Microdiverse types of Thiobacillus ferrooxidans and their interactions with uranium

Sequence analysis of the 16S rRNA genes of several reference strains and uranium mining waste pile isolates of Thiobacillus ferrooxidans revealed specific signatures which distinguish three types within the species. This allowed to develop a technique for analysis of the distribution of the T. ferrooxidans eco-types in the soil samples of a uranium mining waste pile.
The technique is based on amplification of 16S rDNA fragments in total soil DNA by the use of two T. ferrooxidans species specific primers 16S458F and 16S1473R (De Wulf-Durand et al., 1997). The resulting amplicons were then digested with a frequently cutting enzyme RsaI which produced three different type-specific profiles (Selenska-Pobell et al., 2000). Using this direct approach we have demonstrated that one of the T. ferrooxidans types (type I) was predominant in the soil samples studied and was found in more polluted sites, whereas the type II was found in less contaminated samples. The type III was found mostly to coexist with the type II.
The complexation of uranium by the three eco-types of T. ferrooxidans was investigated. The uranium sorption studies showed that the strains from the three different types possess different capability to accumulate uranium. The process of uranium accumulation is affected by the initial uranium concentration and pH. Using sodium carbonate as a desorbing agent, 97% of the biosorbed uranium was recovered from the cells of T. ferrooxidans type III, and 88.33 and 88.50% from the cells of the type I and II, respectivley. Extended x-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopy were performed to obtain information about the exact chemical structure of the uranium complexes formed on the surfaces of the three eco-types of T. ferrooxidans.