In taxonomy

Alpha taxonomy

Alpha taxonomy is the discipline concerned with finding, describing and naming species of living or fossil organisms. This field is supported by institutions holding collections of these organisms, with relevant data, carefully curated: such institutes include natural history museums, herbaria and...

, Ruegeria is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of the Rhodobacteraceae

Rhodobacteraceae

The Rhodobacteraceae are a family of proteobacteria, given their own order within the alpha subgroup. Like all proteobaceria, they are gram-negative. It contains chemoorganotrophs and photoheterotrophs bacteria. Many occur in aquatic habitats....

. This genus was formerly known as the marine Agrobacterium

Agrobacterium

Agrobacterium is a genus of Gram-negative bacteria established by H. J. Conn that uses horizontal gene transfer to cause tumors in plants. Agrobacterium tumefaciens is the most commonly studied species in this genus...

before they were reclassified in 1998. It bears in fact the name of Wolfgang Rüger, a German microbiologist, for his contribution to the taxonomy of marine species of Agrobacterium.

Characteristics

The genus is characterised by members who are:

• Gram-negative
  Gram-negative
  Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
  
   — like all Proteobacteria
• ovoid to rod-shaped cells 0.6–1.6 × 1.0–4.0 µm
• Motile by polar flagella, or nonmotile
• non-sporeformers
• Aerobic
• Oxidase and catalase positive
• No photosynthetic growth
• Bacteriochlorophyll a is absent — feature absent to Sulfitobacter, Sagittula, Octadecabacter, Ruegeria and Antarctobacter, but present in Roseobacter and to a lesser extent Staleya, Roseivivax and Roseovarius
• Major quinone is ubiquinone 10 — common in most alphaproteobacteria and mitochondria, an organelle descending from the Rickettsiales (alphaproteobacteria)
• The mol% G � C of the DNA is 55–59
• the type species is R. altantica — unrelated to Pseudoalteromonas altantica, a gammaproteobacterium
• member of the family Rhodobacteraceae, which is phenotypically, metabolically, ecologically diverse and defined based on 16S sequences data.

Phylogenetically it is very close to the genus Silicibacter, but the two remain separate species due to phenotypic differences — two species fo which this is problematic are Ruegeria lacuscaerulensis and Ruegeria pomeroyi.

Two species that have been removed from the genus are Marinovum algicola (Ruegeria algicola) and Thalassobius gelatinovorus (Ruegeria gelatinovora).^{[and refs therein]}

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