Kewalo Marine Laboratory, University of Hawaii-Manoa, Honolulu, HI, USA.
ISME J. 2019 Mar;13(3):698-706. doi: 10.1038/s41396-018-0305-8. Epub 2018 Oct 23.
Strain diversity, while now recognized as a key driver underlying partner dynamics in symbioses, is usually difficult to experimentally manipulate and image in hosts with complex microbiota. To address this problem, we have used the luminous marine bacterium Vibrio fischeri, which establishes a symbiosis within the crypts of the nascent light organ of the squid Euprymna scolopes. Competition assays in newly hatched juvenile squid have shown that symbiotic V. fischeri are either niche-sharing "S strains", which share the light organ when co-inoculated with other S strains, or niche-dominant "D strains", which are typically found alone in the light organ after a co-colonization. To understand this D strain advantage, we determined the minimum time that different V. fischeri strains needed to initiate colonization and used confocal microscopy to localize the symbionts along their infection track. Further, we determined whether symbiont-induced host morphogenic events also occurred earlier during a D strain colonization. We conclude that D strains colonized more quickly than S strains. Nevertheless, light-organ populations in field-caught adult squid often contain both D and S strains. We determined experimentally that this symbiont population heterogeneity might be achieved in nature by a serial encounter of different strains in the environment.
菌株多样性虽然现在被认为是共生体中伙伴动态的关键驱动因素，但通常难以在具有复杂微生物群的宿主中进行实验操作和成像。为了解决这个问题，我们使用了发光海洋细菌 Vibrio fischeri，它在鱿鱼 Euprymna scolopes 新生光器官的crypt 中建立共生关系。在新孵化的幼年鱿鱼中的竞争实验表明，共生的 V. fischeri 要么是共享生态位的“S 菌株”，当与其他 S 菌株共同接种时，它们会共享光器官，要么是占据主导地位的“D 菌株”，它们通常在共同定植后独自存在于光器官中。为了了解这种 D 菌株优势，我们确定了不同 V. fischeri 菌株需要启动定植的最短时间，并使用共聚焦显微镜来定位共生体沿着它们的感染轨迹。此外，我们还确定了在 D 菌株定植期间，宿主形态发生事件是否也更早发生。我们得出结论，D 菌株比 S 菌株定植得更快。然而，在野外捕获的成年鱿鱼的光器官种群中经常同时含有 D 和 S 菌株。我们通过在环境中对不同菌株的连续接触实验确定，这种共生体种群异质性可能在自然界中实现。
