Identification of the bacterial endosymbionts in leaf nodules of Pavetta (Rubiaceae)

Abstract

Three genera in the Rubiaceae (Pavetta, Psychotria and Sericanthe) harbour bacterial endosymbionts within leaf nodules or galls. The present paper identifies the bacterial endophytes in three leaf-nodulating Pavetta species. In order to reveal their identity and assess their phylogenetic position, 16S rRNA, recA and gyrB genes were sequenced from an extensive sampling of Burkholderia strains. This multigene approach results in a robust phylogeny, which places the bacterial endosymbionts of Pavetta at two distinct positions within the genus Burkholderia (class Betaproteobacteria), suggesting that leaf-nodulating endosymbionts within Pavetta have different origins. The endophytes of nodulated Psychotria species were recognized as the closest relatives to the Pavetta endosymbionts. Our results suggest that the endosymbionts of Pavetta represent novel species, which can be classified as 'Candidatus Burkholderia hispidae', 'Candidatus Burkholderia rigidae' and 'Candidatus Burkholderia schumannianae'.