An aerobic, Gram-stain-negative, motile and rod-shaped bacterial strain, designated as Z1-4T, was isolated from the phycosphere microbiota of marine dinoflagellate Alexandrium minutum that produces paralytic shellfish poisoning toxins. Phylogenetic analysis based on 16S rRNA gene sequences showed that the new isolate belongs to the genus Mesorhizobium, and it was closely related to Mesorhizobium waimense LMG 28228T and Mesorhizobium amorphae LMG 18977T with both 16S rRNA gene sequence similarities of 97.3%. The values of average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) relatedness between strain Z1-4T and its relatives are both well below the thresholds used for the delineation of a new species. A genome-based phylogenetic tree constructed by up-to-date bacterial core gene set (UBCG) indicates that strain Z1-4T forms an independent branch within the genus Mesorhizobium. The respiratory quinone of strain Z1-4T was Q-10. The major fatty acids were similar to other members of the genus Mesorhizobium containing the summed feature 8, C16:0, C19:0cycloω8c, C17:0 and summed feature 3. The polar lipids are phosphatidylmonomethylethanolamine, diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, an unidentified aminophospholipid, five glycolipids and seven unknown polar lipids. The DNA G + C content was determined to be 62.1 mol % based on its genomic sequence. Combined evidences based on the genotypic, chemotaxonomic and phenotypic characteristics clearly indicates that strain Z1-4T represents a novel species of the genus Mesorhizobium, for which the name Mesorhizobium alexandrii sp. nov. is proposed. The type strain is Z1-4T (= KCTC 72512T = CCTCC AB 2019101T).

中文翻译：

---

亚历山大藻 11月，从生产PSTs的海洋鞭毛藻亚历山大藻amtk4的藻圈微生物区系中分离出来。

从产生性麻痹性贝类中毒毒素的海洋鞭毛藻亚历山大藻的藻圈微生物中分离出了好氧，革兰氏阴性，能动和杆状的细菌菌株，称为Z1-4T。根据16S rRNA基因序列进行的系统进化分析表明，新分离株属于中生根瘤菌属，与威门中生根瘤菌LMG 28228T和紫穗兰中生菌LMG 18977T密切相关，两者的16S rRNA基因序列相似性为97.3％。Z1-4T菌株及其亲属之间的平均核苷酸同一性（ANI）和数字DNA-DNA杂交（dDDH）相关性的值均远低于用于描述新物种的阈值。由最新的细菌核心基因组（UBCG）构建的基于基因组的系统发育树表明，菌株Z1-4T在中生根瘤菌属中形成了一个独立的分支。Z1-4T菌株的呼吸醌为Q-10。主要脂肪酸与中生根瘤菌属的其他成员相似，包含加和特征8，C16：0，C19：0cycloω8c，C17：0和加总特征3。极性脂质为磷脂酰单甲基乙醇胺，二磷脂酰甘油，磷脂酰胆碱，磷脂酰乙醇胺，磷脂酰甘油，未鉴定的氨基磷脂，五个糖脂和七个未知的极性脂质。基于其基因组序列，确定DNA G + C含量为62.1mol％。基于基因型的综合证据，化学分类学和表型特征清楚地表明，菌株Z1-4T代表中生根瘤菌属的一个新物种，其名称为中生根瘤菌。十一月 被提议。类型菌株为Z1-4T（= KCTC 72512T = CCTCC AB 2019101T）。