Microbial life in Brazilian caves: reporting the structure of bacterial communities

Few studies have used next generation sequencing to assess the microbial diversity in tropical caves. In order to better understand microbial structure in tropical caves, DNA was extracted from soil and sediment samples in four tropical subterranean systems located in Terra Ronca State Park, Central of Brazil: Angélica cave, São Bernardo cave, Terra Ronca I and Terra Ronca II caves. After DNA extraction, the V3-V4 regions (16S) were amplified and the sequences were used for the analysis. Environmental variables (such as temperature, air and substrate humidity, pH, organic carbon and total nitrogen) related to microbial communities were analysed. The bacterial communities showed dominance of Actinobacteria (38.52%) and Proteobacteria (mainly Alphaprotebacteria (10.41%) and Gammaproteobacteria (8.98%)) in subterranean samples. Bacterial communities showed 52.82% OTUs from uncultivable organisms. High proportion of bacterial OTUs with saprophytic function indicates the importance of the detritivorous food chain in those tropical caves. The strong correlation between the structure of the microbial communities and the amount of organic carbon supports this statement. Bacterias of the family Nitrosomonadaceae and genus Nitrospira were found in all collected samples, which are microorganisms indicating oxidizing activities of ammonia and nitrite coupled to CO2 fixation in subterranean environments. Cave entrance of Terra Ronca II stood out with high dominance of Halobacteria (more than 60.0 % of the bacterial community), a group of Archaea. This is the first evidence of Halobacteriaceae dominance in a cave, microorganisms known for chemoautotrophic activity and nitrate reduction. Microbial life inside caves showed greater dissimilarity between communities than in surface environments. There was a clear distinction between the habitats studied in the ordination analyses, especially when only microorganisms with abundance less than 0.01% (rare biosphere) were considered. This study showed that although microbial communities in tropical caves have similar composition (filos and classes), as caves around the world, subterranean communities have specific microorganisms (genus and species), many of which are unknown, present in those habitats. The uniqueness of the microorganism species presents in each cave and the strong relationship with the input of allochthonous nutrients make microbial studies in tropical caves a priority tool to evaluate the use and management of these environments. Increased efforts to study diversity and microbial communities dynamics allow the knowledge of new species of microorganisms, relationships of microbial communities with the ecological dynamics in subterranean habitats and possible risks in the exploitation of that environment.

Authors: Caio César Pires de Paula 1, Maria Elina Bichuette2, Mirna Helena Regali Seleghim2

1 – Institute of Hydrobiology (HBÚ), Biology Centre CAS, České Budějovice, Czech Republic.

2 – Federal University of São Carlos, São Carlos – SP, Brazil.

Section: Cave Biology / Bio speleology

Type: Oral presentation

Short bio of the presenter: Caio César Pires de Paula is a biologist and and started cave studies in the Federal University of São Carlos, Brazil. Nowaday he work in Biology Centre CAS, at the Institute of Hydrobiology, Czech Republic. The researcher worked in tropical caves seeking to understand nutrient flow and microbial dynamics. Your focus of study is fungi and bacteria communities in several ecosystems, with special attention to caves. Research results can to corroborate with the knowledge of microbial biodiversity and to discuss the functional role of the microbial communities in the dynamics of natural environments. In subterranean environments, the researcher intends to promote the discussion about the functional role and the dynamics of microorganisms. Finally, the researcher have experience in biotechnological processes, looking for new potentially valuable microorganisms, such as higher yields enzyme producers, isolated from the subterranean environment.

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