CaCO3 Precipitation in Multilayered Cyanobacterial Mats: Clues to Explain the Alternation of Micrite and Sparite Layers in Calcareous Stromatolites

Abstract

Marine cyanobacterial mats were cultured on coastal sediments (Nivå Bay, Øresund, Denmark) for over three years in a closed system. Carbonate particles formed in two different modes in the mat: (i) through precipitation of submicrometer-sized grains of Mg calcite within the mucilage near the base of living cyanobacterial layers, and (ii) through precipitation of a variety of mixed Mg calcite/aragonite morphs in layers of degraded cyanobacteria dominated by purple sulfur bacteria. The δ13C values were about 2‰ heavier in carbonates from the living cyanobacterial zones as compared to those generated in the purple bacterial zones. Saturation indices calculated with respect to calcite, aragonite, and dolomite inside the mats showed extremely high values across the mat profile. Such high values were caused by high pH and high carbonate alkalinity generated within the mats in conjunction with increased concentrations of calcium and magnesium that were presumably stored in sheaths and extracellular polymer substances (EPS) of the living cyanobacteria and liberated during their post-mortem degradation. The generated CaCO3 morphs were highly similar to morphs reported from heterotrophic bacterial cultures, and from bacterially decomposed cyanobacterial biomass emplaced in Ca-rich media. They are also similar to CaCO3 morphs precipitated from purely inorganic solutions. No metabolically (enzymatically) controlled formation of particular CaCO3 morphs by heterotrophic bacteria was observed in the studied mats. The apparent alternation of in vivo and post-mortem generated calcareous layers in the studied cyanobacterial mats may explain the alternation of fine-grained (micritic) and coarse-grained (sparitic) laminae observed in modern and fossil calcareous cyanobacterial microbialites as the result of a probably similar multilayered mat organization.

Carbonate Precipitation in Mixed Cyanobacterial Biofilms Forming Freshwater Microbial Tufa

“…In the biological incubations, a sequence of biofilm development and mineral precipitation was observed in all treatments. The cyanobacteria showed a growth pattern presumably coinciding with EPS production and excretion of photorespiration products, similar to reports for biofilms (during a similar time frame as in our experiment; [64]) and microbial mats [6,10,29,30]. The different types of cyanobacterial metabolisms and their specific effect on the physicochemical conditions are summarized in Table 3.…”

“…Similar changes in physicochemical measurements (e.g., increases in pH, SIcalcite) were reported in laboratory experiments [32][33][34][35][36]54] and during manipulations in the field [29,30]. It should be noted that the physicochemical conditions in the biofilm, which is composed predominantly of cyanobacteria and EPS, could have been different than those of the overlying water.…”

“…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.…”

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

“…Anoxygenic photosynthesis by PSB contributes to carbonate precipitation (Ionescu et al, 2015;Kremer, Kazmierczak, & Stal, 2008;Visscher & Stolz, 2005;Visscher et al, 1998). In laboratory manipulations of mats from Niva Bay, the green cyanobacterial layer produced mostly <1 μm HMC crystals and the red PSB layer formed >1 μm HMC crystals and aragonite, presumably due to differences in EPS composition between the two layers (Kaźmierczak et al, 2015).…”

Macroscopic, optical and diffraction assessment of encrustations and SEM analyses of phototrophic microbial mats from wellheads and select zones of emergence of mineral water in Serbia

“…The product of this process, elemental sulphur, can be deposited in the form of fine granules on the filament surface, which is no longer oxidized except in the presence sulfur oxidizing bacteria. Therefore, if calcium is present in high concentrations, they can facilitate the formation of various morphotypes of gypsum minerals (EDINGER, 1973;TANG et al, 2014;KAŹMIERCZAK et al, 2015).…”