Stenotrophomonas maltophilia SeITE02: a new bacterial strain suitable for bioremediation of selenite-contaminated environmental matrices

Biochemical and proteomic tools have been utilized for investigating the mechanism of action of a new Stenotrophomonas maltophilia strain (SeITE02), a gamma-proteobacterium capable of resisting to high concentrations of selenite (SeO3(2-), Se(IV)), reducing it to non-toxic elemental selenium under aerobic conditions, previously isolated from a selenite-contaminated mining soil. Biochemical analysis demonstrated that: a) nitrite reductase does not seem to take part in the process of selenite reduction by the bacterial strain SeITE02, although its involvement in this process had been hypothesized in other cases; b) nitrite strongly interferes with selenite removal when the two oxyanions (NO2(-) and SeO3(2-)) are simultaneously present, this suggesting that the two reduction/detoxification pathways share a common enzymatic step, probably at the level of cellular transport; c) selenite reduction, in vitro, does not take place in the membrane or periplasmic fractions, but only in the cytoplasm, where maximum activity is exhibited at pH 6.0 in presence of NADPH; d) glutathione is involved in the selenite reduction mechanism, since inhibition of its synthesis leads to a considerable delay in the onset of reduction. As far as the proteomic findings are concerned the evidence was reached that 0.2 mM selenite and 16 mM nitrite, when added to the culture medium, caused a significant modulation (ca. 10%, i.e. 96 and 85 protein zones, respectively) of the total proteins visualized in the respective 2D maps. These spots were identified by MS analysis and were found to belong to the following functional classes: nucleotide synthesis and metabolism; damaged-protein catabolism; protein and amino acid metabolism, carbohydrate metabolism, DNA-related proteins and proteins involved in cell division and oxidative stress.