Kucho Ken-Ichi, Han On, Yunoki Miki
Graduate School of Science and Engineering, Kagoshima University.
Faculty of Science, Kagoshima University.
Microbes Environ. 2025;40(1). doi: 10.1264/jsme2.ME24062.
Frankia spp. are multicellular actinobacteria with the ability to fix atmospheric dinitrogen (N). Frankia fixes N not only in the free-living state, but also in root-nodule symbioses with more than 200 plant species called actinorhizal plants. In the present study, we isolated mutants of the pyrE (orotate phosphoribosyltransferase) and pyrF (orotidine-5'-phosphate decarboxylase) genes in Frankia casuarinae strain CcI3 using gamma rays as a mutagen and systematically identified the types of mutations that occurred in these genes. pyrEF mutants were isolated as uracil auxotrophs using the antimetabolite 5-fluoroorotic acid. We elucidated the nucleotide sequences of the pyrEF genes in 32 uracil auxotrophs, and detected eight substitutions, 17 single-nucleotide deletions, and seven large insertions. Large insertions were insertion sequences (IS elements); four belonged to the IS4 family, two to the IS66 family, and one to the IS110 family. This is the first study to demonstrate the mobilization of IS elements in the Frankia genome.
弗兰克氏菌属是一类多细胞放线菌，具有固定大气中双氮（N）的能力。弗兰克氏菌不仅能在自由生活状态下固氮，还能与200多种被称为放线菌根植物的植物形成根瘤共生固氮。在本研究中，我们以γ射线作为诱变剂，分离出了木麻黄弗兰克氏菌CcI3菌株中pyrE（乳清酸磷酸核糖基转移酶）和pyrF（乳清苷-5'-磷酸脱羧酶）基因的突变体，并系统地鉴定了这些基因中发生的突变类型。利用抗代谢物5-氟乳清酸，将pyrEF突变体分离为尿嘧啶营养缺陷型。我们阐明了32个尿嘧啶营养缺陷型中pyrEF基因的核苷酸序列，检测到8个替换、17个单核苷酸缺失和7个大的插入。大的插入是插入序列（IS元件）；4个属于IS4家族，2个属于IS66家族，1个属于IS110家族。这是首次证明弗兰克氏菌基因组中IS元件的移动性的研究。
