Nitrous oxide (N2O) is estimated to contribute up to 9% of the global radiative forcing of greenhouse gas emissions. Agriculture accounts for ~70% of anthropogenic atmospheric loading of N2O, which is largely microbial in origin. Understanding the environmental factors that control N2O production and consumption by microbes is a critical and major challenge on the road to developing practical mitigation strategies for N2O emissions. Denitrifying bacteria play an important global role in the synthesis and consumption of N2O, but very little work has been done on studying the regulatory networks that modulate the assembly and activity of the biochemical apparatus that catalyses production and destruction of the greenhouse gas.

Critically, N2O reduction is dependent on the Cu-containing enzyme NosZ. As arable lands become more intensively exploited Cu-deficiency is also becoming a more acute global concern. For example, it was recently estimated that around ~20% of arable lands in Europe are biologically Cu deficient. We have shown that under nitrate-rich, Cu-depleted conditions, denitrifying bacterial cultures release N2O at >100 times the rate of Cu-replete cultures. We have undertaken the first global transcription analysis of a denitrifying respiratory network and this has shown a clear regulation of the nos genes by Cu, which leads to the down-regulation of the NosZ enzyme. From an environmental point of view this is potentially significant because it leads to the emission of N2O. The resulting impact on N2O release is very pronounced with 40% of nitrate input into the system being released as this potent greenhouse gas.

The problem of N2O emission by bacteria is recognised globally as a huge environmental issue. In recognition of this a prestigious University Scholarship is available for a PhD programme to study the biochemistry of the assembly and regulation of the enzyme that destroy nitrous oxide, NosZ. The research programme will include protein expression, protein biochemistry, protein structure and spectroscopy and protein-DNA interaction studies.

Richardson, D., Felgate, H., Watmough, N., Thomson, A., and Baggs, E. (2009) Mitigating release of the potent greenhouse gas N2O from the nitrogen cycle - could enzymic regulation hold the key? Trends in Biotechnology 27: 388-397.