Leclerc Laurene, Mattick John, Burns Brendan P, Sassera Davide, Hotopp Julie Dunning, Lo Nathan
F22 Life, Earth and Environmental Sciences Building, School of Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, Australia.
E26 Biological Sciences Building, School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
FEMS Microbiol Ecol. 2024 Nov 23;100(12). doi: 10.1093/femsec/fiae133.
Ticks are important vectors of bacterial, viral, and protozoan pathogens of humans and animals worldwide. Candidatus Midichloria mitochondrii is a highly abundant bacterial endosymbiont found in many tick species, including two medically important ticks respectively found in Europe and Australia, Ixodes ricinus and Ixodes holocyclus. The present study aimed to determine the symbiont's biological role by identifying lateral gene transfer (LGT) events, characterizing the transcriptome, and performing differential expression analyses. Metatranscriptomic data revealed that M. mitochondrii species in I. ricinus and I. holocyclus were equipped with the metabolic potential and were actively transcribing the genes for several important roles including heme, biotin and folate synthesis, oxidative stress response, osmotic regulation, and ATP production in microaerobic conditions. Differential expression analyses additionally showed an upregulation in stringent response and DNA repair genes in M. mitochondrii of I. holocyclus nymphs compared to adults. Low rates of differential expression suggest the symbiont may lack global gene regulation, as observed in other endosymbionts. Moreover, the identification of an LGT event and the proposed specialization of the M. mitochondrii strains, mIxholo1 and mIxholo2, for different I. holocyclus life stages highlight the complex interactions between M. mitochondrii and their tick hosts.
蜱是全球人类和动物的细菌、病毒及原生动物病原体的重要传播媒介。“嗜线粒体中绿菌（暂定名）”是一种在许多蜱种中大量存在的细菌内共生体，包括分别在欧洲和澳大利亚发现的两种具有医学重要性的蜱，即蓖麻硬蜱和全环硬蜱。本研究旨在通过识别横向基因转移（LGT）事件、表征转录组并进行差异表达分析来确定该共生体的生物学作用。宏转录组数据显示，蓖麻硬蜱和全环硬蜱中的嗜线粒体中绿菌具有代谢潜力，并正在积极转录多个重要作用的基因，包括血红素、生物素和叶酸合成、氧化应激反应、渗透调节以及在微需氧条件下产生ATP。差异表达分析还表明，与成虫相比，全环硬蜱若虫的嗜线粒体中绿菌的严谨反应和DNA修复基因上调。低差异表达率表明该共生体可能缺乏全局基因调控，这与其他内共生体的情况一致。此外，LGT事件的识别以及嗜线粒体中绿菌菌株mIxholo1和mIxholo2针对全环硬蜱不同生命阶段的拟议特化突出了嗜线粒体中绿菌与其蜱宿主之间复杂的相互作用。
