Biogeochemical cycling of isoprene
There is a natural biogeochemical cycle for isoprene (2-methyl-1,3-butadiene). Terrestrial plants emit to the atmosphere around 600 Tg (600 million tonnes) of isoprene per year which is approximately the same amount as methane. Other sources of isoprene include terrestrial and marine microbes and isoprene is also synthesised for the industrial production of poly-isoprene (artificial rubber).
Isoprene is a volatile and hydrocarbon, with important effects on atmospheric chemistry. Isoprene in the troposphere leads to the formation of ozone. Ozone can act directly as a greenhouse gas and also controls the lifetime of other greenhouse gases, hence, isoprene has a potent effect on global warming. Conversely, isoprene may encourage climate cooling by contributing to the formation of aerosols, which increases cloud formation and causes reduced radiative forcing
As much as 50% of the methane produced in terrestrial environments is consumed by microbes before it escapes to the atmosphere. However, we know very little about biological consumption of isoprene in the environment or its biogeochemical cycle. As with methane, much of the isoprene produced in the biosphere may be consumed by microbes before it is released to the atmosphere. Will isoprene emissions to the atmosphere increase due to growth of high isoprene emitting trees such as poplar and willow which are increasingly grown for biofuels, and will isoprene consumption in the biosphere increase to counteract this?
It is vital that we understand the role microbes play in the isoprene cycle in the environment.
We are studying the bacterium Rhodococcus AD45, which contains a soluble diiron centre monooxygenase of the same enzyme family as soluble methane monooxygenase. This isoprene monooxygenase enzyme is involved in the initial oxidation step of isoprene metabolism. We are looking at the physiology, biochemistry and molecular biology of Rhodococcus AD45 and other newly isolated bacteria from terrestrial and marine environments that grow on isoprene. We also want to develop cultivation-independent methods to study the distribution, diversity and activity of isoprene degraders in the environment in order to assess their roles in the biogeochemical cycling of isoprene.
This research has been funded by a grant from the Natural Environment Research Council (2011-2015).