, 2006; Zhao et al., 2006). As such, we initially aimed to clone the multimodular PKS gene cluster dedicated to galbonolide biosynthesis by targeting the methoxymalonyl-ACP biosynthesis locus. Unexpectedly, there was no typical multimodular PKS gene within the cloned 42-kb region (Fig. 2 and Supporting Information, Table S1). Instead, the galGHIJK locus is neighbored by three genes that encode KAS-related proteins, which are orf3, orf4, and orf5. The product of orf3 is homologous to the KAS III (FabH-type) protein, but it is missing the catalytic cysteine

residue. Orf4 protein has a complete KAS domain that is followed by an amino-terminally truncated KAS domain. Orf4 also contains the β-ketoacyl-ACP reductase domain(s), but does not have an ACP domain. Orf5 contains buy PF-562271 an AT domain and a thiolation motif, which are conserved in ACP domains. An interesting feature is that orf4 and orf5 have homologues in various Burkholderia strains, including Burkholderia multivorans (Fig. S1), but their biological role is unclear. A galI-disruption mutant was generated with the gene-disruption

plasmid selleck chemicals pD-galI. The genotype of the resulting mutant SK-galI-5 was confirmed by Southern analysis using the 800-bp galI fragment as a probe (Fig. 3a and b). A 3.2-kb KpnI fragment was present in the wild-type (WT) chromosome and it was absent in the SK-galI-5 chromosome. In the lane of the SK-galI-5 sample, three bands with approximate sizes of 4.6, 5.9, and 7.4 kb were found. The 4.6- and 5.9-kb fragments likely originated from the integration of pD-galI into the galI region (Fig. 3b), while the 7.4-kb band corresponds to pD-galI itself. It was thus concluded that galI was successfully disrupted in SK-galI-5. It was initially hypothesized that SK-galI-5 would be incapable Racecadotril of synthesizing galbonolide A, but would retain the ability to produce galbonolide B. In this case, the extracts of SK-galI-5 would display a negligible level of antifungal activity, as compared with those of WT, because galbonolide

B is several hundred times less potent than galbonolide A when tested against C. neoformans (Harris et al., 1998). As expected, the supernatant extract of SK-galI-5 displayed a negligible level of antifungal activity, as compared with the WT extract (Fig. 3c). However, comparable levels of activity were observed in the mycelia extracts of both WT and SK-galI-5 (Fig. 3d). It is unknown whether S. galbus has the potential to accumulate antifungal substance(s), other than galbonolide A, when cultured under the conditions used here. To answer this question, a silica gel-TLC separation was coupled with the antifungal activity assay. With the TLC conditions used, the retardation factor (Rf) value for galbonolide B was reported to be 0.35 (Abe et al., 1985), but there are no comparable data available for galbonolide A.