Abstract:
Hypoliths (cryptic microbial assemblages that develop on the undersides of translucent rocks) are significant
contributors to regional C and N budgets in both hot and cold deserts. Previous studies in the Dry Valleys of
Eastern Antarctica have reported three morphologically distinct hypolithic community types: cyanobacteria
dominated (type I), fungus dominated (type II) and moss dominated (type III). Here we present terminal-restriction
fragment length polymorphism analyses to elucidate the bacterial community structure in hypolithons and the
surrounding soils. We show clear and robust distinction in bacterial composition between bulk surface soils and
hypolithons. Moreover, the bacterial assemblages were similar in types II and III hypolithons and clearly
distinct from those found in type I. Through 16S rRNA gene 454 pyrosequencing, we show that Proteobacteria
dominated all three types of hypolithic communities. As expected, Cyanobacteria were more abundant in
type I hypolithons, whereas Actinobacteria were relatively more abundant in types II and III hypolithons, and were
the dominant group in soils. Using a probabilistic dissimilarity metric and random sampling, we demonstrate that
deterministic processes are more important in shaping the structure of the bacterial community found in types II
and III hypolithons. Most notably, the data presented in this study suggest that hypolithic bacterial communities
establish via a successional model, with the type I hypolithons acting as the basal development state.
