Department of Microbiology and Immunology, The University of British Columbia, Vancouver, BC, Canada.
Department of Plant Biology, University of California, Davis, Davis, CA, USA.
ISME J. 2019 Jun;13(6):1575-1588. doi: 10.1038/s41396-019-0372-5. Epub 2019 Feb 20.
Host-associated bacteria can have both beneficial and detrimental effects on host health. While some of the molecular mechanisms that determine these outcomes are known, little is known about the evolutionary histories of pathogenic or mutualistic lifestyles. Using the model plant Arabidopsis, we found that closely related strains within the Pseudomonas fluorescens species complex promote plant growth and occasionally cause disease. To elucidate the genetic basis of the transition between commensalism and pathogenesis, we developed a computational pipeline and identified genomic islands that correlate with outcomes for plant health. One island containing genes for lipopeptide biosynthesis and quorum-sensing is required for pathogenesis. Conservation of the quorum-sensing machinery in this island allows pathogenic strains to eavesdrop on quorum signals in the environment and coordinate pathogenic behavior. We found that genomic loci associated with both pathogenic and commensal lifestyles were convergently gained and lost in multiple lineages through homologous recombination, possibly constituting an early step in the differentiation of pathogenic and commensal lifestyles. Collectively this work provides novel insights into the evolution of commensal and pathogenic lifestyles within a single clade of host-associated bacteria.
宿主相关细菌对宿主健康既有有益的影响，也有有害的影响。虽然已经了解了一些决定这些结果的分子机制，但对于致病或共生生活方式的进化历史却知之甚少。我们使用模式植物拟南芥发现，荧光假单胞菌种复合体中的密切相关菌株可促进植物生长，偶尔也会导致疾病。为了阐明从共生到发病之间的遗传基础，我们开发了一种计算管道，并鉴定了与植物健康结果相关的基因组岛。一个包含脂肽生物合成和群体感应基因的岛是发病所必需的。该岛中群体感应机制的保守性允许致病菌株在环境中监听群体信号并协调致病行为。我们发现，与致病和共生生活方式相关的基因组位点通过同源重组在多个谱系中被趋同获得和丢失，这可能构成了致病和共生生活方式分化的早期步骤。总的来说，这项工作为宿主相关细菌的单一进化枝中的共生和致病生活方式的进化提供了新的见解。
