Dinâmica e diversidade das comunidades microbianas em cavernas tropicais do Brasil Central

Abstract

Subterranean environments are generally considered extreme oligotrophic and have specific characteristics that determine the local microbiota, such as: different humidity conditions, temperature and nature of nutritional resources. Although studies on environmental microbial diversity have made considerable advances, few researches have investigated the terrestrial microbiota of subterranean environments, mainly in tropical regions. Considering that the diversity and dynamics of the microorganisms of these environments is practically unexplored, this study had as aim to analyze, firstly, the current scenario of conservationist policies in Brazilian caves and to discuss the trophic level in tropical and temperate caves. In addition, in order to characterize microbial communities in tropical caves, the composition and structure of microbial biodiversity (bacteria and fungi) and environmental conditions (physicochemical parameters) were evaluated in all samples sampled in three caves of a Brazilian Conservation Unit (State of Terra Ronca - PETER, São Domingos, GO). Brazilian legislation was consulted on the use and conservation of caves, concentrations of organic carbon and total nitrogen were measured in tropical caves, as well as microbial attributes (biomass and respiration) to understand the dynamics of the microbial community in relation to the availability of organic matter. Composition and structure of microbial communities along a trophic gradient (surface > cave entrance > subterranean) was evaluated in each cave studied. We used the sequencing of 16S and ITS (rRNA) genes to access the biodiversity of fungi and bacteria. The use of microbial studies in the conservation policies of cave dwellers environments was discussed from the data obtained in this research. Considering published and new data on the quantity and quality of dissolved organic matter (carbon and nitrogen) in tropical and temperate caves, much care is needed when considering all the subterranean environments as extreme oligotrophic. Actinobacteria and Proteobacteria (mainly Alpha and Gamma) were the most frequent bacterial groups in the caves studied. Among the fungi, large proportions of Actinomycetes were observed in subterranean environments, mainly in dry period. Although most microbial communities are characterized by detritivorous microorganisms, some microorganisms known for chemoautotrophic activity (such as Beggiatoa) were observed in this study. The large number of uncultured bacteria and unidentified fungi in tropical caves is remarkable, indicating the great potential of this habitat to house new species of microorganisms. Structure and composition of the microbial communities in the studied caves were more dissimilar among them in subterranean environments than in surface environments. This dissimilarity among the microbial communities confers a singularity to each cave studied. Finally, microbial community in one of the studied caves showed evidence of the Halobacteriacea family dominance in entrance cave, probably due to its environmental conditions, such as high salinity of the substrate. The data obtained in this study enrich the knowledge of microbial biodiversity, clarify knowledge about the structure and dynamics of microbial communities in tropical caves and contribute to future proposals for cave environments conservation.