Transcriptional Response of Selenopolypeptide Genes and Selenocysteine Biosynthesis Machinery Genes inEscherichia coliduring Selenite Reduction

Abstract

Bacteria can reduce toxic selenite into less toxic, elemental selenium (Se0), but the mechanism on how bacterial cells reduce selenite at molecular level is still not clear. We usedEscherichia colistrain K12, a common bacterial strain, as a model to study its growth response to sodium selenite (Na2SeO3) treatment and then used quantitative real-time PCR (qRT-PCR) to quantify transcript levels of threeE. coliselenopolypeptide genes and a set of machinery genes for selenocysteine (SeCys) biosynthesis and incorporation into polypeptides, whose involvements in the selenite reduction are largely unknown. We determined that 5 mM Na2SeO3treatment inhibited growth by∼50% while 0.001 to 0.01 mM treatments stimulated cell growth by∼30%. Under 50% inhibitory or 30% stimulatory Na2SeO3concentration, selenopolypeptide genes (fdnG,fdoG, andfdhF) whose products require SeCys but not SeCys biosynthesis machinery genes were found to be induced ≥2-fold. In addition, one sulfur (S) metabolic geneiscSand two previously reported selenite-responsive genessodAandgutSwere also induced ≥2-fold under 50% inhibitory concentration. Our findings provide insight about the detoxification of selenite inE. colivia induction of these genes involved in the selenite reduction process.