Xanthomonas citri pv. citri Genome sequencing and assembly

In 2015, backyard lime (Citrus spp.) trees in Texas exhibiting typical citrus canker symptoms were confirmed positive for Xanthomonas citri subsp. citri. This confirmation triggered a USDA regulatory response since the disease was absent from the state since 1940s. Rapid determination of the potential host range capacity of the strains was an important goal. The complete genomes of three strains isolated from infected trees in Texas were determined. Bioinformatic analyses indicated that the new strains were highly related to the Wellington (AW) strain group previously found in Florida, which are limited in host range to Mexican lime. However, all three Texas strains carried nearly identical and unusual large plasmids, significant fragments of which were found in contigs of unfinished genomes WGS database from some X. citri subsp citri, X. fuscans pv. fuscans and X. axonopodis pv. manihotis strains, which attack cassava plants. These plasmids contain a region of ca. 39 kB similar to Type 4 conjugational transfer genes, indicating potential for horizontal transfer. The predicted host range and pathogenicity effector repertoire was consistent with the observed AW phenotypic pathotype of these strains. No genes encoding additional potential effectors were identified on any the large plasmids.

2015年，德克萨斯州后院种植的典型柑橘类树（属柑橘属）表现出柑橘溃疡病的典型症状，经确认感染了黄单胞菌属柑橘种柑橘亚种。此次确诊触发了美国农业部（USDA）的监管反应，因为自20世纪40年代以来，该疾病已从该州消失。迅速确定这些菌株的潜在宿主范围能力成为一项重要目标。研究人员从德克萨斯州感染树木中分离出三个菌株，并确定了其完整基因组。生物信息学分析表明，这些新菌株与先前在佛罗里达州发现的惠灵顿（AW）菌株组高度相关，其宿主范围局限于墨西哥酸橙。然而，所有三个德克萨斯菌株均携带几乎完全相同且罕见的巨型质粒，其中部分重要片段在未完成基因组WGS数据库中的一些黄单胞菌属柑橘亚种、黄单胞菌属fuscans pv. fuscans和黄单胞菌属axonopodis pv. manihotis菌株的连续片段中被发现，这些菌株攻击木薯植物。这些质粒包含约39千碱基对的区域，类似于第4类接合转移基因，表明了潜在的横向转移能力。预测的宿主范围和致病性效应子谱系与这些菌株观察到的AW表型致病型一致。在任何巨型质粒上均未发现编码额外潜在效应子的基因。