BIO-CLAYS · Bio-clays from several water media

Bio-clays from several water media

Previous state-of-the-art The interaction of microorganisms with silicate minerals has been a matter of study for a number of years and knowledge has been accumulated on the interaction of individual microbial species with individual minerals. Our Bio-Clays project We identified the need for a more systematic approach in which comparison of results within a single project could provide perspective to our knowledge about the formation of clay mediated by microorganisms in different water media. Our project consisted of: Experiments of natural waters (spring, seawater, freshwater lake, hypersaline water) with volcanic glass. The experiments were divided in two parts: 1) biological experiments, in which the growth of the original microbial content of the natural waters was encouraged by adding organic nutrients and exposure to light; 2) inorganic experiments, in which the biological growth was suppressed by lack of nutrients and by carrying out the experiments in the dark. Project development and follow-up The experiments lasted 18 months. Shorter-term experiments were tested to investigate the microbial development and water chemistry. The microbial development in the biological experiments was spectacular. The chemical analysis of the waters supplied an important background against which to interpret the results obtained from the chemical transformation of the volcanic glass. The analysis of the microbial species in the experiments became less successful as the study progressed, probably due to the difficulty to avoid DNA contamination in the large microbial colonies that developed. About 40 species of bacteria, fungi and algae were isolated by culture and identified at some level of their taxonomic tree. The large development of microbial colonies was an important element of the study because it maximized the effect of the biological experiments. Results The longest experiments (18 months) were investigated to identify the clays formed and the effect that the several water chemistry and biological control had on such clay formation. We also investigated the interface between the microbial mat and the glass grains. Figure 1 shows an instance of clay formation in direct contact with the microbial mat. At this early stage of the interpretation of our data, the main results from the overall study appear to be the following: 1) The composition of the glass is more important than water chemistry in controlling the type of clay formed. This is a very important conclusion to understand how mineral transformation reactions take place. 2) The main microbial action affecting clay formation is to encapsulate the glass in the microbial mat and generate chemical conditions which are very different from the bulk of the water. This is another important conclusion clarifying microbial action on minerals. 3) There is no evidence for the microbial action to accelerate clay formation, unless perhaps in the hypersaline water, due to the very chemically aggressive brine generated inside the microbial mat. Impact This project has been successful in establishing a comparison of the influence of water chemistry and microbial effect on clay formation. This shows clearly the main controls at the early stages of clay formation. This information is of great relevance for scientists working on geo-microbiology and on surface reaction studies. The knowledge obtained in this project can be applied to: 1) Obtain more accurate models of mineral transformation and mineral-microbe interaction at large scale. 2) Improve efficiency of microbial-mineral engineered processes, as used in environmental or industrial applications. Contact: Javier Cuadros, Natural History Museum, London SW7 5BD, UK, j.cuadros@nhm.ac.uk Beytullah Afsin, Department of Chemistry, Faculty of Science and Arts, Ondokuz Mayis University, Kurupelit, Samsun 55139 Turkey

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