Rubidibacter lacunae gen. nov., sp. nov., a unicellular, phycoerythrin-containing cyanobacterium isolated from seawater of Chuuk lagoon, Micronesia.

A unicellular cyanobacterium, designated KORDI 51-2(T), was isolated from surface seawater of Chuuk lagoon, Micronesia. The cells were wine-coloured rods and emitted red fluorescence under green excitation of an epifluorescence microscope. Thus, morphologically, the strain resembled Synechococcus species. However, based on 16S rRNA gene sequence similarities between strain KORDI 51-2(T) and related strains belonging to cyanobacteria, the novel strain was distantly related to members of the 'Halothece' cluster. However, sequence similarities between strain KORDI 51-2(T) and members of the 'Halothece' cluster were very low, ranging from 90.7 to 92.1 %, and phylogenetic analyses showed that the strain formed a distinct branch. Therefore, a polyphasic characterization including morphology, physiology and pigment composition was conducted to elucidate the taxonomic position of strain KORDI 51-2(T). The strain grew within a temperature range of 25-35 degrees C and a salinity range of 2-7 %. The optimal temperature and salinity were about 30 degrees C and 5 %, respectively. Strain KORDI 51-2(T) contained phycoerythrin, and the dominant carotenoid pigments were zeaxanthin, beta-carotene and echinenone. The DNA G+C content was 60.5 mol%. Based on phylogenetic analysis of the 16S rRNA gene sequence, and the physiological data and pigment compositions, strain KORDI 51-2(T) is considered to represent a new genus and novel species of cyanobacteria for which the name Rubidibacter lacunae gen. nov., sp. nov. is proposed. The type strain is KORDI 51-2(T) (=KCTC 40015(T)=UTEX L2944(T)).