Mapping of polyketide biosynthesis pathways in Aspergillus nidulans using a genome wide PKS gene deletion library

In order to map new links between PKS genes and their products in Aspergillus nidulans we have systematically deleted all thirty-two individual genes predicted to encode polyketide synthases in this model organism. This number greatly exceeds the number of currently known PKs calling for new approaches for triggering “cryptic” or “silent” genes to see production of compounds not previously observed under laboratory conditions.

We therefore decided to challenge our deletion library on eight different complex media, spanning a large variety of alternating carbon and nitrogen sources, vitamins and other nutrients. Comparative UHPLC-DAD analyses indeed revealed that a large number of secondary metabolites were produced by the A. nidulans reference strain on the different media.

Careful investigation, also including LC-DAD-HRMS data, has lead to the linking of several known compounds to their PKS genes. For example we have found that a whole series of prenylated PKs such as arugosins and shamixanthones can be linked to the mdpG PK gene cluster. Previously only emodins and monodictyphenone were known gene products of mdpG.

Further examples of new links between PK products and genes will be given illustrating the scope of using of diode array detection and electrospray in the negative mode for detection and tentative identification of non reduced polyketides.