Fabclavine biosynthesis in X. szentirmaii: shortened derivatives and characterization of the thioester reductase FclG and the condensation domain-like protein FclL.

Fabclavines, unusual peptide-polyketide-polyamine hybrids, show broad-spectrum bioactivity against a variety of different organism like Gram-positive and -negative bacteria, fungi and protozoa. We elucidated the biosynthesis of these NRPS-PKS hybrids in Xenorhabdus szentirmaii by deletion of most genes encoded in the fabclavine BGC and subsequent analysis of produced fabclavine or polyamine intermediates. Thereby, we identified shortened fabclavines similar to the bioactive zeamines. Furthermore, we analyzed the thioester reductase FclG and the free-standing condensation domain-like protein FclL in detail and observed low substrate specificity for both enzymes.