A robust species tree for the alphaproteobacteria.

Area of Science:

• Microbiology
• Evolutionary Biology
• Genomics

Background:

• The evolutionary history and precise branching order of alphaproteobacterial orders remain debated.
• The origin of mitochondria within alphaproteobacteria, specifically Rickettsiales, is not universally agreed upon.

Purpose of the Study:

• To establish a robust phylogenetic tree for 72 alphaproteobacterial species.
• To clarify the evolutionary relationships among alphaproteobacterial orders and families.
• To investigate the placement of the mitochondrial ancestor within the alphaproteobacterial phylogeny.

Main Methods:

• Phylogenetic analysis using a concatenated alignment of 104 protein families from 72 alphaproteobacterial species.
• Construction of a species tree to infer evolutionary relationships.

Main Results:

• The study confirmed the coherence of four out of five major alphaproteobacterial orders.
• Rickettsiales, Rhodospirillales, and Sphingomonadales were identified as the three earliest-branching orders.
• The mitochondrial ancestor was placed within Rickettsiales, sister to Anaplasmataceae and Rickettsiaceae, with Pelagibacter forming the outgroup.

Conclusions:

• The phylogenetic framework supports Rickettsiales as the earliest diverging order and provides strong evidence for mitochondrial origin within this group.
• The study highlights taxonomic uncertainties, such as the placement of Hyphomonadaceae and the Caulobacterales group.
• Pelagibacter serves as a valuable outgroup for future studies on mitochondrial and eukaryotic gene evolution.