Abstract

Many bacteria are known to produce a wide range of biomedically important secondary metabolites synthesized by type I polyketide synthases (PKSs). These enzymes own a modular structure that could be used for combinatorial biosynthesis to yield novel drug candidates. To directly access PKS gene diversity of soil and seawater in China, a set of degenerate oligonucleotide primers were designed to amplify the ketoacyl synthase (KS)fragments belonging to the PKS I genes from the soil and the seawater samples. Twenty-three (23) new KS fragments were obtained. Their predicted amino acid sequences showed 45 to 85% identifies to the known KS domains in the GenBank. Phylogenetic analysis indicated that 14 of them belonged to the “normal” KS groups that catalyzed the condensation of the acyl groups and the other nine KS fragments belonged to the hybrid PKS/NRPS (non-ribosomal peptide synthase) groups which used an amino acid moiety as a starter unit. All the four KS fragments isolated from the seawater belonged to the former group. No significant difference was found between the soil KS fragments and the seawater KS fragments. Several KS fragments were endowed with some distinct characters that will be useful as probes for future studies.

Key words: Uncultured microorganisms, polyketide synthase, ketoacyl synthase, soil, seawater.