Thiobacillus caldus and Leptospirillum ferrooxidans are widely distributed in continuous flow biooxidation tanks used to treat a variety of metal containing ores and concentrates

Abstract

Using 16S rDNA-based techniques, several workers have reported that Leptospirillum ferrooxidans and Thiobacillus thiooxidans are the bacteria most commonly encountered in biooxidation processes for the treatment of copper by heap leaching as well as the treatment of zinc-lead or arsenopyrite concentrates by continuous-flow tank leaching. We have compared the 16S rRNA genes from four strains of Thiobacillus caldus and identified two restriction enzymes which permit the 16S rDNA from T. caldus to be distinguished from closely related strains of T. thiooxidans . DNA has been isolated directly from continuous-flow biooxidation tanks treating copper, nickel or arsenopyrite concentrates at 40–55 °.By examining the restriction enzyme patterns of the amplified 16S rDNA, we report that even at 40 °C it is the moderate thermophile T. caldus , rather than T. thiooxidans , which is the dominant sulphur-oxidising bacterium in these tanks. By examining the restriction enzyme patterns of the 16S rDNA from fifteen strains of Leptospirillum spp isolated from different parts of the world, we have confirmed that the leptospirilli can be divided into two major groups. Furthermore, we have found that the leptospirilli which dominate the iron-oxidising bacteria in the continuous-flow biooxidation tanks belong to the same sub-group as the L. ferrooxidans type strain (DSM2705).Restriction enzyme maps of the 16S rDNA which enable isolates of T. ferrooxidans, T. thiooxidans, T. caldus and the subgroups of the genus Leptospirillum to be readily distinguished from each other are presented.