A lectin-based approach for visualization of capsular EPS after attachment and biofilm formation by acidophilic leaching bacteria

摘要

Bioleaching is the dissolution of metal sulfides, such as pyrite ( FeS2) , by bacterial-driven oxidation processes. Selective attachment and biofilm formation on sulfidic mineral surfaces by Acidithiobacillus ferrooxidans and other leaching microorganisms is a crucial step for bioleaching. Uronic acid residues present in the extracellular polymeric substances (EPS) bind ferric ions, which are the main oxidative agents involved in pyrite dissolution, contributing to establish a reaction space in the EPS-matrix, helping to the connection of the bacterial respiratory chains with the chemical oxidation of pyrite. EPS composition of ferrous iron and pyrite grown cells is similar, but more EPS are produced when cells are grown on solid substrates. In this work we have studied capsular polysaccharide (CPS) production in Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum by epifluorescence and confocal laser microscopy (CSLM) , using TRIT-C labeled lectin Concanavalin A (ConA). Cells were imaged after growth on floating filters and after exposure to pyrite. Under these growth conditions, attached and planktonic cells showed a stronger ConA signal compared with iron-grown cells. This study will contribute to elucidate the still unknown factors that trigger EPS biosynthesis after contact with sulfidic minerals and the influence of external factors on this process, being also fundamental for further molecular analyses in order to determine the induction of possible EPS biosynthesis pathways and other factors involved in the process of biofilm formation by leaching bacteria on metal sulfides.