Abstract
The Archaea domain is ubiquitously distributed and extremely diverse, however, environmental factors that shape archaeal community structure are not well known. Aquatic environments, including the water column and sediments harbor many new uncultured archaeal species from which metabolic and ecological roles remain elusive. Some environments are especially neglected in terms of archaeal diversity, as is the case of pristine tropical areas. Here we investigate the archaeal composition in marine and freshwater systems from Ilha Grande, a South Atlantic tropical environment. All sampled habitats showed high archaeal diversity. No OTUs were shared between freshwater, marine and mangrove sediment samples, yet these environments are interconnected and geographically close, indicating environment-specific community structuring. Group II Euryarchaeota was the main clade in marine samples, while the new putative phylum Thaumarchaeota and LDS/RCV Euryarchaeota dominated freshwaters. Group III Euryarchaeota , a rare clade, was also retrieved in reasonable abundance in marine samples. The archaeal community from mangrove sediments was composed mainly by members of mesophilic Crenarchaeota and by a distinct clade forming a sister-group to Crenarchaeota and Thaumarchaeota. Our results show strong environment-specific community structuring in tropical aquatic Archaea, as previously seen for Bacteria.
Highlights
It is well established that Archaea are widely distributed and numerically significant in aquatic ecosystems [1,2,3,4]
Since molecular methods started to be applied to the study of uncultivated microbial communities [5], knowledge of their ecology in aquatic systems has been significantly increased [6,7,8,9] but archaeal diversity and distribution remain poorly known
Isolation and complete genome sequencing of members of this group, as Nitrosopumilus maritimus from marine aquarium sediment [17,18] and Cenarchaeum symbiosum from a marine sponge [19,20], shed light on its ecology and deep phylogenetic study of this group strongly suggests that Group I Archaea form an exclusive division within the Archaea domain, the Thaumarchaeota [21,22,23]
Summary
It is well established that Archaea are widely distributed and numerically significant in aquatic ecosystems [1,2,3,4]. Since molecular methods started to be applied to the study of uncultivated microbial communities [5], knowledge of their ecology in aquatic systems has been significantly increased [6,7,8,9] but archaeal diversity and distribution remain poorly known. Marine environments are the most thoroughly studied among aquatic ecosystems concerning archaeal diversity. Group II Euryarchaeota are common in euphotic zones of open ocean waters and in shallow coastal zones [10,11,12] while rare taxa like Groups III and IV Euryarchaeota [13,14] can occur in deep ocean waters. Isolation and complete genome sequencing of members of this group, as Nitrosopumilus maritimus from marine aquarium sediment [17,18] and Cenarchaeum symbiosum from a marine sponge [19,20], shed light on its ecology and deep phylogenetic study of this group strongly suggests that Group I Archaea form an exclusive division within the Archaea domain, the Thaumarchaeota [21,22,23]
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