Williams Kelly P, Sobral Bruno W, Dickerman Allan W
Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
J Bacteriol. 2007 Jul;189(13):4578-86. doi: 10.1128/JB.00269-07. Epub 2007 May 4.
The branching order and coherence of the alphaproteobacterial orders have not been well established, and not all studies have agreed that mitochondria arose from within the Rickettsiales. A species tree for 72 alphaproteobacteria was produced from a concatenation of alignments for 104 well-behaved protein families. Coherence was upheld for four of the five orders with current standing that were represented here by more than one species. However, the family Hyphomonadaceae was split from the other Rhodobacterales, forming an expanded group with Caulobacterales that also included Parvularcula. The three earliest-branching alphaproteobacterial orders were the Rickettsiales, followed by the Rhodospirillales and then the Sphingomonadales. The principal uncertainty is whether the expanded Caulobacterales group is more closely associated with the Rhodobacterales or the Rhizobiales. The mitochondrial branch was placed within the Rickettsiales as a sister to the combined Anaplasmataceae and Rickettsiaceae, all subtended by the Pelagibacter branch. Pelagibacter genes will serve as useful additions to the bacterial outgroup in future evolutionary studies of mitochondrial genes, including those that have transferred to the eukaryotic nucleus.
α-变形菌纲各目之间的分支顺序和连贯性尚未完全确定，并非所有研究都认同线粒体起源于立克次氏体目。通过对104个表现良好的蛋白质家族的比对结果进行拼接，构建了包含72种α-变形菌的物种树。在这里由多个物种代表的当前现存的五个目中，有四个目保持了连贯性。然而，生丝微菌科与其他红杆菌目分开，与柄杆菌目形成了一个扩展的类群，该类群还包括微小杆菌属。α-变形菌纲最早分支的三个目是立克次氏体目，其次是红螺菌目，然后是鞘脂单胞菌目。主要的不确定性在于，扩展后的柄杆菌目类群与红杆菌目还是根瘤菌目关系更为密切。线粒体分支位于立克次氏体目内，是嗜吞噬细胞无形体科和立克次体科合并后的姊妹分支，所有这些都以浮霉菌分支为支撑。在未来线粒体基因的进化研究中，包括那些已转移到真核细胞核中的基因，浮霉菌基因将作为细菌外群的有用补充。
