McGregor Glenn B, Sendall Barbara C, Niiyama Yuko, Tuji Akihiro, Willis Anusuya
Queensland Department of Environment and Science, Brisbane, Australia.
Queensland Department of Health, Forensic and Scientific Services, Coopers Plains, Australia.
J Phycol. 2023 Apr;59(2):326-341. doi: 10.1111/jpy.13317. Epub 2023 Mar 9.
True branching is a facultative characteristic only known from two cyanobacteria in the Aphanizomenonaceae, Umezakia natans and Dolichospermum brachiatum. In both cases, its expression has been associated with environmental stress, and its practical use as a diacritical feature has been previously evaluated. In this study, we undertook further evaluation of the phylogeny of Umezakia natans and its relationship to Chrysosporum ovalisporum as a previous study suggested the two were potentially congeneric. We used combined morphological, phylogenetic, and phylogenomic approaches to determine their relatedness using new strains available from a broad geographic range. Phylogenetic analysis based on 16S rRNA gene sequences showed that Australian C. ovalisporum and Japanese U. natans strains clustered together with accessions of C. ovalisporum originating from Australia, Israel, and Spain, with high p-distance similarity values (99.5%-99.9%). Additionally, differences between the two species in the 16S-23S ITS region was low (0%-2.5%). The average nucleotide identity of the U. natans and C. ovalisporum strains was also high (ANI of > 99.5 and AF > 0.9) and supported a genus-level separation from Chrysosporum bergii (83 ANI between clusters). Furthermore, in culture, strains of both species grown in vitamin-free media showed facultative true branching, a feature not previously known in C. ovalisporum. Collectively, the results support unification of C. ovalisporum and U. natans according to the principle of priority as Umezakia ovalisporum.
真正的分支是一种兼性特征，仅在胶须藻科的两种蓝细菌中被发现，即纳氏胶须藻（Umezakia natans）和短枝束丝藻（Dolichospermum brachiatum）。在这两种情况下，其表达都与环境压力有关，并且其作为鉴别特征的实际用途此前已得到评估。在本研究中，我们对纳氏胶须藻的系统发育及其与卵形金孢藻（Chrysosporum ovalisporum）的关系进行了进一步评估，因为之前的一项研究表明这两者可能是同属的。我们使用形态学、系统发育学和系统基因组学相结合的方法，利用来自广泛地理范围的新菌株来确定它们之间的亲缘关系。基于16S rRNA基因序列的系统发育分析表明，澳大利亚的卵形金孢藻菌株和日本的纳氏胶须藻菌株与来自澳大利亚、以色列和西班牙的卵形金孢藻菌株聚集在一起，具有较高的p距离相似性值（99.5%-99.9%）。此外，这两个物种在16S-23S ITS区域的差异也很小（0%-2.5%）。纳氏胶须藻和卵形金孢藻菌株的平均核苷酸同一性也很高（ANI>99.5且AF>0.9），并支持将它们与伯格金孢藻（Chrysosporum bergii）在属级水平上区分开来（聚类之间的ANI为83）。此外，在培养过程中，两种物种的菌株在无维生素培养基中生长时都表现出兼性真正的分支，这是卵形金孢藻以前未知的特征。总体而言，这些结果支持根据优先权原则将卵形金孢藻和纳氏胶须藻统一为卵形胶须藻（Umezakia ovalisporum）。
