Heavy Metal Bioremediation by Anaerobic-Thermophilic Bacteria from the Great Artesian Basin

Abstract

Bioremediation is considered an effective environmental remedial strategy when compared with physical and chemical techniques. Microorganisms can remove and detoxify pollutants by transforming or degrading them. A large portion of these toxic pollutants are heavy metals that are present naturally or due to anthropogenic activities. Bacteria inhabiting areas that have high levels of heavy metals have adapted to resist and reduce these pollutants. In the current, study heavy metal transforming bacteria have been isolated, characterised and investigated for bioremediation and biodegradation capabilities. The Great Artesian Basin (GAB) in Australia is a unique thermal site that harbours diverse microbial communities. Anaerobic and facultative anaerobic, thermophilic and thermotolerant bacteria were isolated from groundwaters and run-off waters from the GAB region. A total of 6 bacteria were isolated and identified as belonging to Anoxybacillus, Thermobrachium, Caloramator, and Virgibacillus genera using the 16S rRNA. Heavy metal reduction capacity was tested on all of the isolates. Strain VY was best at reducing vanadium(V), up to 10mM. Strain COY reduced up to 8 mM of cobalt(III). Strain SEY showed the most significant reduction of selenium(III). Strain FEY had the highest extent of iron(III) reduction. Strains CRG and CRL could reduce chromium(VI) most efficiently. Additional tests were done to fortify the selection of an optimal candidate for heavy metal bioremediation. These tests included biosurfactant production, for which all strains exhibited at least a 32% reduction in surface tension after 24 hours. The second test was biofilm formation where strains SEY and CRG performed best forming a medium rated biofilm under aerobic conditions but a poor biofilm under anaerobic conditions. A third test was to measure the chemotactic ability of the strains and strain SEY demonstrated the ability to possess a chemical attraction towards iron(III). From the characterisation tests and regarding bioremediation potential, strain SEY, an Anoxybacillus sp., was the most promising. This isolate had improved vanadium(V) and iron(III) reduction rates of over 50% in co-cultivation symbiosis tests with strains CRL and FEY, respectively.