Eco-physiological, chemotactic and taxonomic characterization of hypersaline Beggiatoa originating from microbial mats

Abstract

In this thesis, hypersaline Beggiatoa spp. were characterized with respect to their physiology (function) and their phylogeny (structure) in their natural habitat (In situ) - phototrophic microbial mats from various origins (Spain, Mexico) - and in laboratory set-ups (Ex situ). Nitrate storage enables Beggiatoa to oxidize sulfide anaerobically during darkness. Chemotactic experiments determined the triggers, which influence the distributions pattern of Beggiatoa in their natural habitat. Nitrate appeared to attract, while oxygen and blue light repelled filaments. Sulfide was the key trigger determining motility, attracting filaments at low, but repelling them at high sulfide concentrations. The gliding locomotion mechanism by slime jets excretion could be visualized by lectin-staining and confocal laser microscopy. A new genus name was proposed for the group of hypersaline Beggiatoa: 'Candidatus Halobeggiatoa', which showed closest affiliations to marine strains isolated from saltmarshes. A new method to display low pH (2-5) in vacuoles of live Beggiatoa was developed based on excited state saturation of fluorescein isothiocyanate.