Functional analysis of desaturases from the myxobacterium Myxococcus xanthus

The fatty acid (FA) profiles of myxobacteria contain FA species with double bonds at the Delta(5) and Delta(11) positions, the latter being rather unusual among bacteria. Despite this knowledge, the mechanism for introduction of these double bonds has never been described before in myxobacteria. Searches for candidate genes in the genome of the model organism Myxococcus xanthus revealed 16 genes, which have been annotated as FA desaturases. However, due to redundant substrate specificity, functional analyses of these enzymes by construction of inactivation mutants did not lead to the identification of their function or substrate specificity. Therefore, we elucidated the regioselectivity of the desaturation reactions by heterologous expression of eight desaturases from M. xanthus in Pseudomonas putida and thus could prove five of them to be indeed active as desaturases, with three (MXAN_1742, MXAN_3495 and MXAN_5461) and two (MXAN_0317 and MXAN_6306) acting as Delta(5) and Delta(11) desaturases, respectively. This is the first report about the heterologous expression and regioselectivity of FA desaturases in myxobacteria.