Spatiotemporal variations in microbial diversity across the three domains of life in a tropical thalassohaline lake (Dziani Dzaha, Mayotte Island)

Abstract

Thalassohaline ecosystems are hypersaline environments originating from seawater in which sodium chloride is the most abundant salt and the pH is alkaline. Studies focusing on microbial diversity in thalassohaline lakes are still scarce compared with those on athalassohaline lakes such as soda lakes that have no marine origin. In this work, we investigated multiple facets of bacterial, archaeal and eukaryotic diversity in the thalassohaline Lake Dziani Dzaha using a metabarcoding approach. We showed that bacterial and archaeal diversity were mainly affected by contrasting physicochemical conditions retrieved at different depths. While photosynthetic microorganisms were dominant in surface layers, chemotrophic phyla (Firmicutes or Bacteroidetes) and archaeal methanogens dominated deeper layers. In contrast, eukaryotic diversity was constant regardless of depth and was affected by seasonality. A detailed focus on eukaryotic communities showed that this constant diversity profile was the consequence of the high predominance of Picocystis salinarum, while nondominant eukaryotic groups displayed seasonal diversity turnover. Altogether, our results provided an extensive description of the diversity of the three domains of life in an unexplored extreme environment and showed clear differences in the responses of prokaryotic and eukaryotic communities to environmental conditions.

Morphology and Ecology of Two New Amoebae, Isolated From a Thalassohaline Lake, Dziani Dzaha

“…In previous studies, it has been reported that the season and/or the depth in the lake can influence its microbial diversity (Bernard et al, 2019;Hugoni et al, 2018). To see whether the two FLA isolates were influenced by these parameters, we performed a specific qPCR on DNA isolated from the water lake sampled in April (end of the rainy season) and November (dry season) 2015.…”

“…Lake water is warm (29-35°C) over the whole year and depth; pH is alkaline, classically between 9 and 9.5 depending on the season. The lake Dziani Dzaha microbial planktonic community has recently been described via a metabarcoding approach (Hugoni et al, 2018). Bacterial and archaeal diversity was influenced mainly by the sampling depth, whereas dry and rainy seasons alternations drove changes in vertical segregation of microorganisms.…”

Carbon isotope evidence for large methane emissions to the Proterozoic atmosphere

“…Dziani Dzaha is a shallow tropical volcanic crater lake on the Petite Terre Island of Mayotte (Comoros Archipelago, Indian Ocean) 28 , which is located 50 km west of a huge submarine volcano triggered in 2018 29 . Several surveys have been conducted to determine the lake biological, physical and chemical characteristics [30][31][32][33][34] (see details in Supplementary Information and Supplementary Fig. S1).…”

“…The water temperature is of ≈ 30 °C with little depth and seasonal variations. The ecosystem biomass is extremely high 30 and it is limited to microbial organisms 34 , with stromatolitic constructions thriving in the shallow parts of the lake (Supplementary Information).…”

“…This is only higher than the maximum value estimated in the Black Sea, which is another euxinic system overlain with at least 60 m of oxic water, where organic matter burial was estimated to 0.5-1.8% 61,66 (0.1% in the present-day oceans). In Dziani Dzaha, the very high productivity, the very thin oxic surface layer, the low sulphate concentrations, the shallow water column and the high sedimentation rate (close to 1.2 mm year −1 ) [30][31][32][33][34] , all create highly favourable conditions for the preservation and burial of organic matter [67][68][69] . By analogy, the value of 2.9% could be thus considered as a maximum for the organic burial rate in Precambrian oceans that were also microbially dominated, anoxic and sulphate-poor.…”