ferrooxidans to pyrite was analyzed. Preliminary results suggest that some of these molecules are changing the bacterial attachment to pyrite.