Long-term intracellular chromium partitioning with subsurface bacteria

Copper bioaccumulation by the actinobacterium Amycolatopsis sp. AB0

Amycolatopsis sp. AB0, a copper resistant actinobacterium isolated from polluted sediments, has shown high copper specific biopsortion ability (25 mg g(-1)). Two approaches were used to confirm metal accumulation in growing cells of Amycolatopsis sp. AB0; we performed subcellular fractioning assays which showed that the retained copper was associated with the extra-cellular fraction (exopolymer, 40%), but mainly within the cells. Intracellular distribution of copper was: 86% in the cytosolic fraction, 11% at the cell wall and 3% associated with the ribosome/membrane fraction. Its copper bioaccumulation ability was corroborated by using silver enhanced staining of copper with the Timm's reagent technique, which has not been used to detect metal deposits in bacteria before. In addition, we constructed specific oligonucleotides for targeting genes coding for copper P-Type ATPases that could be involved in the copper uptake ability of this strain. A 607 bp DNA fragment was amplified and sequenced from Amycolatopsis sp AB0. BLAST search analysis showed 71% protein homology of the deduced sequence with a putative cation-transporting ATPase of Nocardia farcinica and 65% with a copper translocating ATPase of Mycobacterium flavescens. To our knowledge this is the first report of the presence of copper P-type ATPase genes in the Amycolotopsis genus.

Elemental analysis of uncultured magnetotactic bacteria exposed to heavy metals

Natural enrichments of magnetotactic bacteria were used to study the sites where heavy metals accumulate in uncultured bacteria. Most bacteria obtained by magnetic concentration from these enrichments contained, in addition to the magnetosomes, large phosphorus-rich granules in the cytoplasm. Metal (Zn, Mn, Sr, Cd, Al, Cr, and Pb) chlorides were added independently to the enrichments, and after 24 h, the elemental composition of the phosphorus-rich granules, magnetosomes, and "soft parts" (cytoplasm plus cell envelope) of whole bacteria was analyzed by energy-dispersive X-ray analysis on a transmission electron microscope. All bacteria contained Mn and Sr in the phosphorus-rich granules; some of them presented Mn peaks also in the soft parts. Zinc accumulation was variable and was found mainly in the phosphorus-rich granules, but also in the soft part of some bacteria. Some analyzed bacteria presented Zn peaks only in the soft parts, and some of them did not present Zn in any structure. Cadmium and Al were found only in the granules of some bacteria. Chromium was found in the soft parts of some bacteria. Lead was not detected in any bacteria. We concluded that the phosphorus-rich granules are major sites for metal accumulation by these bacteria. No conclusive results for magnetosomes were obtained because of the limitations of the analytical techniques particularly when used for whole cell analysis.Key words: magnetotactic bacteria, polyphosphate granules, heavy metals, uncultured bacteria, biomineralization, X-ray microanalysis.

Microbial mobilization and immobilization of heavy metals

Recent studies in the area of heavy metal biosorption and mobilization have addressed the selectivity of microbial sorbents in multimetal mixtures, the potential for metal uptake under natural environmental conditions, and the mechanisms of "reactions' between metals and microbes. Results from these studies have provided a better understanding of the potential for interactive effects in complex systems and may aid in the development of predictive models.