Comparative proteome analysis of Acidaminococcus intestini supports a relationship between outer membrane biogenesis in Negativicutes and Proteobacteria

The presence of bona fide outer membranes in members of the class Negativicutes is anomalous as phylogenetic analyses place this class within the phylum Firmicutes. To explore the relationships of a representative member of Negativicutes, we have performed a whole proteome BLAST analysis of Acidaminococcus intestini, which indicates that a substantial proportion (7 %) of the A. intestini proteome is closely related to sequences from members of the phylum Proteobacteria. In addition, we have identified key proteins involved in outer membrane biogenesis in A. intestini. This work highlights the need for further studies to define the relationships and evolutionary history of the Negativicutes.