Rapid Nitrate Reduction Assay with Intact Microbial Cells or Spores

Abstract

Many microorganisms have the capacity to use nitrate as a respiratory electron acceptor. Reduction of nitrate is catalyzed by a multi-subunit nitrate reductase that is often located associated with the cytoplasmic membrane and has its active site oriented toward the cytoplasm. This means that nitrate must be transported into the cell and often this occurs concomitantly with the export of the reduced nitrite product. Often nitrate and nitrite transport are coupled through the action of a nitrate: nitrite antiporter. Microbial cells, spores and mycelium harbour intracellular storage compounds such as trehalose or glycogen that, upon metabolism, function as endogenous electron donors for nitrate reduction. It is also possible to use glucose supplied exogenously as a substrate for nitrate reduction. The method described here allows the direct analysis of nitrate reduction by whole cell material without the requirement for artificial electron donors. This method is also applicable to the study of spores, particularly those of Streptomyces species (Fischer et al., 2013). The paper by Fischer et al. 2013 provides examples of datasets for the method presented below.