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

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.

Detergent-Stable Salt-Activated Proteinases from Virgibacillus halodenitrificans SK1-3-7 Isolated from Fish Sauce Fermentation.

The NaCl-activated and detergent-stable proteinases from Virgibacillus halodenitrificans SK1-3-7 isolated from fish sauce fermentation were purified and characterized. The enzymes with molecular masses of 20 and 36 kDa showed caseinolytic activity on a zymogram. Optimum azocaseinolytic activity was at 60 °C and pH 9. The proteolytic activity increased in the presence of 10 mM CaCl2 and 0.5 M NaCl and showed high stability at 0-2 M NaCl. The enzymes were stable at pH 4-10 and 10-50 °C. The enzymes preferably hydrolyzed Suc-Ala-Ala-Pro-Phe-pNA and were completely inhibited by phenylmethanesulfonyl fluoride (PMSF), showing subtilisin-like characteristics. Activity and stability remained high in the presence of H2O2 and various surfactants. The enzymes exhibited high stability (>95%) in various organic solvents (DMSO, butanol, ethanol, 2-propanol, and acetonitrile) at concentration of 50%. The V. halodenitrificans SK1-3-7 proteinases showed potential as a biocatalyst in aqueous-organic solvent systems and as an additive in laundry detergent.

Enhanced protease production in a polymethylmethacrylate conico-cylindrical flask by two biofilm-forming bacteria.

A polymethylmethacrylate (PMMA) conico-cylindrical flask (CCF) with an inner arrangement consisting of eight equidistantly spaced rectangular strips mounted radially on a circular disk to provide additional surface area for microbial attachment was employed for protease production by two biofilm-forming bacteria, an intertidal gamma-Proteobacterium (DGII) and a chicken meat isolate, Virgibacillus pantothenticus. The flask design allowed comparison of protease production during cultivation with a hydrophilic (glass) or hydrophobic (PMMA) surface. Compared to the Erlenmeyer flask, the CCF allowed protease production that was 30% and 35% higher and growth that was 20% and 345% higher for DGII and V. pantothenticus, respectively. Protease production increased by 202% and 22% and growth by 19,275% and 940% for DGII and V. pantothenticus, respectively, in the presence of a hydrophobic as compared to a hydrophilic surface. This investigation pioneers the application of a vessel beyond the traditional shake-flask for enhancing protease production by biofilm-formers.