Early steps in microbial colonization processes at deep‐sea hydrothermal vents

<jats:title>Summary</jats:title> <jats:p> A pluri‐disciplinary <jats:italic>in situ</jats:italic> colonization experiment was performed to study early stages of colonization in deep‐sea vent <jats:italic>Alvinella</jats:italic> spp. worm habitats. Four colonization devices were deployed onto <jats:italic>Alvinella</jats:italic> spp. colonies of different chimneys of the East‐Pacific Rise (EPR 13°N), for two different periods: a short (less than a week) and a longer one (3 weeks). Video imagery and monitoring of the thermal and physico‐chemical conditions were performed during the colonization experiments. Numerous microorganisms bearing specialized adhesion‐appendages and/or high amounts of polymeric extracellular matrix were observed on devices, which may efficiently contribute to the colonization of new surfaces. The microbial cohorts preceding and accompanying <jats:italic>Alvinella</jats:italic> spp. settlement were identified. In all cases, <jats:italic>Archaea</jats:italic> could not be detected and the microbial mats were essentially composed of e‐ <jats:italic>Proteobacteria</jats:italic> . Within this group, one phylotype ( <jats:italic>Alvi</jats:italic> H2) was found to dominate the libraries of three colonization devices. Dominance of e‐ <jats:italic>Proteobacteria</jats:italic> in the libraries may reflect the wide physiological variety encountered within this group or an adaptability of these microorganisms towards their changing environment. Bacteria affiliated to the <jats:italic>Cytophaga‐Flavobacterium‐Bacteroides</jats:italic> group or to the e‐ <jats:italic>Proteobacteria</jats:italic> , that grow either chemo‐organoheterotrophically by fermentation or chemolithoautotrophically with H <jats:sub>2</jats:sub> as an electron donor and S°/S <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> <jats:sup>2–</jats:sup> or NO <jats:sub>3</jats:sub> <jats:sup>–</jats:sup> as a terminal electron acceptor, were isolated from one of the microbial mat formed in 20 days. </jats:p>