ABSTRACT

Alphaproteobacteria share the propensity to intimately associate with plants and animals with other bacteria, but this propensity is so diffuse among their various phylogenetic groups that it has sustained the concept that proto-mitochondria originated within this bacterial class. Alphaproteobacteria include some of the most widespread and economically important prokaryotes, from agriculture to biotechnology and human health. Alphaproteobacteria are subdivided in an increasing number of orders and unclassified taxa. The basic phylogenetic tree of alphaproteobacteria was established in previous works, which had not considered Pelagibacter and its relatives. The taxonomic span or breadth of alphaproteobacteria, owing to programs designed to reduce the human bias in current genomic databases and the dramatic increase in metagenomic information on unclassified organisms. Within alphaproteobacteria, there are some of the most widely spread bacteria in Nature, namely Pelagibacter and Wolbachia. The former thrives in oceans, the latter inside insects and nematodes.