A LABORATORY-SCALE ALKALINE-LAKE MODEL OF MICROBE-ZEOLITE INTERACTIONS

Modern trona-producing alkaline-saline lakes provide an aqueous environment rich in monovalent cations capable of producing authigenic sedimentary zeolite minerals, such as erionite, by alteration of trachyte glass. These environments also support prolific populations of haloalkaliphilic archaea and bacteria. Periodic precipitation – desiccation cycles result in dilution and evaporative concentration of pore waters with pore fluid chemistry fluctuating in ion concentration and pH. Ultimately, evaporation to dryness results in alkaline carbonate mineral precipitation.

Within these biologically harsh fluctuating environments, microbial archaea maintain osmotic balance by adjusting their intracellular ion concentration through accumulation and discharge of K⁺. Erionite consists of a three-dimensional framework of (Si,Al)O₄ tetrahedra linked to form channel structures. Substitution of Al³⁺ for Si⁴⁺ results in a net negative charge balanced by extra-framework cations such as Na⁺ or K⁺ held within the channel structures; erionite has a strong preference for K⁺. H₂O molecules also occupy the channel structures. Extra-framework cations and H₂O are mobile and may be added or removed during precipitation – desiccation cycles. It is hypothesized that as evaporation and desiccation progress, microorganisms may associate with erionite to exploit the mobile K⁺ ions and water, in a sense using the erionite as a lifeboat for survival.

To explore this hypothesis, Natrialba magadii, a microbial archaea isolate from Lake Magadi in East Africa, was cultured in the laboratory in the presence and absence of erionite. Samples where evaporated to dryness under aerobic conditions and resulting mineral phases and desiccated microbes were documented using scanning electron microscopy with energy dispersive x-ray analysis. Preliminary results reveal unique mineral morphologies developed in inoculated erionite-containing samples compared to sterile controls and non-erionite samples suggesting the erionite-microbial relationship influences mineral morphology.