INVESTIGATION OF NITROGEN CYCLING AND NOVEL MICROBIAL DIVERSITY IN LAVA TUBES OF TERCEIRA, AZORES, PORTUGAL

The subterranean world of caves supports a diverse community of organisms, despite the lack of solar radiation and often low availability of nutrients. Lava tubes are common in volcanic terrains worldwide, yet are understudied compared to their more famous limestone cave counterparts. They also make an excellent analog for studying the subsurface environments of other planets. The walls and ceiling of lava tubes are often covered in colorful microbial mats, and other microbial deposits, some of which look very mineralogical in nature. However, little is known about which organisms are present and what ecological roles they fulfill. One such ecological role could be cycling nitrogen within the cave systems. The oxidation and reduction of nitrogen provides energy and bioavailable N for many types of microorganisms. Studies of the organisms responsible for N transformation in soil and aquatic habitats continue to yield new discoveries. These analyses have not been conducted in subterranean habitats where N limitation is a major constraint on biological production. Understanding how the bacteria in lava tubes are able to obtain this scarce, critical element from a nitrogen-poor environment would provide greater insight into the ecological dynamics of lava tubes, and provide a basis for comparison to lava tubes on Mars. Nitrogen is the second most abundant element in the Martian atmosphere, and studies continue to search for different forms of nitrogen on Mars. Molecular methods were used to determine the diversity of species present in Azorean lava tubes, and to determine if these bacteria are capable of participating in nitrogen cycling. Fourteen phyla have been identified from the lava tubes, including Nitrospira. Ammonia oxidation is suggested to occur in six of the 11 caves studied, based on the presence of the amoA gene in extracted genomic DNA. Nitrogen fixation is also suggested to occur nine of the 11 caves, based on the presences of the nifH gene. These results support our hypothesis that nitrogen cycling by microorganisms occurs in the lava tube ecosystem.