title: Hydrogen cyanide synthesis and antifungal activity of the biocontrol strain  Pseudomonas fluorescens  In5 from Greenland is highly dependent on growth medium.
abstract: Hydrogen cyanide (HCN) is a secondary metabolite produced by many antagonistic  Pseudomonas  species. In the present study, the gene cluster encoding HCN synthesis in a newly isolated  Pseudomonas fluorescens  strain, In5, from South Greenland was investigated. Sequence analysis showed that the Greenlandic hcn gene cluster comprises a novel hcn cluster. Transposon mutagenesis of strain In5 resulted in mutants In5-2E1 and In5-1H7 with no production of HCN, and mutant In5-6B9 with reduced HCN synthesis. In mutant In5-2E1, the transposon was inserted into the hcnC gene; in mutant In5-1H7, the Tn5 insertion was found in a region upstream of a putative malate:quinone oxidoreductase gene (mqo); and in mutant In5-6B9, the transposon disrupted a probable enoyl-CoA hydratase/isomerase gene. In vitro inhibition experiments with In5 (wild type) and In5-2E1 (mutant) showed that in nitrogen-rich Luria-Bertani medium, strain In5 but not the hcn mutant In5-2E1 produced HCN and inhibited the growth of hyphae of  Rhizoctonia solani  and  Pythium aphanidermatum . In contrast, when cultivating the strains in the carbohydrate-rich potato dextrose medium, neither of the strains produced any HCN, and thus, they were unable to inhibit hyphal growth of fungi. These experiments strongly indicate that the synthesis of HCN is highly dependent on the growth medium used.
authors.affiliation: Department of Agriculture and Ecology, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
authors.forename: Charlotte Frydenlund
authors.initials: CF
authors.lastname: Michelsen
authors.forename: Peter
authors.initials: P
authors.lastname: Stougaard
mesh_terms: D000898:Antibiosis; D000935:Antifungal Agents / Q000378:metabolism; D001483:Base Sequence; D003470:Culture Media / Q000378:metabolism; D004746:Enoyl-CoA Hydratase / Q000235:genetics / Q000378:metabolism; D005658:Fungi / Q000187:drug effects / Q000254:growth & development; D006116:Greenland; D006856:Hydrogen Cyanide / Q000378:metabolism*; D008825:Miconazole / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D011551:Pseudomonas fluorescens / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*
chemical_list: D000935:Antifungal Agents; D003470:Culture Media; D006856:Hydrogen Cyanide; D008825:Miconazole; D004746:Enoyl-CoA Hydratase