Selection of host specific genes in environmentally transmitted mutualism

描述（由申请人提供）：海鞘鱿鱼（软体动物：头足纲）和它们的共生弧菌之间的共生关系是一个实验可处理的模型，用于研究动物和细菌在各种相互作用水平（遗传学，生理学，种群生态学）上的关联进化。由于共生细菌每一代都在环境中传播给新的宿主，因此它提供了一个机会来解决自由生活的共生生态如何影响细菌-宿主相互作用的结构。细菌面临着潜在的相互冲突的选择压力，它们相互竞争，以在乌贼的皮脂光器官中定植和生存，但也在乌贼之外的环境中争夺稀缺的资源。在乌贼的定殖过程中，特定的fischeri弧菌比其他的fishcheri弧菌更有竞争力，而水和温度等非生物因素也会影响不同菌株的适合度。导致种内适应度变化的遗传因素尚未被阐明，可能影响环境中种内适应度的遗传因素也尚未被阐明。以下项目将研究仅在海水中高表达或仅在光器官中表达的基因如何促进细菌适应性。本提案是我实验室目前工作的延伸，并侧重于四个具体目标：

DESCRIPTION (provided by applicant): The mutualistic association between sepiolid squids (Mollusca: Cephalopoda) and their Vibrio symbionts is an experimentally tractable model to study the evolution of animal and bacterial associations at various levels of interaction (genetics, physiology, population ecology). Since symbiotic bacteria are environmentally transmitted to new hosts with every generation, it provides an opportunity to resolve how the ecology of the free-living symbiont affects the architecture of bacterial-host interactions. Bacteria encounter potentially conflicting selective pressures, competing with one another to colonize and persist in the sepiolid light organ, but also competing for scarce resources in the environment outside the squid. A hierarchy of colonization exists, where particular V. fischeri strains out-compete other V. fischeri strains for colonization of their native squid partner, and abiotic factors such as water and temperature can affect the fitness of different strains. Genetic factors that contribute to intra-strain variations in fitness have not been elucidated, and neither have the genetic factors that likely contribute to intra-strain fitness in the environment. The following project will examine how genes that are highly-expressed exclusively in sea water or expressed exclusively in the light organ contribute to bacterial fitness. The present proposal is an extension of the current work in my laboratory, and focuses on four specific goals: i) Characterize environmentally-relevant phenotypes of strains with null mutations in highly-expressed, variable genes. ii) Determine whether a mutant strain complemented with the wild-type operon from the same strain is fit for environmental persistence (free-living) than the same strain complemented with the operon from a different strain. iii) Examine whether symbiotic strains with specific variable loci complemented with the wild-type operon or gene from the same strain are fit for host colonization than the same strain complemented with the operon/gene from a different strain. iv) Measure whether symbiotic genes are found in pathogenicity islands through whole genome comparisons, and demonstrate positive selection of these genes compared to normal housekeeping genes.