Copper economy of denitrification by soil microbes

Bioavailable (fixed) nitrogen is a key limiting factor for crop production. However, a significant portion
is lost via denitrification, an essential metabolic process in major soil microbes, in which bioavailable
nitrate is reduced to inert dinitrogen gas. These reactions proceed via a conserved and copperexpensive
pathway that involves two multicopper enzymes, including a nitrite reductase (NirK). Hence
rates of denitrification correlate with copper availability. Critically, copper is a prevalent heavy metal
contaminant in topsoil, a legacy from the prolonged use of copper-derived agricultural biocides. It has
been shown that denitrification rates (hence loss of fixed nitrogen) are greater in contaminated vs. noncontaminated
soils.

We are interested in how bacteria acquire and insert nutrient copper into multicopper enzymes,
particularly NirK. Previous work in the group has shown that activation of NirK in vivo requires a
periplasmic factor called PCuC. In the absence of PCuC, NirK is produced in the metal-free form. We
hypothesise that PCuC is a metallochaperone that catalyses copper insertion into NirK. Our results may
identify strategies for improving crop production in copper-rich regions.