Health, Safety & Environment

Selenate and nitrate

Discovery of piperonal-converting oxidase involved in the metabolism of a botanical aromatic aldehyde

Piperonal-catabolizing microorganisms were isolated from soil, the one (strain CT39-3) exhibiting the highest activity being identified as Burkholderia sp. The piperonal-converting enzyme involved in the initial step of piperonal metabolism was purified from strain CT39-3. Gene cloning of the enzyme and a homology search revealed that the enzyme belongs to the xanthine oxidase family, which comprises molybdoenzymes containing a molybdopterin cytosine dinucleotide cofactor. We found that the piperonal-converting enzyme acts on piperonal in the presence of O2, leading to formation of piperonylic acid and H2O2. The growth of strain CT39-3 was inhibited by higher concentrations of piperonal in the culture medium. Together with this finding, the broad substrate specificity of this enzyme for various aldehydes suggests that it would play an important role in the defense mechanism against antimicrobial compounds derived from plant species.

Doi, S., Hashimoto, Y., Tomita, C., Kumano, T., and Kobayashi, M.,Discovery of piperonal-converting oxidase involved in the metabolism of a botanical aromatic aldehyde, Scientific Reports, 2016, 6.

Biosynthesis of selenate reductase in Salmonella enterica: critical roles for the signal peptide and DmsD

Salmonella enterica serovar Typhimurium is a Gram-negative bacterium with a flexible respiratory capability. Under anaerobic conditions, S. enterica can utilize a range of terminal electron acceptors, including selenate, to sustain respiratory electron transport. The S. enterica selenate reductase is a membrane-bound enzyme encoded by the ynfEFGH-dmsD operon. The active enzyme is predicted to comprise at least three subunits where YnfE is a molybdenum-containing catalytic subunit. The YnfE protein is synthesized with an N-terminal twin-arginine signal peptide and biosynthesis of the enzyme is coordinated by a signal peptide binding chaperone called DmsD. In this work, the interaction between S. enterica DmsD and the YnfE signal peptide has been studied by chemical crosslinking. These experiments were complemented by genetic approaches, which identified the DmsD binding epitope within the YnfE signal peptide. YnfE signal peptide residues L24 and A28 were shown to be important for assembly of an active selenate reductase. Conversely, a random genetic screen identified the DmsD V16 residue as being important for signal peptide recognition and selenate reductase assembly.

Connelly, K. R. S., Stevenson, C., Kneuper, H., and Sargent, F.,Biosynthesis of selenate reductase in Salmonella enterica: critical roles for the signal peptide and DmsD, Microbiology-Sgm, 2016, 162, 2136-2146.

Some of the common themes and variations between the different classes of nitrate and selenate reductases are reviewed.

Watts, C.A., Ridley, H., Dridge, E. J., Leaver, J. T., Reilly, A. J., Richardson, D. J., and Butler, C. S., Microbial reduction of selenate and nitrate: common themes and variations, Biochemical Society Transactions, 2005, 33, 173-175.