Bacteria and fungi associated with isoprene consumption in soil

Isoprene is a reactive volatile organic compound released from the biosphere that can be abundant in the planetary boundary layer, where it can have a myriad of effects on atmospheric chemistry and secondary aerosol formation. There is currently a high degree of uncertainty in forecasts of how atmospheric isoprene concentrations will shift in response to anthropogenic land-use change and climate change. One source of this uncertainty is that studies of terrestrial isoprene fluxes have almost entirely focused on plant sources of isoprene, largely ignoring the role of soils as a sink of isoprene and the corresponding microbial consumption of isoprene. We quantified isoprene consumption rates by the microbial communities found in two distinct soils under laboratory conditions and used high-throughput sequencing to identify the bacterial and fungal taxa that increased in relative abundance with changes in isoprene mixing ratios. On average, soil microbes were capable of consuming 68% (ranging 55% to 80%) of the gaseous isoprene provided to the soils (2–200 ppbv) in a flow-through experiment. Consumption rates increased with increasing levels of isoprene with rates reaching 770 pmol g –1 h –1 in one of the soils exposed to the highest mixing ratio of isoprene (200 ppbv). Increases in isoprene levels were associated with significant shifts in the composition of both soil bacterial and fungal communities. A wide range of taxa were associated with isoprene consumption including members of the Actinobacteria, Proteobacteria, Gemmatimonadetes, and Zygomycota phyla with many of the taxa being closely related to known hydrocarbon degraders. Soils likely represent a significant sink of atmospheric isoprene and our results suggest that a wide range of bacterial and fungal taxa are capable of isoprene degradation.