The role of cyanobacteria in crystallization of magnesium calcites

Laboratory experiments showed the effect of the cyanobacterium Microcoleus chthonoplastes on the formation of magnesium calcites, using model solutions (2.14M MgCl₂-0.05M CaCl₂-0.6M NaCl-0.18M NaHCO₃). The conditions of existence of cyanobacteria in such solutions in light or darkness significantly alter the structure of the sediment and the shape and size of the carbonate crystals. Cyanobacteria slow down crystallization due to the formation of exometabolites with a chelating effect, which leads to the precipitation of high-magnesium calcites. In the photosynthetic environment the presence of huntite (CaMg₃(CO₃)₄), possible forerunner of dolomite, is prominent.     

Interaction of cyanobacteria with volcanic ashes

Capacity for growth in water suspensions of volcanic ashes was shown for two oscillatorian cyanobacterial isolates from different environments. Growth dynamics depended on the physicochemical characteristics of the ashes and on pH of the medium. During cyanobacterial growth, some elements were leached, which either stimulated or inhibited growth. These solubilized elements could be adsorbed on the mucous sheaths, mineralizing the trichomes. The extracellular polysaccharides excreted by cyanobacteria facilitated adhesion between the ash particles and the changes in their composition. These results suggest an analogy between the processes in the modern volcanogenic areas and the biological weathering on volcanic soils during the early period of life on Earth.     

Accumulation and precipitation of Mn2+ by the cells of Oscillatoria terebriformis

The cyanobacterium Oscillatoria terebriformis was shown to exhibit resistance to high manganese concentrations, remaining viable at 2.5 mM MnCl₂ in the medium. Cyanobacterial cells were capable of considerable manganese consumption from the medium. The dynamics of Mn sorption by the cells were the same in all experimental variants, independent of the manganese concentration. Manganese concentration in the biomass peaked after 2–3 days and depended on Mn²⁺ concentration in the medium and on the amount of biomass introduced. In the case of O. terebriformis, manganese removed from the medium may be subdivided into Mn absorbed by the cell, Mn bound to the cell wall, Mn absorbed by the glycocalix, and chemically precipitated Mn. Of the total 21.25 ± 1.0 mg of consumed manganese, biological absorption and chemical precipitation were responsible for 11.78 ± 0.98 and 9.2 ± 0.8 mg, respectively. In the presence of cyanobacteria, Mn removal from the medium was 2.28 times higher than in the control. This process depended considerably on Mn sorption by exopolysaccharides. At 1.3 mM Mn²⁺, a lamellar mat was formed with interlayers of manganese carbonate.     

Transformation of carbonate minerals in a cyano-bacterial mat in the course of laboratory modeling

A laboratory model of a cyano-bacterial mat with mineral layers of carbonates was used to examine the dynamics of the transformation of calcium-magnesium carbonate under the conditions of a soda lake. The activity of various organisms of the cyanobacterial community results in conditions under which the Ca-Mg carbonate precipitate undergoes changes. The crystal lattice of the initial carbonate is restructured; its mineralogical composition changes depending on the conditions of the mat. In magnesium calcites, which are formed under such low-temperature conditions, a rudimentary cation adjustment can occur with the formation of dolomite domains. These experiments confirm the hypothesis that the dolomite found in stromatolites is of a secondary origin and can be formed in the course of transformation of Ca-Mg carbonates under alkaline conditions in an alkaliphilic cyanobacterial community.     

Laboratory Simulations of Cyanobacterial Mats of the Alkaline Geochemical Barrier

The goal of this work was to illustrate a possible interaction between the soda continent and the ocean. A laboratory simulation was undertaken of the development of alkaliphilic mat with calcium carbonate and calcium phosphate interlayers in the zone where ocean waters, containing calcium and manganese, come into contact with carbonate- and phosphate-rich alkaline waters. The macrostructure of the layered cyanobacterial mat turned out to be little dependent on the chemical conditions causing sediment formation. The chemical composition of freshly formed mineral interlayers of the mat was found to vary with the medium composition. The mineralogical composition of the sediment is determined by diagenesis conditions in its depth, which can cause mineral phase conversions.     

Experimental associations of cyanobacteria and actinomycetes

Associations of cyanobacteria with actinomycetes are not being investigated. The purpose of this study is to investigate the biological aspects of coexistence of the free-living Anabaena variabilis with actinomycetes isolated from apogeotropic roots of Strangeria eriopus and Cycas micholitzii; with the cyanobacterium Oscillatoria terebriformis (Ag.) Elenk. emend., which were isolated from the natural cyanobacterial mat taken from the Kamchatkan thermal spring; and with actinomycetes isolated from the accumulating culture of cyanobacterium. Positive tropism of actinomycete hyphae to cyanobacterial trichomes and that of the cyanobacterium to streptomycetes were observed. Stimulation of growth of O. terebriformis in the associated culture with the streptomycete was recorded. The increase of fixation of nitrogen by A. variabilis and of photosynthetic activity of O. terebriformis in the associated culture with the streptomycete was recorded.     

Significance of bacteria in natural and experimental sedimentation of carbonates, phosphates, and silicates

The role of bacteria in sedimentation of phosphorites, siliceous and carbonate rocks is discussed. Preservation of bacterial bodies in fossil condition, even in very ancient deposits, is connected with their very early mineralization. A series of laboratory experiments allowed conditions to be reproduced that could have led to mineralization of cyanobacteria and their preservation in sedimentary deposits. The experiments have also shown the important role of cyanobacteria and their metabolic products in the formation of some carbonate minerals, as well as in the accumulation of stromatolites.