title: PCR screening reveals considerable unexploited biosynthetic potential of ansamycins and a mysterious family of AHBA-containing natural products in actinomycetes.
abstract: OBJECTIVE
  Ansamycins are a family of macrolactams that are synthesized by type I polyketide synthase (PKS) using 3-amino-5-hydroxybenzoic acid (AHBA) as the starter unit. Most members of the family have strong antimicrobial, antifungal, anticancer and/or antiviral activities. We aimed to discover new ansamycins and/or other AHBA-containing natural products from actinobacteria.
  
  
  RESULTS
  Through PCR screening of AHBA synthase gene, we identified 26 AHBA synthase gene-positive strains from 206 plant-associated actinomycetes (five positives) and 688 marine-derived actinomycetes (21 positives), representing a positive ratio of 2·4-3·1%. Twenty-five ansamycins, including eight new compounds, were isolated from six AHBA synthase gene-positive strains through TLC-guided fractionations followed by repeated column chromatography. To gain information about those potential ansamycin gene clusters whose products were unknown, seven strains with phylogenetically divergent AHBA synthase genes were subjected to fosmid library construction. Of the seven gene clusters we obtained, three show characteristics for typical ansamycin gene clusters, and other four, from Micromonospora spp., appear to lack the amide synthase gene, which is unusual for ansamycin biosynthesis. The gene composition of these four gene clusters suggests that they are involved in the biosynthesis of a new family of hybrid PK-NRP compounds containing AHBA substructure.
  
  
  CONCLUSIONS
  PCR screening of AHBA synthase is an efficient approach to discover novel ansamycins and other AHBA-containing natural products.
  
  
  CONCLUSIONS
  This work demonstrates that the AHBA-based screening method is a useful approach for discovering novel ansamycins and other AHBA-containing natural products from new microbial resources.
authors.affiliation: State Key Laboratory of Microbial Technology, School of Life Sciences, Shandong University, Jinan, China.
authors.forename: H-X
authors.initials: HX
authors.lastname: Wang
authors.forename: Y-Y
authors.initials: YY
authors.lastname: Chen
authors.forename: L
authors.initials: L
authors.lastname: Ge
authors.forename: T-T
authors.initials: TT
authors.lastname: Fang
authors.forename: J
authors.initials: J
authors.lastname: Meng
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
authors.forename: X-Y
authors.initials: XY
authors.lastname: Fang
authors.forename: S
authors.initials: S
authors.lastname: Ni
authors.forename: C
authors.initials: C
authors.lastname: Lin
authors.forename: Y-Y
authors.initials: YY
authors.lastname: Wu
authors.forename: M-L
authors.initials: ML
authors.lastname: Wang
authors.forename: N-N
authors.initials: NN
authors.lastname: Shi
authors.forename: H-G
authors.initials: HG
authors.lastname: He
authors.forename: K
authors.initials: K
authors.lastname: Hong
authors.forename: Y-M
authors.initials: YM
authors.lastname: Shen
mesh_terms: D039903:Actinobacteria / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D062365:Aminobenzoates / Q000378:metabolism; D001688:Biological Products / Q000378:metabolism*; D006836:Hydro-Lyases / Q000145:classification / Q000235:genetics*; D062385:Hydroxybenzoates / Q000378:metabolism; D047029:Lactams, Macrocyclic / Q000378:metabolism*; D008848:Micromonosporaceae / Q000235:genetics / Q000378:metabolism; D048630:Polyketide Synthases / Q000235:genetics; D016133:Polymerase Chain Reaction; D013302:Streptomyces / Q000235:genetics / Q000378:metabolism
chemical_list: D062365:Aminobenzoates; D001688:Biological Products; D062385:Hydroxybenzoates; D047029:Lactams, Macrocyclic; C031509:3-amino-5-hydroxybenzoic acid; D048630:Polyketide Synthases; C111160:3-amino-5-hydroxybenzoic acid synthase; D006836:Hydro-Lyases