Biofilm formation and extracellular polymeric substances of acidophilic metal/sulfur-oxidizing archaea
In this study, biofilm formation and extracellular polymeric substances (EPS) of acidophilic archaea were investigated. Three representative archaeal species extremely acidophilic archaeon Ferroplasma acidiphilum, thermoacidophilic archaea Acidianus sp. DSM 29099 and Sulfolobus metallicus were chosen as test organisms. Several cultivation and advanced microscopical techniques e.g. CLSM, AFM & EFM and SEM were used to visualize and characterize biofilm development and EPS of acidophilic archaea. In addition, FLBA, ATR-FTIR and conventional spectroscopic methods were applied for qualification and quantification of EPS components. F. acidiphilum biofilms were heterogeneously distributed on polycarbonate filters over time, and varied within the different growth conditions such as supplementation with glucose. Cells formed a monolayer biofilm and were preferably attached to the defect sites of pyrite surfaces. Biofilm and planktonic cells exhibited significant morphological differences as revealed by AFM. Low coverage of pyrite surface by cells seems to correlate with their low leaching ability. Screening of a lectin library resulted in the detection of 21 lectins able to bind archaeal biofilms on pyrite and to Acidianus sp. DSM 29099 biofilms on elemental sulfur (S0). These lectins can be used in studies for assessment of interactions between various members of microbial bioleaching communities, especially in order to elucidate the role of archaea in detail. The major binding patterns, e.g. tightly bound EPS and loosely bound EPS, were detected on both substrates pyrite and S¬0. The three archaeal species produced various EPS glycoconjugates containing sugar moieties like glucose, galactose, mannose, GlcNAc, GalNAc, sialic acid, and fucose. Additionally, the substratum induced different EPS glycoconjugates and biofilm structures for cells of Acidianus sp. DSM 29099. EPS analysis of S. metallicusT on S0 showed that capsular EPS from planktonic cells were mainly composed of carbohydrates and proteins. In contrast, colloidal EPS from planktonic cells were dominated by carbohydrates. Proteins were found to be major components in EPS from biofilms on S0. In addition, extracellular proteins and nucleic acids were present in the EPS matrix. The existence of these compounds suggest their potential roles in biofilm formation and stabilization. S. metallicusT cells were shown to be embedded in a gel-like and flexible EPS matrix, where cells were often found to be motile (back and forth) either self-propelled by cellular appendages or by ‘Brownian motion’.
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