Hyper-resistance to arsenic in bacteria isolated from an antimony mine in South Africa

Soil and water sites were sampled at a South African antimony mine with elevated levels of arsenic due to the refining process. Enriched media yielded two pure bacterial cultures able to grow in both arsenite and arsenate. These were identified as Stenotrophomonas maltophilia SA Ant 15 and Serratia marcescens SA Ant 16. Stenotrophomonas maltophilia SA Ant 15 was resistant to 10 mmol l super(-1) arsenite and 20 mmol l super(-1) arsenate, whereas S. marcescens SA Ant 16 grew in 15 mmol l super(-1) arsenite and in up to 500 mmol l super(-1)arsenate, making it the most arsenic-resistant organism described to date. During growth, addition of arsenate or arsenite anions adversely affected biomass production and maximum specific growth rate and, in some instances, longer lag phases were induced. Reduction of arsenate to arsenite partly accounted for the high tolerance of the bacteria to arsenate. Our results suggest the use of these hyper-resistant bacteria as remediation agents in areas where arsenic contamination is prohibitively high.