Millikan Deborah S, Ruby Edward G
Pacific Biomedical Research Center, University of Hawaii, Honolulu, Hawaii 96813, USA.
Appl Environ Microbiol. 2002 May;68(5):2519-28. doi: 10.1128/AEM.68.5.2519-2528.2002.
Motility is required for Vibrio fischeri cells to interact with and specifically colonize the light-emitting organ of their host, the squid Euprymna scolopes. To investigate the influence of motility on the expression of the symbiotic phenotype, we isolated mutants of the squid symbiont V. fischeri ES114 that had altered migration abilities. Spontaneous hyperswimmer (HS) mutants, which migrated more rapidly in soft agar and were hyperflagellated relative to the wild type, were isolated and grouped into three phenotypic classes. All of the HS strains tested, regardless of class, were delayed in symbiosis initiation. This result suggested that the hypermotile phenotype alone contributes to an inability to colonize squid normally. Class III HS strains showed the greatest colonization defect: they colonized squid to a level that was only 0.1 to 10% that achieved by ES114. In addition, class III strains were defective in two capabilities, hemagglutination and luminescence, that have been previously described as colonization factors in V. fischeri. Class II and III mutants also share a mucoid colony morphology; however, class II mutants can colonize E. scolopes to a level that was 40% of that achieved by ES114. Thus, the mucoid phenotype alone does not contribute to the greater defect exhibited by class III strains. When squid were exposed to ES114 and any one of the HS mutant strains as a coinoculation, the parent strain dominated the resulting symbiotic light-organ population. To further investigate the colonization defects of the HS strains, we used confocal laser-scanning microscopy to visualize V. fischeri cells in their initial interaction with E. scolopes tissue. Compared to ES114, HS strains from all three classes were delayed in two behaviors involved in colonization: (i) aggregation on host-derived mucus structures and (ii) migration to the crypts. These results suggest that, while motility is required to initiate colonization, the presence of multiple flagella may actually interfere with normal aggregation and attachment behavior. Furthermore, the pleiotropic nature of class III HS strains provides evidence that motility is coregulated with other symbiotic determinants in V. fischeri.
费氏弧菌细胞与宿主夏威夷短尾鱿鱼的发光器官相互作用并特异性定殖需要运动性。为了研究运动性对共生表型表达的影响，我们分离了鱿鱼共生菌费氏弧菌ES114的迁移能力发生改变的突变体。分离出了自发的超游动（HS）突变体，它们在软琼脂中迁移得更快，并且相对于野生型具有更多的鞭毛，并将其分为三个表型类别。所有测试的HS菌株，无论类别如何，共生起始都延迟了。这一结果表明，仅超运动表型就导致无法正常定殖鱿鱼。III类HS菌株表现出最大的定殖缺陷：它们定殖鱿鱼的水平仅为ES114达到水平的0.1%至10%。此外，III类菌株在两种能力上存在缺陷，即血细胞凝集和发光，这两种能力先前已被描述为费氏弧菌中的定殖因子。II类和III类突变体也具有黏液状菌落形态；然而，II类突变体可以定殖夏威夷短尾鱿鱼，定殖水平为ES114达到水平的40%。因此，仅黏液状表型并不会导致III类菌株表现出更大的缺陷。当鱿鱼同时接种ES114和任何一种HS突变菌株时，亲本菌株在最终的共生发光器官群体中占主导地位。为了进一步研究HS菌株的定殖缺陷，我们使用共聚焦激光扫描显微镜观察费氏弧菌细胞与夏威夷短尾鱿鱼组织的初始相互作用。与ES114相比，所有三个类别的HS菌株在定殖所涉及的两种行为上都延迟了：（i）在宿主来源的黏液结构上聚集和（ii）迁移到隐窝。这些结果表明，虽然运动性是定殖起始所必需的，但多个鞭毛的存在实际上可能会干扰正常的聚集和附着行为。此外，III类HS菌株的多效性性质提供了证据，表明运动性与费氏弧菌中的其他共生决定因素共同调节。
