A new α‐proteobacterial clade of Bdellovibrio‐like predators: implications for the mitochondrial endosymbiotic theory

Abstract

Bdellovibrio-and-like organisms (BALOs) are peculiar, ubiquitous, small-sized, highly motile Gram-negative bacteria that are obligatory predators of other bacteria. Typically, these predators invade the periplasm of their prey where they grow and replicate. To date, BALOs constitute two highly diverse families affiliated with the delta-proteobacteria class. In this study, Micavibrio spp., a BALO lineage of epibiotic predators, were isolated from soil. These bacteria attach to digest and grow at the expense of other prokaryotes, much like other BALOs. Multiple phylogenetic analyses based on six genes revealed that they formed a deep branch within the alpha-proteobacteria, not affiliated with any of the alpha-proteobacterial orders. The presence of BALOs deep among the alpha-proteobacteria suggests that their peculiar mode of parasitism maybe an ancestral character in this proteobacterial class. The origin of the mitochondrion from an alpha-proteobacterium endosymbiont is strongly supported by molecular phylogenies. Accumulating data suggest that the endosymbiont's host was also a prokaryote. As prokaryotes are unable to phagocytose, the means by which the endosymbiont gained access into its host remains mysterious. We here propose a scenario based on the BALO feeding-mode to hypothesize a mechanism at play at the origin of the mitochondrial endosymbiosis.

In and out: an analysis of epibiotic vs periplasmic bacterial predators

“…This, along with the examination of their genomic content and genome structure, suggests that epibiotic predation in BALO results from convergent evolution, and has evolved a number of times in unrelated taxa. Furthermore, M. aeruginosavorus represents a deep taxonomic branch in the a-proteobacteria with its closest relative within the SAR116 group, both forming a sister clade to the Rhodospirillales (Davidov et al, 2006;Wang et al, 2011). Because neither the SAR116 nor the Rhodospirillales contain any known predators, it is likely that M. aeruginosavorus evolved to be an epibiotic predator 'de novo', from an unidentified nonpredatory ancestor.…”

“…M. aeruginosavorus strain EPB was isolated from saline soil in Israel using Pseudomonas corrugata as prey (Davidov et al, 2006). The prey strains were cultured in PYE and NB, respectively.…”

Semiconductor Sequencing Reveals the Diversity of Bacterial Communities in an Amazonian Reservoir

“…The Δ-Proteobacteria represented approximately 4% of Proteobacteria and belonged predominantly to the class Bdellovibrionales. None of the sequences could be assigned to a family, but they did have high similarity with order members thought to be predators (Davidov, Huchon, Koval, & Jurkevitch, 2006).…”

Origin of eukaryotes as a symbiosis of parasitic α-proteobacteria in the periplasm of two-membrane-bounded sexual prekaryotes

“…15 Bdellovibrio-like α-proteobacterial predators have been recently discovered, and it has been suggested that this might have implications for the origin of mitochondria. 99 In our view selfish α-proteobacterial parasites had the ability to disrupt pre-karyotes' membranes. 15 Under this selective pressure the pre-karyote evolved various mechanisms to resist the aggressive infection of α-proteobacterial parasite.…”