Estrutura da comunidade microbiana associada a sedimentos de água doce

Abstract

Bacterial communities play an important role in the mineralization of organic matter and in the biogeochemical cycles of ecosystems. Sediments from aquatic ecosystems can contain thousands of species of bacteria in high abundance. Even with all this diversity and abundance, there is still a huge knowledge gap about how these microorganisms live and the functions they play in these ecosystems. This work aimed to evaluate the structure of the microbial community (i.e. total abundance and selected functional groups) in sediment profiles from three environments: river, transition and dam of the Funil Hydroelectric Reservoir, in the Paraíba do Sul River basin. The sediment sampling was carried out in July 2018 by performing transects in the three environments, totaling five cores per transect. In the laboratory, the sediment cores were fractionated every 2 cm to 10 cm in depth for the analysis of Organic Matter (OM), Total Nitrogen (TN), Total Phosphorus (TP), TN: TP ratio and microbial composition (total community, archaea, methanogenic, sulfate-reducing and proteobacteria). The microbial communities were evaluated for the total density of individuals and functional composition according to the fluorescent in situ hybridization (FISH) technique. The OM showed higher concentrations in the dam transect. TN showed a higher concentration in the dam at depth 6 cm along the profile (1,526.95 µg / g). TP showed a higher concentration in the transition environment (222.74 µg / g). The TN:TP molar ratio was higher in the dam. Methanogenic archeas represented 7.3 % of the total average density in the river environment, 5.9 % in the transition and 12.4 % in the dam. Methanosarcina spp. represented 6.8 % of the total average density in the river and transition environments and 14.8 % in the dam. Desulfovibrionales represented 6.3 % of the total average density in river environments, 9.7 % in the transition and 14.8 % in the dam. Proteobacteria (delta, epsilon, beta and gamma) represented 26.8 % of the total average density in river environments, 25.9 % in the transition and 39.0 % in the dam. In general, the dam was the environment that showed the highest total and group density, as well as the greatest relative contribution of the microbial groups evaluated in relation to the river and transition environments. Throughout the sediment profiles, no significant patterns of concentrations of OM, TP, TP, as well as TN: TP ratio and microbial community were found. Understanding how these communities are structured in freshwater sediments can contribute to a better understanding of their dynamics and ecosystem functions in order to support future studies and predict how these ecosystems will change as a result of anthropogenic activities.