Influence of temperature, salinity and Mg2+:Ca2+ ratio on microbially-mediated formation of Mg-rich carbonates by Virgibacillus strains isolated from a sabkha environment

Abstract

Studies have demonstrated that microbes facilitate the incorporation of Mg2+ into carbonate minerals, leading to the formation of potential dolomite precursors. Most microbes that are capable of mediating Mg-rich carbonates have been isolated from evaporitic environments in which temperature and salinity are higher than those of average marine environments. However, how such physicochemical factors affect and concur with microbial activity influencing mineral precipitation remains poorly constrained. Here, we report the results of laboratory precipitation experiments using two mineral-forming Virgibacillus strains and one non-mineral-forming strain of Bacillus licheniformis, all isolated from the Dohat Faishakh sabkha in Qatar. They were grown under different combinations of temperature (20°, 30°, 40 °C), salinity (3.5, 7.5, 10 NaCl %w/v), and Mg2+:Ca2+ ratios (1:1, 6:1 and 12:1). Our results show that the incorporation of Mg2+ into the carbonate minerals is significantly affected by all of the three tested factors. With a Mg2+:Ca2+ ratio of 1, no Mg-rich carbonates formed during the experiments. With a Mg2+:Ca2+ ratios of 6 and 12, multivariate analysis indicates that temperature has the highest impact followed by salinity and Mg2+:Ca2+ ratio. The outcome of this study suggests that warm and saline environments are particularly favourable for microbially mediated formation of Mg-rich carbonates and provides new insight for interpreting ancient dolomite formations.

High Mg/Ca Molar Ratios Promote Protodolomite Precipitation Induced by the Extreme Halophilic Bacterium Vibrio harveyi QPL2

“…The precipitation of bacterially-induced dolomite is usually associated with and restricted by particular conditions, especially the solution temperature, the sulfate concentration, salinity, and increasing Mg/Ca molar ratio ( Sánchez-Román et al, 2011 ; Qiu et al, 2017 ; Al Disi et al, 2019 ; Liu et al, 2019 ). For example, protodolomite has been induced by Haloferax volcanii DS52 in a medium with salinity (NaCl) higher than 200‰ ( Qiu et al, 2017 ), whereas aragonite and monohydrocalcite were formed in other conditions.…”

“…The interactions between bacteria and the above-mentioned ambient factors have been examined in previous studies. (1) A higher solution temperature is certainly favorable for dolomite precipitation (e.g., Al Disi et al, 2019 ), leading to increases in MgCO 3 and cation ordering in both abiotic and the biotic experiments ( Malone et al, 1996 ; Al Disi et al, 2019 ), since elevated temperature increases the saturation index of carbonate minerals ( Arvidson and Mackenzie, 1999 ). A higher temperature is also beneficial for overcoming kinetic obstacles to precipitation ( Rodriguez-Blanco et al, 2015 ).…”

“…(2) The presence of sulfate does not inhibit low-temperature bacterially-induced dolomite precipitation in natural environments (e.g., Vasconcelos and McKenzie, 1997 ) or under laboratory conditions ( Sánchez-Román et al, 2009 ), contrary to earlier indications ( Baker and Kastner, 1981 ). (3) High salinity facilitates dolomite precipitation mediated by halophilic bacteria ( Qiu et al, 2017 ; Al Disi et al, 2019 ). Experiments have shown that an increase in salinity enhances the amount of carboxylated molecules on the cell surface (mainly the acidic amino acids), leading to the nucleation of protodolomite ( Qiu et al, 2017 ).…”

Controlling pore-scale processes to tame subsurface biomineralization

“…Lower temperatures have been shown to alter bacterial growth and metabolism in a manner that increased the availability of precursors for EPS biosynthesis, thereby increasing EPS production (Gorret et al 2001 ). Saline environments are favorable for microbial formation of Mg-rich carbonates (Al Disi et al 2019 ). Indeed, environmental shifts from low- to high- salinity has been shown to increase the fraction of carboxylic groups on EPS, suggesting that such shifts could increase the Mg-consuming precipitation of dolomite (Diloreto et al 2021 ).…”

Mapping mineralogical heterogeneities at the nm-scale by scanning electron microscopy in modern Sardinian stromatolites: Deciphering the origin of their laminations

“…pH, temperature, Mg/Ca, salinity) on the precipitation of microbially mediatedMg-carbonates (Al Disi et al, 2019. For instance, in a sabkha environment, salinity, temperature, Mg/Ca (AlDisi et al, 2019) and carbonate supply(Al Disi et al, 2021) have a strong effect on bacterial activity, which in turn affect the incorporation of Mg within the calcite.…”