Microbial diversity in wetlands of Sisal, Yucatan, Mexico

Tropical wetlands are globally important ecosystems found in regions with high humidity, rainfall and decaying organic matter. They are one of the largest carbon reservoirs in the planet. These sites are characterized by low pH, high saline concentrations and a low quantity of nutrients. We evaluated the microbial diversity from the wetlands of Sisal, Yucatan Mexico using a metagenomic approach. To this end, five points were scrutinized and water was collected monthly for a period of one year (2014). The water was filtered (0.25 micron filter) and metagenomic DNA obtained (Rojas et al., 2008). From this, 2 μg of DNA where sequenced by Ilumina. Sequences were assembled by using Velvet, then their corresponding contigs were analyzed with the metaserver MG-RAST.

In total, 14,399,561 sequences were analyzed, from which 92% corresponds to Bacteria, 0.7% to Archaea, 6.2% to Eukaryota, and 0.54% to Viruses. The Bacteria kingdon was the most abundant, with Proteobacteria, Bacteroidetes, Actinobacteria, Cyanobacteria and Firmicutes the most abundant. Previous reports have found a similar bacterial composition in different wetlands and swamps; the differential abundance at Phylum could be due the characterisitcs of the Sisal wetlands. The presence of Proteobacteria, Bacteroidetes, Actinobacteria and Cyanobacteria are common in tropical marshes and mangroves, these communities are considered cosmopolitans. The afore mentioned Phyla are found in water bodies with decaying organic matter and are considered the most metabolic active. In the Sisal wetlands the functional analysis of the sequenced community showed a high representation of metabolism, genetic and environmental information processing. The carbohydrate metabolism was among the most represented subsystems due presence of decaying organic matter and the action of several enzymes (cellulose, xylanose). The presence of Cyanobacteria in the carbohydrate metabolism subsystem is important due to biofilm-producing ability of these phylum, this biofilm provides structural and physiological support which allows the interaction with other organisms. The cyanobacterial communities exerts an ecological role by the growth-inhibition of other organisms (fungi, algae, insects) due to bioactive peptides found in the genus Anabaena, Fischerella and Nostoc. The Euryarcheota represented 90% of the Archea, these organisms are involved in methanogenic and other geochemical processes in marshes, swamps and wetlands. We found members of the genus Methanosarcina and Methanobacterium. Low-represented metabolic subsystems related to to N, S and P metabolism were found. The low abundance of these elements was reported in marshes and similar water bodies in accordance with the low abundance of phyla associated with the mineralization of these elements. Other subsystems such as stress reponse, mobile elements, defense genes and pathogenesis were found in the Sisal marsh, which are involved in the response of the microbial community to enviromental changes.

In summary, the microbial and metabolical diversity identified in the Sisal wetlands reflects a complex and dynamical environment, suggesting that organisms are adapting to all extreme changes, such as salinity, temperature, and pH, throughout all the seasons. In addition, some microorganisms are indicators that show the presence of metals to Betaproteobacteria (Thiobacillus and Thiomonas) and in Deltaproteobacteria (Anaeromyxobacter and Geobacter) Table 1, a large accumulation of organic matter and aerobic-anaerobic changes. The information provided here contributes significantly not only to the understanding of the microbial diversity and dynamics in this ecological niche, but open the opportunity to explore organisms with biotechnology applications.