Department of Environmental Protection, Estación Experimental del Zaidín, CSIC, Granada, Spain.
Appl Environ Microbiol. 2012 Oct;78(19):6963-74. doi: 10.1128/AEM.00901-12. Epub 2012 Jul 27.
The stability of seven genomic islands of Pseudomonas putida KT2440 with predicted potential for mobilization was studied in bacterial populations associated with the rhizosphere of corn plants by multiplex PCR. DNA rearrangements were detected for only one of them (GI28), which was lost at high frequency. This genomic island of 39.4 kb, with 53 open reading frames, shows the characteristic organization of genes belonging to tailed phages. We present evidence indicating that it corresponds to the lysogenic state of a functional bacteriophage that we have designated Pspu28. Integrated and rarely excised forms of Pspu28 coexist in KT2440 populations. Pspu28 is self-transmissible, and an excisionase is essential for its removal from the bacterial chromosome. The excised Pspu28 forms a circular element that can integrate into the chromosome at a specific location, att sites containing a 17-bp direct repeat sequence. Excision/insertion of Pspu28 alters the promoter sequence and changes the expression level of PP_1531, which encodes a predicted arsenate reductase. Finally, we show that the presence of Pspu28 in the lysogenic state has a negative effect on bacterial fitness in the rhizosphere under conditions of intraspecific competition, thus explaining why clones having lost this mobile element are recovered from that environment.
通过多重 PCR 研究了与玉米植物根际相关的细菌群体中预测具有迁移潜力的 7 个假单胞菌 KT2440 基因组岛的稳定性。仅检测到其中一个（GI28）发生了 DNA 重排，该基因组岛高频丢失。这个 39.4kb 的基因组岛有 53 个开放阅读框，表现出属于长尾噬菌体的基因的特征组织。我们提供的证据表明，它对应于我们指定为 Pspu28 的功能性噬菌体的溶原状态。整合和很少切除的 Pspu28 形式共同存在于 KT2440 群体中。Pspu28 是自我传播的，切除酶对于从细菌染色体上切除它是必不可少的。切除的 Pspu28 形成一个圆形元件，可以在特定位置整合到染色体上，att 位点含有 17 个碱基对的直接重复序列。Pspu28 的切除/插入会改变启动子序列并改变 PP_1531 的表达水平，PP_1531 编码一种预测的砷酸盐还原酶。最后，我们表明，在种内竞争条件下，溶原状态下的 Pspu28 的存在对根际中的细菌适应性有负面影响，这解释了为什么从该环境中恢复失去这种可移动元件的克隆。
