Abstract
(1) Background: The geothermal spring of La Crouen (New Caledonia) discharges warm (42 °C) alkaline water (pH~9) enriched in dissolved nitrogen with traces of methane, but its microbial diversity has not yet been studied. (2) Methods: Cultivation-dependent and -independent methods (e.g., Illumina sequencing and quantitative PCR based on 16S rRNA gene) were used to describe the prokaryotic diversity of this spring. (3) Results: Prokaryotes were mainly represented by Proteobacteria (57% on average), followed by Cyanobacteria, Chlorofexi, and Candidatus Gracilibacteria (GN02/BD1-5) (each > 5%). Both potential aerobes and anaerobes, as well as mesophilic and thermophilic microorganisms, were identified. Some of them had previously been detected in continental hyperalkaline springs found in serpentinizing environments (The Cedars, Samail, Voltri, and Zambales ophiolites). Gammaproteobacteria, Ca. Gracilibacteria and Thermotogae were significantly more abundant in spring water than in sediments. Potential chemolithotrophs mainly included beta- and gammaproteobacterial genera of sulfate-reducers (Ca. Desulfobacillus), methylotrophs (Methyloversatilis), sulfur-oxidizers (Thiofaba, Thiovirga), or hydrogen-oxidizers (Hydrogenophaga). Methanogens (Methanobacteriales and Methanosarcinales) were the dominant Archaea, as found in serpentinization-driven and deep subsurface ecosystems. A novel alkaliphilic hydrogenotrophic methanogen (strain CAN) belonging to the genus Methanobacterium was isolated, suggesting that hydrogenotrophic methanogenesis occurs at La Crouen.
Highlights
Several thermal springs associated with low-temperature serpentinization can be found in the southeastern part of the main island of New Caledonia, either on land or in the southern lagoon [1,2,3,4]
At the northern end of the “Massif du Sud”, which is the main part of the New Caledonia ophiolite, several springs can be found near the city of Canala in a very fractured area at the transition between autochthonous sediments and the southern peridotite nappe [4]
The spring we have studied is located at La Crouen
Summary
Several thermal springs associated with low-temperature serpentinization can be found in the southeastern part of the main island of New Caledonia, either on land or in the southern lagoon [1,2,3,4]. At the northern end of the “Massif du Sud”, which is the main part of the New Caledonia ophiolite, several springs can be found near the city of Canala in a very fractured area at the transition between autochthonous sediments and the southern peridotite nappe [4]. Data reported for two of these springs showed that they discharge alkaline water (pH~9) at ~42 ◦ C [3,5]. The geological environment and the chemical composition of the La Crouen waters differ from those of the hyperalkaline springs located down south in the Prony Bay. There, Microorganisms 2021, 9, 1360.
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