Isolation and characterisation of azoxystrobin degrading bacteria from soil

The first strobilurin fungicides were introduced in 1996, and have since been used in a vast array of disease/plant systems worldwide. The strobilurins now consist of 16 compounds and represent the 2nd most important fungicide group worldwide with 15% of the total fungicide market share. Strobilurins are moderately persistent in soil, and some degradation products (e.g. azoxystrobin acid) have been detected as contaminants of freshwater systems. Little is currently known about the transformation processes involved in the biodegradation of strobilurins or the microbial groups involved. Using sequential soil and liquid culture enrichments, we isolated two bacterial strains which were able to degrade the most widely used strobilurin, azoxystrobin, when supplied as a sole carbon source. 16S rRNA showed that the strains showed homology to Cupriavidus sp. and Rhodanobacter sp. Both isolated strains were also able to degrade the related strobilurin compounds trifloxystrobin, pyraclostrobin, and kresoxim-methyl. An additional nitrogen source was required for degradation to occur, but the addition of a further carbon source reduced compound degradation by approximately 50%. However, 14C radiometric analysis showed that full mineralisation of azosxystrobin to 14CO2 was negligible for both isolates. 16S rRNA T-RFLP analysis using both DNA and RNA extracts showed that degradation of azoxystrobin in soil was associated with shifts in bacterial community structure. However, the phylotypes which proliferated during degradation could not be attributed to the isolated degraders.