title: Phylogeny of HCN synthase-encoding hcnBC genes in biocontrol fluorescent pseudomonads and its relationship with host plant species and HCN synthesis ability.
abstract: Hydrogen cyanide (HCN) is a broad-spectrum antimicrobial compound involved in biological control of root diseases by many plant-associated fluorescent pseudomonads. The HCN synthase is encoded by three biosynthetic genes (hcnA, hcnB, and hcnC), but little is known about the diversity of these genes in fluorescent Pseudomonas spp. and in other bacteria. Here, the partial hcnBC sequence was determined for a worldwide collection of biocontrol fluorescent Pseudomonas spp. Phylogenies based on hcnBC and deduced protein sequences revealed four main bacterial groups, but topological incongruences were found between hcnBC and rrs-based phylogenies, suggesting past lateral transfer of hcnBC among saprophytic root-colonizing pseudomonads. Three of the four groups included isolates from different countries and host plants. Yet, these groups corresponded to distinct, ecologically-adapted populations of HCN-producing biocontrol fluorescent pseudomonads, as indicated by high hcnBC distinctness ratio values and the differences in production levels of HCN in vitro found between groups. This is in accordance with previous results on catabolic properties and biocontrol abilities of these strains. HCN synthase gene diversity may thus reflect the adaptive radiation of HCN+ biocontrol fluorescent pseudomonads. Positive correlations were found between HCN production in vitro and plant protection in the cucumber/Pythium ultimum and tomato/Fusarium oxysporum f. sp. radicis-lycopersici pathosystems.
authors.affiliation: Phytopathology Group, Institute of Plant Sciences, Swiss Federal Institute of Technology (ETH), CH-8092 Zürich, Switzerland.
authors.forename: Alban
authors.initials: A
authors.lastname: Ramette
authors.forename: Michele
authors.initials: M
authors.lastname: Frapolli
authors.forename: Geneviève
authors.initials: G
authors.lastname: Défago
authors.forename: Yvan
authors.initials: Y
authors.lastname: Moënne-Loccoz
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D006856:Hydrogen Cyanide / Q000378:metabolism; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics* / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D050891:Oxidoreductases Acting on CH-NH2 Group Donors; D010802:Phylogeny; D010944:Plants / Q000382:microbiology*; D011549:Pseudomonas / Q000145:classification / Q000201:enzymology / Q000235:genetics*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D009097:Multienzyme Complexes; D012336:RNA, Ribosomal, 16S; D006856:Hydrogen Cyanide; D010088:Oxidoreductases; D050891:Oxidoreductases Acting on CH-NH2 Group Donors; C112800:glycine dehydrogenase (cyanide-forming)