Intracellular bacteria that are mainly transmitted maternally affect their arthropod hosts’ biology in various ways. One such effect is known as cytoplasmic incompatibility (CI), and three bacterial species are known to induce CI: Wolbachia, Cardinium hertigii, and a recently found alphaproteobacterial symbiont. To clarify the taxonomic status and provide the foundation for future studies to reveal CI mechanisms and other phenotypes, we investigated genetic and morphological properties of the third CI inducer that we have previously reported inducing CI in the coconut beetle Brontispa longissima. The draft genome of the bacteria was obtained from the oocytes of two isofemale lines of B. longissima infected with the bacteria: one from Japan (GL2) and the other from Vietnam (L5). Genome features of the symbionts (sGL2 and sL5) were highly similar, showing 1.3 Mb in size, 32.1% GC content, and 99.83% average nucleotide sequence. A phylogenetic study based on 43 universal and single-copy phylogenetic marker genes indicates that they formed a distinct clade in the family Anaplasmataceae. 16S rRNA gene sequences indicate that they are different from the closest known relatives, at least at the genus level. Therefore, we propose a new genus and species, “Candidatus Mesenet longicola”, for the symbionts of B. longissima. Morphological analyses showed that Ca. M. longicola is an intracellular bacterium that is ellipsoidal to rod-shaped and 0.94 ± 0.26 μm (mean ± SD) in length, and accumulated in the anterior part of the oocyte. Candidates for the Ca. M. longicola genes responsible for CI induction are also described.

主要通过母体传播的细胞内细菌以各种方式影响其节肢动物宿主的生物学。一种这样的效应被称为细胞质不相容性 (CI)，已知三种细菌物种会诱发 CI：沃尔巴克氏菌、Cardinium hertigii和最近发现的一种α-变形菌共生体。为了澄清分类地位并为未来研究揭示 CI 机制和其他表型奠定基础，我们调查了第三个 CI 诱导剂的遗传和形态学特性，我们之前报告过在椰子甲虫Brontispa longissima 中诱导 CI 。该细菌的基因组草图是从B. longissima的两个同种雌性系的卵母细胞中获得的感染了细菌：一个来自日本（GL2），另一个来自越南（L5）。共生体（sGL2 和 sL5）的基因组特征高度相似，大小为 1.3 Mb，GC 含量为 32.1%，平均核苷酸序列为 99.83%。基于 43 个通用和单拷贝系统发育标记基因的系统发育研究表明它们在无形体科中形成了一个独特的进化枝。16S rRNA 基因序列表明它们至少在属水平上与已知的最近亲属不同。因此，我们为B. longissima的共生体提出了一个新的属和种，“ Candidatus Mesenet longicola” 。形态学分析表明，Ca。M. longicola 是一种细胞内细菌，呈椭圆形至杆状，长度为 0.94 ± 0.26 μm（平均值 ± SD），并在卵母细胞的前部积聚。Ca的候选人。还描述了负责 CI 诱导的 M. longicola 基因。