The Institute of Aerospace medicine was now involved in a study to find out more on the bacterial diversity in caves: In the Su Bentu limestone cave in Sardinia, Italy, the influence of human exploration on the microbial community structure and ammonia oxidizing potential was investigated. It served to deepen the understanding of the microbial interactions within subterranean environments and to elucidate the microbial diversity as well as the impact of human exploration on the native system of the Su Bentu Cave.
Due to their subsurface nature and to the lack of sunlight, caves are nutrient depleted environments where the levels of available organic carbon to support heterotrophic microbial growth are significantly lower than in terrestrial surface ecosystems. As such, in underground systems the metabolic potential and flexibility of microbial communities in a habitat with potential similarities to diverse globally dominant terrestrial and marine environments can be analyzed. The Su Bentu cave comprises over 15 km explored passages and most of the cave is not subjected to flooding, creating a typical oligotrophic environment. For six days, six “caveonauts” investigated the cave and took samples from speleothems (calcite rafts, manganese oxide deposits etc.) deep inside the cave to investigate the microbiome of this extreme environment. Altogether, the cavenauts returned with 7 different samples, allowing the scientists to analyze the microbiome in great detail. Together with the University of Graz and the EU program EUROPLANET, the scientists from the DLR Institute of Aerospace Medicine analyzed the samples.
Within the cave, one spot is regularly used as campsite which serves as a test-bed to investigate the human impact of short-term settlement on the present microbial diversity. The microbial community there is predominately composed of the phyla Proteobacteria, Actinobacteria, Acidobacteria, Nitrospirae, and Firmicutes. Sampling sites near the entrance of the cave and in close proximity of the underground campsite revealed the highest diversity as well as the highest number of human associated microorganisms. Two samples obtained in very close proximity of each other near the campsite indicate that the human impact is localized and is not distributed freely within the system. Also, the samples showed that microorganisms inhabit a diverse number of extreme environments such as hot springs, glacial lakes and subterranean systems.
The results of this study show that human impact is confined to locations that are utilized as campsites and that exploration leaves little microbial trails. Furthermore, the scientists uncovered a highly specialized microbiome which is perfectly adapted to survive and thrive in an environment with low nutrient availability.
The study was now published in the journal PLoS ONE:
Leuko S, Koskinen K, Sanna L, D'Angeli IM, De Waele J, Marcia P, et al. (2017) The influence of human exploration on the microbial community structure and ammonia oxidizing potential of the Su Bentu limestone cave in Sardinia, Italy. PLoS ONE 12(7): e0180700. https://doi.org/10.1371/journal.pone.0180700