Structure and function of microbial communities involved in biomineralization

Different aspects of carbonate precipitation are considered in this study. The first part examines carbonates in a model system that helps to explain the initial steps in the formation of so-called concretions, which are solidified sedimentary masses, cemented with carbonate minerals. Formation of carbonate concretions under participation of microorganisms is common in oceans and in freshwater systems and is also considered as an important fossilization process. The role of the involved microbial communities, however, is largely unknown. In this study, siderite (FeCO3) formation in microbial microcosms, mimicking processes in marine sediments, is observed. For inoculation, Wadden Sea sediments were used and fatty acyl compounds (lipids, surfactants) served as substrates. In actively growing microcosms, sulfate reducing bacteria (the genus Desulfofrigus in particular) dominate the microbial community. Submicroscopic mineral precipitates forming on bacterial cell surfaces were identified as siderite (FeCO3). This biologically influenced mineralization process may, in the natural environment, initiate the formation of large concretions under suboxic conditions in coastal sediments. In the second part of this study, a natural carbonate precipitating system was considered. Calcification in terrestrial, highly alkaline springs, is an obvious process; the participation of microorganisms, however, is not well understood. Serpentinization-driven springs of the Voltri Massif (Italy) expel highly alkaline fluids (pH 10-12); precipitated calcite forms soft layers and solidified sinter terraces. Metagenomics studies, based on analysis of 16 amplicons, were used for identification of the microbial communities growing as biofilms intermixed with calcite structures. Few cyanobacterial genera dominated these communities. The general discussion considers the formation of organominerals and preservation of biological macromolecules in different carbonate precipitating systems.2022-02-0

Cyanobacterial Mats in Calcite-Precipitating Serpentinite-Hosted Alkaline Springs of the Voltri Massif, Italy

(1) Background: Microbial communities in terrestrial, calcifying high-alkaline springs are not well understood. In this study, we investigate the structure and composition of microbial mats in ultrabasic (pH 10–12) serpentinite springs of the Voltri Massif (Italy). (2) Methods: Along with analysis of chemical and mineralogical parameters, environmental DNA was extracted and subjected to analysis of microbial communities based upon next-generation sequencing. (3) Results: Mineral precipitation and microbialite formation occurred, along with mat formation. Analysis of the serpentinite spring microbial community, based on Illumina sequencing of 16S rRNA amplicons, point to the relevance of alkaliphilic cyanobacteria, colonizing carbonate buildups. Cyanobacterial groups accounted for up to 45% of all retrieved sequences; 3–4 taxa were dominant, belonging to the filamentous groups of Leptolyngbyaceae, Oscillatoriales, and Pseudanabaenaceae. The cyanobacterial community found at these sites is clearly distinct from creek water sediment, highlighting their specific adaptation to these environments

Purification and characterization of thiol dependent, oxidation-stable serine alkaline protease from thermophilic Bacillus sp.

Alkaline serine protease was purified to homogeneity from culture supernatant of a thermophilic, alkaliphilic Bacillus sp. by 80% ammonium sulphate precipitation followed by CM-cellulose and DEAE-cellulose ion exchange column chromatography. The enzyme was purified up to 16.5-fold with 6900 U/mg activity. The protease exhibited maximum activity towards casein at pH 8.0 and at 80 °C. The enzyme was stable at pH 8.0 and 80 °C temperature up to 2 h. The Ca2+ and Mn2+ enhanced the proteolytic activity up to 44% and 36% as compared to control, respectively. However, Zn2+, K+, Ba2+, Co2+, Hg2+ and Cu2+ significantly reduced the enzyme activity. PMSF (phenyl methyl sulphonyl fluoride) completely inhibited the protease activity, whereas the activity of protease was stimulated up to two folds in the presence of 5 mM 2-mercaptoethanol. The enzyme was also stable in surfactant (Tween-80) and other commercial detergents (SDS, Triton X-100)