Evolution of virulence in Photorhabdus spp., entomopathogenic nematode symbionts

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• 作者：Dana Blackburn ; ^{blackbud84@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Perry L. Wood Jr. ^{pwood@byu.edu" class="auth_mail" title="E-mail the corresponding author} ; Travis J. Burk¹ ; ^{tburk034@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Burke Crawford ^{burkecrawford@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Sarah M. Wright ^{sarahmwright1@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Byron J. Adams ^{byron_adams@byu.edu" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Entomopathogenic nematode ; Phylogeny ; Ancestral character reconstruction
• 刊名：Systematic and Applied Microbiology
• 出版年：2016
• 出版时间：May 2016
• 年：2016
• 卷：39
• 期：3
• 页码：173-179
• 全文大小：960 K

文摘

Photorhabdus is a genus of Gram-negative bacteria belonging to the Enterobacteriaceae family. In addition to forming a mutualistic relationship with the Heterorhabditidae family of nematodes, these bacteria are the causal agent of insect mortality during nematode infection, and are commonly used as biocontrol agents against pest insects in managed ecosystems. There are three described species of Photorhabdus; Photorhabdus luminescens and Photorhabdus temperata, which are strictly entomopathogens, and Photorhabdus asymbiotica, which has been isolated from wound infections in humans. While there has been extensive research on its virulence mechanisms, the evolution of virulence in Photorhabdus has not previously been investigated within a phylogenetic context. To investigate how virulence has evolved in this genus, we first reconstructed the phylogenetic relationships among 18 strains representing each of the main taxonomic lineages in the genus. Bacterial cells were injected into Galleria mellonella and Tenebrio molitor larvae, and the LT₅₀ was calculated for each strain. These values were mapped onto the phylogeny using ancestral character reconstruction methods. With few exceptions, we found that the general trend of Photorhabdus evolution is one of increasing virulence. We also explored the relationship between virulence and Photorhabdus cell types and growth rates. Although we found no correlation between cell type and virulence, there was a strong correlation between virulence and growth rates in T. molitor. A better understanding of the origin and maintenance of virulence in this bacterium will aid in unraveling the mechanisms of the Heterorhabditis-Photorhabdus complex, resulting in the selection of more effective nematode-bacterium complexes for biocontrol.