Tropical aquatic Archaea show environment-specific community composition.

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.

Microbial community compositional shifts in bleached colonies of the Brazilian reef-building coral Siderastrea stellata.

The association of metazoan, protist, and microbial communities with Scleractinian corals forms the basis of the coral holobiont. Coral bleaching events have been occurring around the world, introducing changes in the delicate balance of the holobiont symbiotic interactions. In this study, Archaea, bacteria, and eukaryotic phototrophic plastids of bleached colonies of the Brazilian coral Siderastrea stellata were analyzed for the first time, using 16S rRNA gene libraries. Prokaryotic communities were slightly more diverse in healthy than in bleached corals. However, the eukaryotic phototrophic plastids community was more diverse in bleached corals. Archaea phylogenetic analyses revealed a high percentage of Crenarchaeota sequences, mainly related to Nitrosopumilus maritimus and Cenarchaeum symbiosum. Dramatic changes in bacterial community composition were observed in this bleaching episode. The dominant bacterial group was Alphaproteobacteria followed by Gammaproteobacteria in bleached and Betaproteobacteria in healthy samples. Plastid operational taxonomic units (OTUs) from both coral samples were mainly related to red algae chloroplasts (Florideophycea), but we also observed some OTUs related to green algae chloroplasts (Chlorophyta). There seems to be a strong relationship between the Bacillariophyta phylum and our bleached coral samples as clones related to members of the diatom genera Amphora and Nitzschia were detected. The present study reveals information from a poorly investigated coral species and improves the knowledge of coral microbial community shifts that could occur during bleaching episodes.

Pollution impacts on bacterioplankton diversity in a tropical urban coastal lagoon system.

Despite a great number of published studies addressing estuarine, freshwater and marine bacterial diversity, few have examined urban coastal lagoons in tropical habitats. There is an increasing interest in monitoring opportunistic pathogens as well as indigenous microbial community members in these water bodies by current molecular and microbiological approaches. In this work, bacterial isolates were obtained through selective plate dilution methods to evaluate antibiotic resistances. In addition, 16S rRNA gene libraries were prepared from environmental waters and mixed cultures grown in BHI medium inoculated with Jacarepaguá lagoon waters. Denaturing gradient gel electrophoresis (DGGE) analyses showed distinct community profiles between environmental communities from each studied site and their cultured counterparts. A total of 497 bacterial sequences were analyzed by MOTHUR, yielding 245 operational taxonomic units (OTUs) grouped at 97% similarity. CCA diagrams showcased how several environmental variables affect the distribution of 18 bacterial orders throughout the three distinct habitats. UniFrac metrics and Venn diagrams revealed that bacterial communities retrieved through each experimental approach were significantly different and that only one OTU, closely related to Vibrio cholerae, was shared between them. Potentially pathogenic bacteria were isolated from most sampled environments, fifty percent of which showed antibiotic resistance.

Gut bacterial communities in the giant land snail Achatina fulica and their modification by sugarcane-based diet.

The invasive land snail Achatina fulica is one of the most damaging agricultural pests worldwide representing a potentially serious threat to natural ecosystems and human health. This species is known to carry parasites and harbors a dense and metabolically active microbial community; however, little is known about its diversity and composition. Here, we assessed for the first time the complexity of bacterial communities occurring in the digestive tracts of field-collected snails (FC) by using culture-independent molecular analysis. Crop and intestinal bacteria in FC were then compared to those from groups of snails that were reared in the laboratory (RL) on a sugarcane-based diet. Most of the sequences recovered were novel and related to those reported for herbivorous gut. Changes in the relative abundance of Bacteroidetes and Firmicutes were observed when the snails were fed a high-sugar diet, suggesting that the snail gut microbiota can influence the energy balance equation. Furthermore, this study represents a first step in gaining a better understanding of land snail gut microbiota and shows that this is a complex holobiont system containing diverse, abundant and active microbial communities.