Composição da comunidade de cianobactérias e outros grupos microbianos em dois reservatórios tropicais

Abstract

The diversity of phytoplankton in aquatic environments is an important indicator of water quality and of ecological relationships established in environment. The accurate assay of this diversity is of great importance in ecological studies as well as in any recovery action, when needed. Within the phytoplankton, the group of cyanobacteria has received special attention due to the ability of these organisms to grow and dominate in eutrophic freshwater ecosystems, as well as the potential toxicity of some species that may hinder or even prevent the use of water for recreational and drinking purposes. For several years the cyanobacteria diversity in aquatic environments has been assessed primarily using traditional taxonomic methods, which are based on morphological characteristics. However because of the large morphological variability of the colonies, it can be difficult to define the boundaries between species, hampering the use these methods. Thus, the use of molecular techniques has increased to assist in the identification of cyanobacteria, as well as other microbial groups, contributing to the characterization of microbial communities in aquatic environments, maximizing the information needed for the description of the environment. In this study we evaluated the composition of the cyanobacteria community and its seasonal and spatial changes in two reservoirs located in Minas Gerais (Pampulha and Volta Grande), in addition to a preliminary study on the presence of other bacteria and arquea in these same environments and on the possible association between cyanobacteria and these two microbial groups. Pampulha reservoir is located in Belo Horizonte city, Minas Gerais. The main problem of this reservoir is the continuous input of domestic and industrial sewage, which increases the supply of nutrients with the consequent increase in eutrophication and cyanobacterial blooms. Volta Grande Reservoir is located in the Rio Grande river, between the states of Minas Gerais and São Paulo. Due to its low retention time and high dilution rate, Volta Grande can still be characterized as an oligotrophic reservoir (Greco 2002). In this study, the identification and enumeration of cyanonacteria species was made by traditional microscopy (Utermöhll 1958), associated with the molecular technique PCR-DGGE (Denaturating Gradient Gel Electrophoresis) (Muyzer et al. 1993). The results showed that these techniques are complementary and help giving a more complete picture of the cyanobacteria community composition in both environments. Using specific primers, the same molecular technique was used for the study of microorganisms from the Bacteria and Archaea groups. The results showed: a) high dominance of cyanobacteria during the whole study period in Pampulha reservoir; b) presence of cyanobacteria, mainly belonging to picocyanobacteria, in Volta Grande reservoir; c) high diversity of organisms of the Domain Archaea, more specifically the group of methanogenic archaea, in samples of both reservoirs and in cyanobacterial cultures.