Location: Horticultural Crops ResearchTitle: Genome sequencing and transposon mutagenesis of Burkholderia seminalis TC3.4.2R3 identify genes contributing to suppression of orchid necrosis caused by B. gladioli
|ARAUJO, WELINGTON - Universidade De Sao Paulo|
|CREASON, ALLISON - Oregon State University|
|MANO, EMY - Universidade De Sao Paulo|
|CAMARGO-NEVES, ALINE - Universidade De Sao Paulo|
|MINAMI, SONIA - Universidade De Sao Paulo|
|CHANG, JEFF - Oregon State University|
|LOPER, JOYCE - Former ARS Employee|
Submitted to: Molecular Plant Microbe International Symposium
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2016
Publication Date: 6/1/2016
Citation: Araujo, W.L., Creason, A., Mano, E.T., Camargo-Neves, A.A., Minami, S.N., Chang, J.H., Loper, J.E. 2016. Genome sequencing and transposon mutagenesis of Burkholderia seminalis TC3.4.2R3 identify genes contributing to suppression of orchid necrosis caused by B. gladioli. Molecular Plant Microbe International Symposium. 29(6):435-446. doi: 10.1094/MPMI-02-16-0047-R.
Interpretive Summary: Burkholderia gladioli causes a disease of orchids that is destructive to the large orchid industry of Brazil. There are very few ways to manage the disease caused by this bacterial pathogen in commercial orchid production in Brazil, so we investigated biological control as an option. We evaluated 36 naturally-occurring strains of Burkholderia spp. that do not cause orchid disease for biological control. When placed on orchid leaves, many of the strains could suppress the disease, which means that biological control could be a good way to manage this disease of orchids. We selected one effective strain for further study, and showed that it was successful in biological control of the disease on several orchid cultivars. We sequenced the genome of this effective strains and learned that the bacterium falls into a species called Burkholderia seminalis. We also identified several genes in B. seminalis that are necessary for biological control. This study identified naturally-occurring bacteria that could suppress an economically-important disease of orchid in Brazil. Unfortunately, it is unlikely that Burkholderia seminalis can be used for biological control because some strains of this bacterial species have been isolated from diseased lungs of cystic fibrosis patients and there is no certain way at present to ensure that this biological control strain does not have the capacity to cause disease of immuno-compromised humans.
Technical Abstract: Thirty six strains of Burkholderia spp. isolated from sugarcane were evaluated for biological control of leaf and pseudobulb necrosis of orchid caused by B. gladioli. Twenty nine of the sugarcane strains suppressed the disease in greenhouse assays. We generated a draft genomic sequence of one suppressive strain, B. seminalis TC3.4.2R3. The genome mapped to three replicons, two chromosomes and the plasmid pC3, with an estimated size of 7.67 Mb, and includes gene clusters for the biosynthesis of the antibiotic pyrrolnitrin, a rhamnolipid, the siderophores ornibactin and pyochelin, and IAA, as well as ethylene degradation via ACC deaminase. To gain insight into the mechanisms by which TC3.4.2R3 suppresses orchid necrosis, we generated a library of transposon mutants and screened 3,840 mutants for suppression of leaf necrosis. Twelve mutants that lacked biocontrol activity were selected and the transposon insertions were mapped to eight genes, all of which are on chromosome 1 of the genome. Of the eight genes essential to biocontrol that were identified in this genetic screen, one is in a wcb cluster that is related to synthesis of the cell capsule, a key determinant in bacterial-host interactions in other systems, and the other seven are highly conserved among Burkholderia spp.