Abstract
Interactions of a facultative anaerobic bacterial isolate named Paenibacillus sp. JG-TB8 with U(VI) were studied under oxic and anoxic conditions in order to assess the influence of the oxygen-dependent cell metabolism on microbial uranium mobilization and immobilization. We demonstrated that aerobically and anaerobically grown cells of Paenibacillus sp. JG-TB8 accumulate uranium from aqueous solutions under acidic conditions (pH 2 to 6), under oxic and anoxic conditions. A combination of spectroscopic and microscopic methods revealed that the speciation of U(VI) associated with the cells of the strain depend on the pH as well as on the aeration conditions. At pH 2 and pH 3, uranium was exclusively bound by organic phosphate groups provided by cellular components, independently on the aeration conditions. At higher pH values, a part (pH 4.5) or the total amount (pH 6) of the dissolved uranium was precipitated under oxic conditions in a meta-autunite-like uranyl phosphate mineral phase without supplying an additional organic phosphate substrate. In contrast to that, under anoxic conditions no mineral formation was observed at pH 4.5 and pH 6, which was clearly assigned to decreased orthophosphate release by the cells. This in turn was caused by a suppression of the indigenous phosphatase activity of the strain. The results demonstrate that changes in the metabolism of facultative anaerobic microorganisms caused by the presence or absence of oxygen can decisively influence U(VI) biomineralization.
Highlights
The rapid industrial growth during the last century has introduced different types of pollutants in the environment
The main objective of the present study was to investigate the interactions of the facultative anaerobic isolate JG-TB8 with U(VI) under oxic and anoxic conditions, in order to determine the influence of the different cell metabolism on the uranium immobilization by this strain
The 16S rRNA gene of the studied in this work bacterial isolate JG-TB8 shared 99.5% sequence identity with that of the bacterial strain Paenibacillus sp. 436-1, recovered from a soil sample from Wisconsin (USA) (Fig. S1 in File S1)
Summary
The rapid industrial growth during the last century has introduced different types of pollutants in the environment. One of the big challenges of the third millennium is the management of radioactive waste and the protection of humans and the environment from its chemical and radiological toxicity [1]. The remediation procedures of uranium-polluted sites and waste piles in most cases only include a covering of the surface to prevent from direct radiation as well as from the release of radon gas or radioactive dusts. In particular the uranyl ion (UO22+), which predominates under acidic (,pH 5) and nonreducing conditions [3], has a high mobility and biological toxicity, which is based on both, its chemical and radiological properties. The speciation and the mobility of uranium in nature is affected by a variety of abiotic [4,5] and biotic [6,7]
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