[14-16] Bongkrekic acid is a highly unsaturated tricarboxylic fatty acid, which inhibits oxidative phosphorylation by blocking the mitochondrial adenine nucleotide translocator.[15] Recently, the biosynthesis of the deadly toxin catalysed by an unusual polyketide synthase (PKS) was elucidated allowing for a better understanding of the pathogenicity of the contaminating bacteria.[17, 18] Besides bongkrekic acid, B. gladioli pv. cocovenenans is also known to produce the azapteridine toxoflavin (2), which might as well contribute to the toxic properties of contaminated tempe bongkrek.[19] Several recent studies indicated that Burkholderia

species are prolific producers of secondary metabolites with potent biological and pharmacological GSK-3 assay properties.[20-28] Interestingly, some species were also found to be associated with mucoralean fungi and are of eminent metabolic importance for the fungi.[4,

29] A prominent example are the bacterial endosymbionts of R. microsporus.[30] The bacteria, Burkholderia rhizoxinica,[31] are producers of highly active antitumoural agents as well as a strong hepatotoxin.[32, 33] The discovery of these natural products is of importance as R. microsporus is not only a plant pathogen but also implicated with human infections.[6] In this regard it should be noted that full genome sequencing of natural product producing this website bacteria indicated that their biosynthetic potential may even be much higher than expected.[34] It is believed that the majority of secondary metabolite encoding GNA12 genes is only expressed under certain conditions and may require a specific trigger.[35] To get an overview of the secondary metabolic capabilities

of the toxinogenic B. gladioli strain and to investigate its metabolic contribution to the bacterial–fungal interaction, we performed a systematic survey on its biosynthetic potential on a genomic and an analytical-chemical level. Here, we report the formation and the biosynthesis of a class of antibiotics previously not known to be produced by these fungus-associated bacteria. We also describe the context-dependent production of the antibiotics and of the toxin bongkrekic acid in the fungal–bacterial coculture. Rhizopus microsporus var. oligosporus HKI 0401 (CBS 337.62; ATCC 46348; NRRL514) and Burkholderia gladioli pv. cocovenenans HKI 10521 (DSM 11318; ATCC 33664) were grown on potato dextrose agar (PDA) at 30 °C. Genomic DNA of B. gladioli was isolated using the MasterPure™ DNA purification kit (Epicentre Biotechnologies, Hessisch Oldendorf, Germany) to perform 454 Shotgun sequencing combined with a 3 kb paired end library. An approximately 25-fold coverage including 10 scaffolds was obtained and subsequent correct assembly of the generated contigs were achieved using the Lasergene SeqMan software (DNA Star, Inc., Madison, WI, USA).