Isolation, pure culture and characterization of Serratia symbiotica sp. nov., the R-type of secondary endosymbiont of the black bean aphid Aphis fabae.

An intracellular symbiotic bacterium was isolated from the flora of a natural clone of the black bean aphid Aphis fabae. The strain was able to grow freely in aerobic conditions on a rich medium containing 1 % of each of the following substrates: glucose, yeast extract and casein peptone. Pure culture was achieved through the use of solid-phase culture on the same medium and the strain was designated CWBI-2.3(T). 16S rRNA gene sequence analysis revealed that strain CWBI-2.3(T) was a member of the class Gammaproteobacteria, having high sequence similarity (>99 %) with 'Candidatus Serratia symbiotica', the R-type of secondary endosymbiont that is found in several aphid species. As strain CWBI-2.3(T) ( = LMG 25624(T) = DSM 23270(T)) was the first R-type symbiont to be isolated and characterized, it was designated as the type strain of Serratia symbiotica sp. nov.