Horizontal gene transfer confers fermentative metabolism in the respiratory-deficient plant trypanosomatid Phytomonas serpens

► Characterisation of the gene for a pyruvate/indolepyruvate decarboxylase (PDC/IPDC) of P. serpens. ► Conservation of PDC/IPDC gene sequence in 14 Phytomonas isolates. ► Phylogenetic analysis suggests a horizontal gene transfer event from a donor phytobacteria. ► PDC activity measured in P. serpens lysates. ► The acquisition of a PDC activity in Phytomonas represents an important metabolic adaptation.