Abstract
(1) Background: Microbial communities in terrestrial, calcifying high-alkaline springs are not well understood. In this study, we investigate the structure and composition of microbial mats in ultrabasic (pH 10–12) serpentinite springs of the Voltri Massif (Italy). (2) Methods: Along with analysis of chemical and mineralogical parameters, environmental DNA was extracted and subjected to analysis of microbial communities based upon next-generation sequencing. (3) Results: Mineral precipitation and microbialite formation occurred, along with mat formation. Analysis of the serpentinite spring microbial community, based on Illumina sequencing of 16S rRNA amplicons, point to the relevance of alkaliphilic cyanobacteria, colonizing carbonate buildups. Cyanobacterial groups accounted for up to 45% of all retrieved sequences; 3–4 taxa were dominant, belonging to the filamentous groups of Leptolyngbyaceae, Oscillatoriales, and Pseudanabaenaceae. The cyanobacterial community found at these sites is clearly distinct from creek water sediment, highlighting their specific adaptation to these environments.
Highlights
Carbonates, formed both abiogenically or biogenically, are among the most abundant minerals, and are essential in the long-term global carbon cycle [1]
Our study focuses on presence and abundance of these organisms colonizing pools just next to the outflows of the high-alkaline springs
All are oversaturated with respect to calcium carbonate
Summary
Carbonates, formed both abiogenically or biogenically, are among the most abundant minerals, and are essential in the long-term global carbon cycle [1]. As dissolved ions, they are the most important parameters for ocean alkalinity [2]. HCO3 − is converted to CO2 (for carbon dioxide fixation by the ribulose bisphosphate carboxylase enzyme) and a hydroxide ion, resulting in a shift to alkaline pH outside the cell. In aqueous solution, dissolved CO2 forms the weak acid H2 CO3 , resulting again in the formation of H+ and HCO3 − upon dissociation, which
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