Abstract
BackgroundBasalt is the most common igneous rock on the Earth’s surface covering. Basalt-associated microorganisms drive the cycling and sequestration of different elements such as nitrogen, carbon and other nutrients, which facilitate subsequent pioneer and plant development, impacting long-term regulation of the Earth’s temperature and biosphere. The initial processes of colonization and subsequent rock weathering by microbial communities are still poorly understood and relatively few data are available on the diversity and richness of the communities inhabiting successive and chronological lava flows. In this study, the bacterial communities present on lava deposits from different eruptions of the 1975–84 Krafla Fires (32-, 35- and 39-year old, respectively) at the Krafla, Iceland, were determined.ResultsThree sites were sampled for each deposit (32-, 35- and 39-year old), two proximal sites (at 10 m distance) and one more distant site (at 100 m from the two other sites). The determined chemical composition and metal concentrations were similar for the three basalt deposits. No significant differences were observed in the total number of cells in each flow. 16S rRNA gene amplicon sequencing showed that the most abundant classified phylum across the 3 flows was Proteobacteria, although predominance of Acidobacteria, Actinobacteria and Firmicutes was observed for some sampling sites. In addition, a considerable fraction of the operational taxonomic units remained unclassified. Alpha diversity (Shannon, inverse Simpson and Chao), HOMOVA and AMOVA only showed a significant difference for Shannon between the 32- and 39-year old flow (p < 0.05). Nonmetric multidimensional scaling (NMDS) analysis showed that age significantly (p = 0.026) influenced the leftward movement along NMDS axis 1.ConclusionsAlthough NMDS indicated that the (relatively small) age difference of the deposits appeared to impact the bacterial community, this analysis was not consistent with AMOVA and HOMOVA, indicating no significant difference in community structure. The combined results drive us to conclude that the (relatively small) age differences of the deposits do not appear to be the main factor shaping the microbial communities. Probably other factors such as spatial heterogeneity, associated carbon content, exogenous rain precipitations and wind also affect the diversity and dynamics.
Highlights
Basalt is the most common igneous rock on the Earth’s surface covering
Since solidified lava cannot retain much water, early microbial colonization depends on precipitation and an exogenous source of nutrients, e.g. atmospheric trace gasses that could serve as a source of carbon and energy [7, 8]
The total number of cells determined by flow cytometry showed that the three sampling sites within the three flows contained between 6.80 × and 7.54 × cells/g (Fig. 2)
Summary
Basalt-associated microorganisms drive the cycling and sequestration of different elements such as nitrogen, carbon and other nutrients, which facilitate subsequent pioneer and plant development, impacting long-term regulation of the Earth’s temperature and biosphere. Microorganisms drive the cycling and sequestration of different elements such as nitrogen, carbon and other nutrients, which facilitate subsequent pioneer and plant development, impacting long-term regulation of the Earth’s temperature and biosphere. This interplay between the environment and the biosphere has big implications for the development of the Earth’s atmosphere, and for the early Earth [1]. Most research for initial colonization of terrestrial rocks has focused on the role of lichens [10], while work on bacteria and their role in volcanic rock weathering was only recently elucidated with Actinobacteria, Proteobacteria and Bacteroidetes being found to be the dominant phyla [1, 2, 5, 11,12,13]
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