ABSTRACT

Acinetobacter baumannii is a pathogen of increasing clinical importance worldwide, especially given its ability to readily acquire resistance determinants. Motile strains of this bacterium can move by either or both of two types of motility: (i) twitching, driven by type IV pili, and (ii) surface-associated motility, an appendage-independent form of movement. A. baumannii strain MAR002 possesses both twitching and surface-associated motility. In this study, we isolated spontaneous rifampin-resistant mutants of strain MAR002 in which point mutations in the rpoB gene were identified that resulted in an altered motility pattern. Transcriptomic analysis of mutants lacking twitching, surface-associated motility, or both led to the identification of deregulated genes within each motility phenotype, based on their level of expression and their biological function. Investigations of the corresponding knockout mutants revealed several genes involved in the motility of A. baumannii strain MAR002, including two involved in twitching (encoding a minor pilin subunit and an RND [resistance nodulation division] component), one in surface-associated motility (encoding an amino acid permease), and eight in both (encoding RND and ABC components, the energy transducer TonB, the porin OprD, the T6SS component TagF, an IclR transcriptional regulator, a PQQ-dependent sugar dehydrogenase, and a putative pectate lyase). Virulence assays showed the reduced pathogenicity of mutants with impairments in both types of motility or in surface-associated motility alone. By contrast, the virulence of twitching-affected mutants was not affected. These results shed light on the key role of surface-associated motility and the limited role of twitching in the pathogenicity of A. baumannii.

摘要

鲍曼不动杆菌是一种在全球范围内具有越来越重要临床意义的病原体，特别是考虑到它能够容易地获得耐药性决定因素。这种细菌的运动菌株可以通过两种运动中的一种或两种运动：（i）由 IV 型菌毛驱动的抽搐，和（ii）表面相关运动，一种独立于附属物的运动形式。A. baumannii菌株 MAR002 具有抽搐和表面相关运动。在这项研究中，我们分离了 MAR002 菌株的自发利福平耐药突变体，其中rpoB中的点突变确定了导致运动模式改变的基因。基于它们的表达水平和它们的生物学功能，对缺乏抽搐、表面相关运动或两者的突变体的转录组学分析导致​​在每个运动表型中识别出失调的基因。对相应敲除突变体的研究揭示了几个与鲍曼不动杆菌运动有关的基因菌株 MAR002，包括两个参与抽搐（编码一个次要的菌毛蛋白亚基和一个 RND [抗性结瘤分裂] 成分），一个涉及表面相关运动（编码一种氨基酸通透酶），以及 8 个参与两者（编码 RND 和 ABC 成分，能量传感器 TonB、孔蛋白 OprD、T6SS 成分 TagF、IclR 转录调节剂、PQQ 依赖性糖脱氢酶和假定的果胶酸裂解酶）。毒力测定显示，两种运动或仅表面相关运动受损的突变体的致病性降低。相比之下，受抽搐影响的突变体的毒力没有受到影响。这些结果揭示了表面相关运动的关键作用以及抽搐在鲍曼不动杆菌致病性中的有限作用。