Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, KL Ledeganckstraat 35, B-9000 Ghent, Belgium.
Syst Appl Microbiol. 2013 Sep;36(6):426-35. doi: 10.1016/j.syapm.2013.04.005. Epub 2013 Jun 12.
Clavibacter michiganensis subsp. michiganensis (Cmm) is a seed-transmitted, quarantine pathogen which causes bacterial wilt and canker of tomato. Despite efforts to prevent seed contamination, new introductions are regularly detected, associated with new regions of tomato seed production. It seems as if the expanding diversity of Cmm also challenges the limited host range. Clavibacter-like isolates from tomato seed are phenotypically similar to Cmm in the common diagnostic semi-selective media and are identified as Cmm in the customary tests but are not pathogenic to tomato. In our first study four representatives formed a separate cluster in gyrB sequence analysis and in MALDI-TOF MS. Their presence on seed prevents clear judgment on the health status of tomato seeds. As their nature and function are unclear we aimed to investigate and compare them to Cmm. Twenty strains described as Clavibacter-like isolated from tomato seed and not pathogenic to tomato plantlets were selected. Leaf spots, wilting or cankers were not induced after local or systemic inoculation. Tomato stems were not colonized nor was there evidence of survival in tomato stems. Total DNA-DNA hybridization and sequence analysis of gyrB and dnaA proved that they belong to the Cm species but can be unambiguously separated from Cmm. Some of the genes encoding virulence determinants in Cmm strains were also detected in some of the non-pathogenic isolates. Moreover, Cmm strains formed a coherent group, while non-pathogenic Cm strains were heterogenic. The latter was confirmed by BOX-PCR. We speculate that tomato seeds likely represent a larger reservoir of unexplored Clavibacter diversity.
菜椒密执安棒杆菌亚种密执安ensis（Cmm）是一种种子传播的检疫性病原体，可引起番茄细菌性萎蔫和溃疡。尽管努力防止种子污染，但仍定期发现新的引入物，与番茄种子生产的新地区有关。似乎 Cmm 的多样性不断扩大也对有限的宿主范围构成了挑战。从番茄种子中分离出来的类棒杆菌在常见的诊断半选择性培养基中的表型与 Cmm 相似，在常规测试中被鉴定为 Cmm，但对番茄没有致病性。在我们的第一项研究中，四个代表在gyrB 序列分析和 MALDI-TOF MS 中形成了一个单独的聚类。它们在种子上的存在使得难以对番茄种子的健康状况做出明确判断。由于它们的性质和功能尚不清楚，我们旨在对它们进行调查并与 Cmm 进行比较。选择了 20 株被描述为从番茄种子中分离出来的类棒杆菌且对番茄幼苗没有致病性的菌株。局部或系统接种后不会诱导叶片斑点、萎蔫或溃疡。番茄茎未被定植，也没有证据表明在番茄茎中存活。gyrB 和 dnaA 的全 DNA-DNA 杂交和序列分析证明它们属于 Cm 种，但可以与 Cmm 明确区分开来。在一些非致病性分离株中也检测到了 Cmm 菌株中编码毒力决定因子的一些基因。此外，Cmm 菌株形成了一个连贯的群体，而非致病性 Cm 菌株则具有异质性。后者通过 BOX-PCR 得到了证实。我们推测，番茄种子可能代表了一个更大的尚未探索的棒杆菌多样性库。
