POLYPHASIC TAXONOMY IN THE GENUS BURKHOLDERIA LEADING TO AN EMENDED DESCRIPTION OF THE GENUS AND PROPOSITION OF BURKHOLDERIA-VIETNAMIENSIS SP-NOV FOR N-2-FIXING ISOLATES FROM RICE IN VIETNAM

The taxonomic position of nitrogen-fixing strains that were isolated f rom rhizosphere macerates of rice cultivated in the Binh Thanh region of Vietnam was determined by using polyphasic taxonomy. We determined the phylogenetic relationships of these organisms by performing DNA-rR NA hybridization experiments with a labeled rRNA probe from the type s train of Burkholderia cepacia, and we found that they belong to a sing le rRNA complex. Other members of this rRNA complex were also studied, and the N-2-fixing strains were found to be closely related to B. cep acia. In addition, all members of the rRNA complex containing B. cepac ia were studied by performing auxanographic and DNA-DNA hybridization experiments. Phenotypically and genotypically, the N-2-fixing isolates constitute a single cluster together with two strains of clinical ori gin. These organisms constitute a new Burkholderia species, for which the name Burkholderia vietnamiensis is proposed; the type strain of th is species is TVV75 (= LMG 10929). All members of this species can fix nitrogen. On the basis of our polyphasic taxonomy results and previou sly published data we concluded that the genus Burkholderia should be restricted to the following species: B. cepacia (the type species), Bu rkholderia mallei, Burkholderia pseudomallei, B. vietnamiensis, Burkho lderia gladioli, Burkholderia caryophylli, Burkholderia plantarii, Bur kholderia glumae, Burkholderia vandii, Burkholderia cocovenenans comb. nov., and Burkholderia andropogonis comb. nov. On the basis of genoty pic and phenotypic results [Alcaligenes] eutrophus, [Burkholderia] sol anacearum, and [Burkholderia] pickettii belong to two other clusters w hose internal structures must be studied further.