Carbonate and silicate biomineralization in a hypersaline microbial mat (Mesaieed sabkha, Qatar): Roles of bacteria, extracellular polymeric substances and viruses

Abstract

In a modern peritidal microbial mat from Qatar, both biomediated carbonates and Mg‐rich clay minerals (palygorskite) were identified. The mat, ca 5 cm thick, shows a clear lamination reflecting different microbial communities. The initial precipitates within the top millimetres of the mat are composed of Ca–Mg–Si–Al–S amorphous nanoparticles (few tens of nanometres) that replace the ultrastructure of extracellular polymeric substances. The extracellular polymeric substances are enriched in the same cations and act as a substrate for mineral nucleation. Successively, crystallites of palygorskite fibres associated with carbonate nanocrystals develop, commonly surrounding bacterial bodies. Micron‐sized crystals of low‐Mg calcite are the most common precipitates, together with subordinate aragonite, very high‐Mg calcite/dolomite and ankerite. Pyrite nanocrystals and framboids are present in the deeper layers of the mat. Calcite crystallites form conical structures, circular to triangular/hexagonal in cross‐section, evolving to crystals with rhombohedral terminations; some crystallite bundles develop into dumb‐bell and stellate forms. Spheroidal organo‐mineral structures are also common within the mat. Nanospheres, a few tens of nanometres in diameter, occur attached to coccoid bacteria and within their cells; these are interpreted as permineralized viruses and could be significant as nuclei for crystallite‐crystal precipitation. Microspheres, 1 to 10 μm in diameter, result from intracellular permineralization within bacteria or the mineralization of the bacteria themselves. Carbonates and clay minerals are commonly aggregated to form peloids, tens of microns in size, surrounded by residual organic matter. Magnesium silicate and carbonate precipitation are likely to have been driven by pH – saturation index – redox changes within the mat, related to microenvironmental chemical changes induced by the microbes – extracellular polymeric substances – viruses and their degradation.

Characterization of modern dolomite stromatolites from hypersaline Petukhovskoe Soda Lake, Russia

“…; Perri et al . ). The limitation in Ca 2+ supply can be a reason of the specific sequence of Mg–Si–Ca precipitation in Petukhovskoe soda lake stromatolites.…”

Precipitation of Calcium Carbonate Mineral Induced by Viral Lysis of Cyanobacteria

“…When Ca 2+ access to intracellular space, the existence of capsid synthetized by viral DNA provides nucleation site for initial calcification (Fig 10). This heterogeneous calcification involves addition of material to the preexisting viral surface, which may similar to mineralized virus in microbial mat from hot spring (Peng et al, 2013) or hypersaline lakes (Pacton et al, 2014;De Wit et al, 2015;Perri et al, 2017). The pathway that viral induced calcification during the lysis of the 15 host cells retrieved by experimental study expands roles of viruses in marine carbonate precipitation.…”

“…10). 5 Preliminary investigations have also demonstrated that viruses from the hypersaline lake occur and are incorporated in biogenic carbonate, suggesting that virus may be mistaken for nanobacteria and play a role in initiating mineralization (De Wit et al, 2015;Pacton et al, 2014;Perri et al, 2017). The viral drive during the biogenic carbonate precipitation in hypersaline lakes is attributed to either an indirect route, involving silicified viruses as an intermediate phase during diagenesis (Pacton et al, 2014) or a direct incorporation of amino acids polymerized with viral proteins into growing high-Mg calcite crystals (De 10 Wit et al, 2015).…”

“…The influence of photosynthesis on CaCO3 precipitation in general is based either on the uptake mechanism of inorganic carbon (Riding, 2006;Riding, 2011) or surface-induced mechanisms involving the cell surface or extracellular polymers as preferential sites for mineral nucleation (Obst et al, 2009b). With regard to viruses numbering, usually ten times more than their hosts (Suttle, 2005(Suttle, , 2007, viruses have been recognized as new agents of the nucleation site for the carbonate mineral (De Wit et al, 2015;Perri et al, 2017) and can influence carbonate chemistry notably 30 (Lisle and Robbins, 2016). However, the viral influence on the "whiting event" is hardly know.…”

“…The study of the hot spring biofilm by Peng et al (2013) proved that viruses can be preserved in the natural environment. Recent studies have shown that hypersaline carbonate minerals can precipitate at the surface of viral particles and have implication to the nano-sized calcium carbonate structures in various geological settings (Pacton et al, 2014;Lisle and Robbins, 2016;Perri et al, 2017). All of the above viral mineralization studies are focused on heterogeneous nucleation, which occurs at nucleation sites on surfaces and is assumed to be much more common than 15 homogeneous nucleation (Sear, 2014).…”