Formation of stromatolite lamina at the interface of oxygenic–anoxygenic photosynthesis

Abstract

In modern stromatolites, mineralization results from a complex interplay between microbial metabolisms, the organic matrix, and environmental parameters. Here, we combined biogeochemical, mineralogical, and microscopic analyses with measurements of metabolic activity to characterize the mineralization processes and products in an emergent (<18 months) hypersaline microbial mat. While the nucleation of Mg silicates is ubiquitous in the mat, the initial formation of a Ca-Mg carbonate lamina depends on (i) the creation of a high-pH interface combined with a major change in properties of the exopolymeric substances at the interface of the oxygenic and anoxygenic photoautotrophic layers and (ii) the synergy between two major players of sulfur cycle, purple sulfur bacteria, and sulfate-reducing bacteria. The repetition of this process over time combined with upward growth of the mat is a possible pathway leading to the formation of a stromatolite.

Carbonate Precipitation in Mixed Cyanobacterial Biofilms Forming Freshwater Microbial Tufa

“…The microscopic observations combined with the FT-IR spectroscopy demonstrate that cyanobacterial EPS control crystal morphology of carbonates and spatial distribution of the precipitates. A similar arrangement of carbonate precipitates (i.e., on cyanobacterial sheets and/or within the EPS matrix of the biofilm, in close proximity of cyanobacteria) has been reported in hypersaline [24,26], marine [28][29][30] and freshwater [17,54] biofilms or microbial mats containing cyanobacteria. A comparison of experimental and natural samples suggested that the lamellae precipitating on the surface of Phormidiaceae filaments and the micro-peloids associated with Oscillatoriaceae were the main carbonate crystal morphologies.…”

“…The first one is through studying naturally-occurring modern or ancient organomineral (e.g. [1,[22][23][24][25][26][27][28][29][30]). The main difficulty of this approach is the interpretation of multiple, steep chemical and physical gradients and complex, interconnected microbial processes that vary over both space and time.…”

Biotic–Abiotic Influences on Modern Ca–Si-Rich Hydrothermal Spring Mounds of the Pastos Grandes Volcanic Caldera (Bolivia)

“…Three main biological communities were differentiated based on morphological observations of mats in the field: green microbial mats, black microbial mats, and diatoms. A common feature throughout La Salsa is the abundance of diatoms and bacteria usually embedded in Extracellular Organic Matter (EOM), the main site for mineral precipitation [64][65][66]. Both diatoms and bacteria are associated in all mat types, either as main producers, or trapped in the EOM.…”

“…Thin sections ( Figure 8D) and micro-XRF mapping ( Figure 15A) reveal that CaCO 3 content corresponds to micritic clusters and blocky calcite cements. Clusters are probably the result of local microbial activity in mats [65,120], while cements are related to very early diagenesis in dewatered parts of the mats. Locally, the abundance of diatoms and cyanobacteria can increase pH, due to their high level of photosynthetic activity, thus favoring carbonate precipitation in the mat [28,121].…”

Conserved bacterial genomes from two geographically distinct peritidal stromatolite formations shed light on potential functional guilds

“…Oxygenic photosynthesis by Cyanobacteria results in rapid fixation of carbon dioxide and an increase alkalinity [30]. Carbonate ions bind cations such as calcium and are precipitated under alkaline conditions, promoting the growth of stromatolite structures [1].…”