Reclassification of Roseobacter gallaeciensis Ruiz-Ponte et al. 1998 as Phaeobacter gallaeciensis gen. nov., comb. nov., description of Phaeobacter inhibens sp. nov., reclassification of Ruegeria algicola (Lafay et al. 1995) Uchino et al. 1999 as Marinovum algicola gen. nov., comb. nov., and emended descriptions of the genera Roseobacter, Ruegeria and Leisingera

Abstract

A heterotrophic, antibiotic-producing bacterium, strain T5T, was isolated from the German Wadden Sea, located in the southern region of the North Sea. Sequence analysis of the 16S rRNA gene of this strain demonstrated close affiliation with Roseobacter gallaeciensis BS107T (99 % similarity), but the results of genotypic (DNA–DNA hybridization and DNA G+C content) and phenotypic characterization revealed that strain T5T represents a novel species. The novel organism is strictly aerobic, Gram-negative, rod-shaped, motile and forms brown-pigmented colonies. Strain T5T produces the antibiotic tropodithietic acid throughout the exponential phase which inhibits the growth of bacteria from different taxa, as well as marine algae. Strain T5T requires sodium ions and utilizes a wide range of substrates, including oligosaccharides, sugar alcohols, organic acids and amino acids. The DNA G+C content is 55.7 mol%. Comparative 16S rRNA gene sequence analysis revealed that strains T5T and Roseobacter gallaeciensis BS107T group with Leisingera methylohalidivorans as their closest described relative within the Roseobacter clade (97.9 and 97.6 % sequence similarity, respectively) and with Ruegeria algicola (96.6 and 96.5 % similarity, respectively) of the Alphaproteobacteria. Comparison of strains T5T and Roseobacter gallaeciensis BS107T with Roseobacter denitrificans and Roseobacter litoralis showed striking differences in 16S rRNA gene sequence similarities, chemical composition, pigmentation, presence of bacteriochlorophyll a and antibiotic production. On the basis of these results, it is proposed that Roseobacter gallaeciensis is reclassified as the type species of a new genus, Phaeobacter, as Phaeobacter gallaeciensis comb. nov. (type strain BS107T=CIP 105210T=ATCC 700781T=NBRC 16654T=DSM 17395T). Strain T5T (=LMG 22475T=DSM 16374T) is proposed as the type strain of a novel species of this genus, Phaeobacter inhibens sp. nov. At the same time, emended descriptions are provided of the genera Roseobacter, Ruegeria and Leisingera, as well as reclassifying Ruegeria algicola as the type species of a new genus, Marinovum, with the name Marinovum algicola comb. nov.