The marine gram-negative non-photosynthetic bacterium,
Agrobacterium ferrugineum IAM 12616
T forms one cluster with the species of the photosynthetic genus
Rhodobacter in phylogenetic trees based on molecules of 16S rRNA, 23S rRNA and DNA gyrases.
Agrobacterium ferrugineum and
Rhodobacter species are similar in that growth occurs without NaCl in the culture medium (optimal NaCl concentration for growth of
P. ferrugineus is 1%) and their major hydroxy fatty acid compositions are 3-hydroxy decanoic acids (3-OH 10:0) and 3-hydroxy tetradecanoic acids (3-OH 14:1). However,
A. ferrugineum differs from
Rhodobacter species in G+C content (58 mol% in
A. ferrugineum versus 64–73 mol% in
Rhodobacter species), in having an insertion in its 16S rRNA gene sequence, and in lacking photosynthetic abilities, bacteriochlorophyll
a and intracytoplasmic membrane systems. Furthermore, experiments using PCR and Southern hybridization show that
A. ferrugineum does not have
puhA gene and
puf genes localized near the opposite ends of the photosynthesis gene cluster of
Rhodobacter capsulatus. It suggests that
A. ferrugineum may not have any genes for photosynthesis. We propose the transfer of
A. ferrugineum IAM 12616
T to the genus
Pseudorhodobacter gen. nov. as
Pseudorhodobacter ferrugineus comb. nov. Although
Pseudorhodobacter ferrugineus disturbs the phylogenetic monophyly of the genus
Rhodobacter, this taxonomic proposal seems adequate until it has been clarified whether
P. ferrugineus possesses an incomplete photosynthetic apparatus.
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