Easom Catherine A, Clarke David J
Department of Microbiology, University College Cork, Ireland.
BMC Microbiol. 2008 Oct 3;8:168. doi: 10.1186/1471-2180-8-168.
Photorhabdus are motile members of the family Enterobactericeae that are pathogenic to insect larvae whilst also maintaining a mutualistic interaction with entomophagous nematodes of the family Heterorhabditiae. The interactions between Photorhabdus and its hosts are thought to be an obligate part of the bacteria's life-cycle in the environment. Motility often plays a key role in mediating bacteria-host interactions and, in this study, we were interested in characterising the role of motility in the Photorhabdus-nematode-insect tripartite association.
We constructed deletion mutants of flgG (blocking flagella production) and motAB (blocking flagella rotation) in P. luminescens TT01. Using these mutants we show that both the DeltaflgG and DeltamotAB mutants are equally as good as the wild-type (WT) bacteria in killing insects and supporting nematode growth and development suggesting that flagella production and motility are not required for pathogenicity or mutualism. However we show that the production of flagella is associated with a significant metabolic cost during growth on agar plates suggesting that, although not required for pathogenicity or mutualism, there must be a strong selective pressure to retain flagella production (and motility) during the interactions between Photorhabdus and its different hosts. To this end we show that both the DeltaflgG and DeltamotAB mutants are out-competed by WT Photorhabdus during prolonged incubation in the insect revealing that motile bacteria do have a fitness advantage during colonisation of the insect larva.
This is the first report of a role for motility in Photorhabdus and we show that, although not required for either pathogenicity or mutualism, motility does contribute to the competitive fitness of Photorhabdus during infection of the insect (and, to a lesser extent, the nematode). This adaptive function is similar to the role ascribed to motility in mammalian pathogens such as uropathogenic Escherichia coli (UPEC). Therefore, in addition to describing a role for motility in Photorhabdus, this study reinforces the relevance and utility of this bacterium as a model for studying bacteria-host interactions.
发光杆菌属是肠杆菌科的可运动成员，对昆虫幼虫具有致病性，同时还与异小杆线虫科的食虫线虫保持着共生关系。发光杆菌与其宿主之间的相互作用被认为是该细菌在环境中生命周期的一个必要组成部分。运动性通常在介导细菌与宿主的相互作用中起关键作用，在本研究中，我们感兴趣的是确定运动性在发光杆菌-线虫-昆虫三方关联中的作用。
我们构建了发光杆菌TT01中flgG（阻断鞭毛产生）和motAB（阻断鞭毛旋转）的缺失突变体。利用这些突变体，我们发现ΔflgG和ΔmotAB突变体在杀死昆虫以及支持线虫生长和发育方面与野生型（WT）细菌一样好，这表明致病性或共生关系并不需要鞭毛产生和运动性。然而，我们表明在琼脂平板上生长期间，鞭毛的产生与显著的代谢成本相关，这表明，尽管致病性或共生关系不需要鞭毛产生，但在发光杆菌与其不同宿主之间的相互作用过程中，必然存在强烈的选择压力来保留鞭毛产生（和运动性）。为此，我们表明在昆虫中长时间孵育期间，ΔflgG和ΔmotAB突变体都被WT发光杆菌竞争淘汰，这表明运动性细菌在昆虫幼虫定殖期间确实具有适应性优势。
这是关于运动性在发光杆菌中作用的首次报道，我们表明，尽管致病性或共生关系都不需要运动性，但运动性确实有助于发光杆菌在感染昆虫期间（以及在较小程度上感染线虫期间）的竞争适应性。这种适应性功能类似于在哺乳动物病原体如尿路致病性大肠杆菌（UPEC）中归因于运动性的作用。因此，除了描述运动性在发光杆菌中的作用外，本研究还强化了这种细菌作为研究细菌-宿主相互作用模型的相关性和实用性。
