Aoyagi Kari L, Brooks Benjamin D, Bearden Scott W, Montenieri John A, Gage Kenneth L, Fisher Mark A
University of Utah Department of Pathology, 2100 JMRB, 15 North Medical Drive East, Salt Lake City, UT 84132, USA.
Division of Vector-Borne Diseases, Bacterial Diseases Branch, Centers for Disease Control and Prevention, 3156 Rampart Road, Fort Collins, CO 80521, USA.
Microbiology (Reading). 2015 Mar;161(Pt 3):628-38. doi: 10.1099/mic.0.000018. Epub 2014 Dec 22.
Yersinia pestis, the causative agent of plague, can be transmitted by fleas by two different mechanisms: by early-phase transmission (EPT), which occurs shortly after flea infection, or by blocked fleas following long-term infection. Efficient flea-borne transmission is predicated upon the ability of Y. pestis to be maintained within the flea. Signature-tagged mutagenesis (STM) was used to identify genes required for Y. pestis maintenance in a genuine plague vector, Xenopsylla cheopis. The STM screen identified seven mutants that displayed markedly reduced fitness in fleas after 4 days, the time during which EPT occurs. Two of the mutants contained insertions in genes encoding glucose 1-phosphate uridylyltransferase (galU) and UDP-4-amino-4-deoxy-l-arabinose-oxoglutarate aminotransferase (arnB), which are involved in the modification of lipid A with 4-amino-4-deoxy-l-arabinose (Ara4N) and resistance to cationic antimicrobial peptides (CAMPs). These Y. pestis mutants were more susceptible to the CAMPs cecropin A and polymyxin B, and produced lipid A lacking Ara4N modifications. Surprisingly, an in-frame deletion of arnB retained modest levels of CAMP resistance and Ara4N modification, indicating the presence of compensatory factors. It was determined that WecE, an aminotransferase involved in biosynthesis of enterobacterial common antigen, plays a novel role in Y. pestis Ara4N modification by partially offsetting the loss of arnB. These results indicated that mechanisms of Ara4N modification of lipid A are more complex than previously thought, and these modifications, as well as several factors yet to be elucidated, play an important role in early survival and transmission of Y. pestis in the flea vector.
鼠疫耶尔森菌是鼠疫的病原体，可通过跳蚤经两种不同机制传播：一是早期传播（EPT），发生在跳蚤感染后不久；二是长期感染后形成的堵塞型跳蚤传播。高效的跳蚤传播取决于鼠疫耶尔森菌在跳蚤体内存活的能力。利用签标签诱变（STM）技术，在真正的鼠疫传播媒介印鼠客蚤中鉴定出鼠疫耶尔森菌存活所需的基因。STM筛选鉴定出7个突变体，在4天后（即EPT发生的时间），这些突变体在跳蚤体内的适应性显著降低。其中两个突变体的编码葡萄糖1-磷酸尿苷转移酶（galU）和UDP-4-氨基-4-脱氧-L-阿拉伯糖-草酰谷氨酸氨基转移酶（arnB）的基因发生插入，这两种酶参与用4-氨基-4-脱氧-L-阿拉伯糖（Ara4N）修饰脂质A以及对阳离子抗菌肽（CAMP）的抗性。这些鼠疫耶尔森菌突变体对CAMP天蚕素A和多粘菌素B更敏感，且产生的脂质A缺乏Ara4N修饰。令人惊讶的是，arnB的框内缺失仍保留了一定水平的CAMP抗性和Ara4N修饰，表明存在补偿因子。已确定，参与肠杆菌共同抗原生物合成的氨基转移酶WecE通过部分抵消arnB的缺失，在鼠疫耶尔森菌Ara4N修饰中发挥新作用。这些结果表明，脂质A的Ara4N修饰机制比以前认为的更为复杂，这些修饰以及几个尚待阐明的因素，在鼠疫耶尔森菌在跳蚤媒介中的早期存活和传播中起重要作用。
