Lawrence Berkeley National Laboratory

The response of Desulfovibrio vulgaris Hildenborough (DvH), a sulphate-reducing bacterium, to nitrate stress was examined using quantitative proteomic analysis. DvH was stressed with 105 m M sodium nitrate(NaNO3), a level that caused a 50percent inhibition in growth. The protein profile of stressed cells was compared with that of cells grown in the absence of nitrate using the iTRAQ peptide labelling strategy and tandem liquid chromatography separation coupled with mass spectrometry (quadrupoletime-of-flight) detection. A total of 737 unique proteins were identified by two or more peptides, representing 22percent of the total DvH proteome and spanning every functional category. The results indicate that this was a mild stress, as proteins involved in central metabolism and the sulphate reduction pathway were unperturbed. Proteins involved in the nitrate reduction pathway increased. Increases seen in transport systems for proline, glycine^ betaineandglutamate indicate that the NaNO3 exposure led to both salt stress and nitrate stress.Up-regulation observed in oxidative stress response proteins (Rbr, RbO, etc.) and a large number of ABC transport systems as well as in iron ^ sulphur -cluster-containing proteins, however, appear to be specific to nitrate exposure. Finally, a number of hypothetical proteins were among the most significant changers, indicating that there may be unknown mechanisms initiated upon nitrate stress in DvH.