Penyalver Ramón, Oger Phil M, Su Shengchang, Alvarez Belén, Salcedo Carmina I, López María M, Farrand Stephen K
Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Mol Plant Microbe Interact. 2009 Jun;22(6):713-24. doi: 10.1094/MPMI-22-6-0713.
Agrobacterium radiobacter K84 is a commercial agent used worldwide to control crown gall disease caused by pathogenic isolates of A. tumefaciens. More than 2,000 transposon insertion derivatives of strain K84 were screened by a standardized greenhouse bioassay to identify mutants defective in biocontrol. Three mutants affected in biocontrol properties were identified. All three mutants displayed normal levels of attachment to tomato seed and root colonization. One of these mutants, M19-164, exhibited partial biocontrol and did not produce detectable levels of agrocin 84. In this mutant, the transposon is located in the agn locus of pAgK84, which codes for agrocin 84 biosynthesis. The second mutant, M19-158, also exhibited partial biocontrol and produced reduced amounts of agrocin 84 as a result of a mutation in a chromosomal gene of unknown function. The third mutant, M9-22, failed to biocontrol, was impaired in both growth in minimal medium and siderophore production, and failed to produce detectable levels of agrocin 84. The chromosomal gene ahcY, which encodes S-adenosyl-l-homocysteine hydrolase, was disrupted in this mutant. Expression of a functional copy of ahcY in M9-22 restored all of the altered phenotypes. The fact that all identified biocontrol mutants exhibited a partial or total defect in production of agrocin 84 indicates that this antibiotic is required for optimum biocontrol. This study also identified two chromosomally encoded genes required for agrocin 84 production. That a mutation in ahcY abolishes biocontrol suggests that the intracellular ratio of S-adenosyl-l-methionine to S-adenosyl-l-homocysteine is an important factor for agrocin 84 biosynthesis. Finally, we demonstrate that the ahcY gene in strain K84 is also required for optimal growth as well as for antibiotic production and biocontrol of crown gall disease.
放射土壤杆菌K84是一种在全球范围内用于防治由根癌土壤杆菌致病菌株引起的冠瘿病的商业制剂。通过标准化温室生物测定法对K84菌株的2000多个转座子插入衍生物进行了筛选，以鉴定生物防治缺陷型突变体。鉴定出三个生物防治特性受影响的突变体。这三个突变体在与番茄种子的附着和根部定殖水平上均表现正常。其中一个突变体M19 - 164表现出部分生物防治能力，且未产生可检测水平的农杆素84。在这个突变体中，转座子位于pAgK84的agn基因座中，该基因座编码农杆素84的生物合成。第二个突变体M19 - 158也表现出部分生物防治能力，由于一个功能未知的染色体基因突变，其农杆素84产量降低。第三个突变体M9 - 22无法进行生物防治，在基本培养基中的生长和铁载体产生均受损，且未产生可检测水平的农杆素84。该突变体中编码S - 腺苷 - L - 高半胱氨酸水解酶的染色体基因ahcY被破坏。在M9 - 22中表达功能性ahcY拷贝可恢复所有改变的表型。所有鉴定出的生物防治突变体在农杆素84产生方面表现出部分或完全缺陷，这一事实表明这种抗生素是最佳生物防治所必需的。本研究还鉴定出农杆素84产生所需的两个染色体编码基因。ahcY基因突变消除生物防治能力表明，S - 腺苷 - L - 甲硫氨酸与S - 腺苷 - L - 高半胱氨酸的细胞内比例是农杆素84生物合成的重要因素。最后，我们证明K84菌株中的ahcY基因对于最佳生长以及抗生素产生和冠瘿病的生物防治也是必需的。
