The Metalloid Reductase of Pseudomonas Moravenis Stanleyae Conveys Nanoparticle Mediated Metalloid Tolerance

In the present work we have identified a glutathione reductase like metalloid reductase (GRLMR) responsible for mediating selenite tolerance in Pseudomonas moravenis stanleyae through the enzymatic generation of Se(0) nanoparticles. This enzyme has an unprecedented substrate specificity for selenodiglutathione (K_m= 336 μM) over oxidized glutathione (K_m=8.22 mM). This enzyme was able to induce selenite tolerance in foreign bacterial cell lines by increasing the IC₉₀ for selenite from 1.9 mM in cell lacking the GRLMR gene to 21.3 mM for cells containing the GRLMR gene. It was later confirmed by STEM and EDS that Se nanoparticles were absent in control cells and present in cells expressing GRLMR. Structural analysis suggests the lack of a sulfur residue in the substrate/product binding pocket may be responsible for this unique substrate specificity.