Key Role of Alphaproteobacteria and Cyanobacteria in the Formation of Stromatolites of Lake Dziani Dzaha (Mayotte, Western Indian Ocean)

Abstract

Lake Dziani Dzaha is a thalassohaline tropical crater lake located on the “Petite Terre” Island of Mayotte (Comoros archipelago, Western Indian Ocean). Stromatolites are actively growing in the shallow waters of the lake shores. These stromatolites are mainly composed of aragonite with lesser proportions of hydromagnesite, calcite, dolomite, and phyllosilicates. They are morphologically and texturally diverse ranging from tabular covered by a cauliflower-like crust to columnar ones with a smooth surface. High-throughput sequencing of bacterial and archaeal 16S rRNA genes combined with confocal laser scanning microscopy (CLSM) analysis revealed that the microbial composition of the mats associated with the stromatolites was clearly distinct from that of the Arthrospira-dominated lake water. Unicellular-colonial Cyanobacteria belonging to the Xenococcus genus of the Pleurocapsales order were detected in the cauliflower crust mats, whereas filamentous Cyanobacteria belonging to the Leptolyngbya genus were found in the smooth surface mats. Observations using CLSM, scanning electron microscopy (SEM) and Raman spectroscopy indicated that the cauliflower texture consists of laminations of aragonite, magnesium-silicate phase and hydromagnesite. The associated microbial mat, as confirmed by laser microdissection and whole-genome amplification (WGA), is composed of Pleurocapsales coated by abundant filamentous and coccoid Alphaproteobacteria. These phototrophic Alphaproteobacteria promote the precipitation of aragonite in which they become incrusted. In contrast, the Pleurocapsales are not calcifying but instead accumulate silicon and magnesium in their sheaths, which may be responsible for the formation of the Mg-silicate phase found in the cauliflower crust. We therefore propose that Pleurocapsales and Alphaproteobacteria are involved in the formation of two distinct mineral phases present in the cauliflower texture: Mg-silicate and aragonite, respectively. These results point out the role of phototrophic Alphaproteobacteria in the formation of stromatolites, which may open new perspective for the analysis of the fossil record.

Formation of magnesium‐smectite during lacustrine carbonates early diagenesis: Study case of the volcanic crater lake Dziani Dzaha (Mayotte – Indian Ocean)

“…Magnesium‐rich clay minerals, referred to as ‘Mg‐silicates’ in this study, are increasingly reported associated with ancient and modern carbonate rocks (e.g. Hover et al ., ; Bristow et al ., ; Wright, ; Zeyen et al ., , ; Pace et al ., ; Gérard et al ., ). In particular, Mg‐silicates have been reported in lacustrine carbonate reservoirs of the South‐Atlantic (e.g.…”

“…The variety of geological environments allowing Mg‐rich clays to form is unclear. In Phanerozoic rocks, the presence of Mg‐silicates has been attributed to different depositional environments, including weathering profiles developed on Mg‐rich rocks such as basic or ultrabasic igneous rocks (Huang et al ., ), hydrothermal settings where fluids interact with Mg‐rich igneous material (Setti et al ., ), alkaline lakes and evaporative basins (Van Denburgh, ; Yuretich & Cerling, ; Darragi & Tardy, ; Banfield et al ., ; Hay et al ., ; Hover et al ., ; Martini et al ., ; Bristow et al ., ; Zeyen et al ., , ; Pace et al ., ; Gérard et al ., ). Spring inflows into lakes hosted in basic volcanic terrains could also contribute to create the right set of conditions, i.e.…”

“…Present‐day sedimentary features can provide information about the palaeoenvironments where Mg‐rich clays formed. Sediments developed in lakes characterized by waters with high pH (>9), and either relatively high silica concentrations (Van Denburgh, ; Yuretich & Cerling, ; Darragi & Tardy, ; Banfield et al ., ; Hay et al ., ; Zeyen et al ., , ; Gérard et al ., ) or high magnesium concentrations (Hover et al ., ; Martini et al ., ), were found to host Mg‐silicates. To date, however, the specific geochemical conditions controlling their formation remain unclear.…”

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

“…In contrast, continental thalassohaline lakes that are permanently landlocked with hardly any exchange with the sea have been the focus of a limited number of investigations (Makhdoumi‐Kakhki, Amoozegar, Kazemi, Pašić, & Ventosa, ; Naghoni et al., ). Lake Dziani Dzaha (Mayotte) has been recently classified as a thalassohaline lake and presents several atypical features that make it an excellent model to examine the genetic structure and dynamics of microbial communities across environmental niches (Gérard et al., ; Leboulanger et al., ).…”

“…Lake Dziani Dzaha (Mayotte) has been recently classified as a thalassohaline lake and presents several atypical features that make it an excellent model to examine the genetic structure and dynamics of microbial communities across environmental niches (Gérard et al, 2018;Leboulanger et al, 2017).…”