Heavy Metal Tolerance in Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an aerobic, non-fermentative Gram-negative bacterium widespread in the environment. S. maltophilia Sm777 exhibits innate resistance to multiple antimicrobial agents. Furthermore, this bacterium tolerates high levels (0.1 to 50 mM) of various toxic metals, such as Cd, Pb, Co, Zn, Hg, Ag, selenite, tellurite and uranyl. S. maltophilia Sm777 was able to grow in the presence of 50 mM selenite and 25 mM tellurite and to reduce them to elemental selenium (Se0) and tellurium (Te0) respectively. Transmission electron microscopy and energy dispersive X-ray analysis showed cytoplasmic nanometer-sized electron-dense Se0 granules and Te0 crystals. Moreover, this bacterium can withstand up to 2 mM CdCl2 and accumulate this metal up to 4% of its biomass. The analysis of soluble thiols in response to ten different metals showed eightfold increase of the intracellular pool of cysteine only in response to cadmium. Measurements by Cd K-edge EXAFS spectroscopy indicated the formation of Cd-S clusters in strain Sm777. Cysteine is likely to be involved in Cd tolerance and in CdS-clusters formation. Our data suggest that besides high tolerance to antibiotics by efflux mechanisms, S. maltophilia Sm777 has developed at least two different mechanisms to overcome metal toxicity, reduction of oxyanions to non-toxic elemental ions and detoxification of Cd into CdS

Reactivity studies of the tyrosyl radical in ribonucleotide reductase from Mycobacterium tuberculosis and Arabidopsis thaliana--comparison with Escherichia coli and mouse.

International audienceRibonucleotide reductase (RNR) is a key enzyme for DNA synthesis since it provides cells with deoxyribonucleotides, the DNA precursors. Class I alpha2beta2 RNRs contain a dinuclear iron center and an essential tyrosyl radical in the beta2 component (protein R2). This is also true for the purified protein R2 of Mycobacterium tuberculosis RNR, as shown by iron analysis, light absorption and EPR spectroscopy. EPR spectroscopy at 286 GHz revealed a high g(x) value, suggesting that the radical is not hydrogen bonded, as in other prokaryotic R2s and in contrast with eukaryotic R2s (from Arabidopsis thaliana and mouse). Furthermore, it proved to be very resistant to scavenging by a variety of phenols and thiols and by hydroxyurea, similar to the Escherichia coli radical. By comparison, the plant and mouse radicals are very sensitive to drugs such as resveratrol and 2-thiophenthiol. The radical from M. tuberculosis RNR does not seem to be an appropriate target for new antituberculous agents

Structural Environment and Stability of the Complexes Formed Between Calmodulin and Actinyl Ions

International audienceThe interaction site of neptunyl with the calmodulin and electronic density. The complexation of uranium(VI) and neptunium(V) was investigated with recombinant one-site variant of the calmodulin N-terminal domain, denoted CaM-WT. The combination of experimental results (UV−vis and extended X-ray absorption fine structure spectroscopy) and density functional theory (DFT) calculations revealed that the coordination sphere of uranyl is pH dependent, while netunyl’s stays the same at every pH studied. The DFT calculations showed that at physiological pH the complex formed between the protein and the netunyl is more stable than the one formed with uranyl