Ogier Jean-Claude, Pagès Sylvie, Bisch Gaëlle, Chiapello Hélène, Médigue Claudine, Rouy Zoé, Teyssier Corinne, Vincent Stéphanie, Tailliez Patrick, Givaudan Alain, Gaudriault Sophie
INRA, UMR Diversité, Génomes et Interactions Microorganismes-Insectes (DGIMI), Montpellier, FranceUniversité Montpellier 2, UMR Diversité, Génomes et Interactions Microorganismes-Insectes (DGIMI), France.
INRA Toulouse Midi-Pyrénées, Unité MIA-T, Chemin de Borde Rouge, Castanet-Tolosan, France.
Genome Biol Evol. 2014 Jun 5;6(6):1495-513. doi: 10.1093/gbe/evu119.
Bacteria of the genus Xenorhabdus are symbionts of soil entomopathogenic nematodes of the genus Steinernema. This symbiotic association constitutes an insecticidal complex active against a wide range of insect pests. Unlike other Xenorhabdus species, Xenorhabdus poinarii is avirulent when injected into insects in the absence of its nematode host. We sequenced the genome of the X. poinarii strain G6 and the closely related but virulent X. doucetiae strain FRM16. G6 had a smaller genome (500-700 kb smaller) than virulent Xenorhabdus strains and lacked genes encoding potential virulence factors (hemolysins, type 5 secretion systems, enzymes involved in the synthesis of secondary metabolites, and toxin-antitoxin systems). The genomes of all the X. poinarii strains analyzed here had a similar small size. We did not observe the accumulation of pseudogenes, insertion sequences or decrease in coding density usually seen as a sign of genomic erosion driven by genetic drift in host-adapted bacteria. Instead, genome reduction of X. poinarii seems to have been mediated by the excision of genomic blocks from the flexible genome, as reported for the genomes of attenuated free pathogenic bacteria and some facultative mutualistic bacteria growing exclusively within hosts. This evolutionary pathway probably reflects the adaptation of X. poinarii to specific host.
嗜线虫致病杆菌属细菌是斯氏线虫属土壤昆虫病原线虫的共生菌。这种共生关系构成了一种对多种害虫具有活性的杀虫复合体。与其他嗜线虫致病杆菌属物种不同，在没有其线虫宿主的情况下将嗜线虫致病杆菌注射到昆虫体内时，波氏嗜线虫致病杆菌是无毒的。我们对波氏嗜线虫致病杆菌G6菌株和密切相关但有毒的杜氏嗜线虫致病杆菌FRM16菌株的基因组进行了测序。G6的基因组比有毒的嗜线虫致病杆菌菌株小（小500 - 700 kb），并且缺乏编码潜在毒力因子（溶血素、5型分泌系统、参与次生代谢物合成的酶以及毒素 - 抗毒素系统）的基因。这里分析的所有波氏嗜线虫致病杆菌菌株的基因组大小都相似。我们没有观察到假基因的积累、插入序列或编码密度的降低，而这些通常被视为宿主适应细菌中由遗传漂变驱动的基因组侵蚀的迹象。相反，波氏嗜线虫致病杆菌的基因组减少似乎是由从灵活基因组中切除基因组块介导的，这与减毒的自由致病细菌和一些仅在宿主体内生长的兼性互利细菌的基因组情况相同。这种进化途径可能反映了波氏嗜线虫致病杆菌对特定宿主的适应性。
