Burkholderia tropica sp. nov., a novel nitrogen-fixing, plant-associated bacterium In an ecological survey of nitrogen-fixing bacteria isolated from the rhizosphere and as endophytes of sugarcane, maize and teosinte plants in Brazil, Mexico and South Africa, a new phylogenetically homogeneous group of N 2 -fixing bacteria was identified within the genus Burkholderia. This polyphasic taxonomic study included microscopic and colony morphology, API 20NE tests and growth on different culture media at different pH and temperatures, as well as carbon source assimilation tests and whole-cell protein pattern analysis. Analysis of 16S rRNA gene sequences showed 99?2-99?9 % similarity within the novel species and 97?2 % similarity to the closest related species, Burkholderia sacchari. The novel species was composed of four distinct amplified 16S rDNA restriction analysis groups. The DNA-DNA reassociation values within the novel species were greater than 70 % and less than 42 % for the closest related species, B. sacchari. Based on these results and on many phenotypic characteristics, a novel N 2 -fixing species is proposed for the genus Burkholderia, Burkholderia tropica sp. nov., with the type strain Ppe8 T (=ATCC BAA-831

A polyphasic taxonomic study involving DNA-DNA hybridization, whole-cell protein electrophoresis, and 16S ribosomal DNA sequence analysis revealed that a group of Burkholderia cepacia-like organisms isolated from the rhizosphere or tissues of maize, wheat, and lupine belong to B. cepacia genomovar III, a genomic species associated with "cepacia syndrome" in cystic fibrosis patients. The present study also revealed considerable protein electrophoretic heterogeneity within this species and demonstrated that the B. cepacia complex consists of two independent phylogenetic lineages.In a survey of nonnative plant rhizosphere bacteria conducted in La Côte Saint André (France) with maize and in Kapunda (South Australia, Australia) with wheat, high levels of two groups of Burkholderia strains were found. The first group was characterized by using a polyphasic approach and formed a new taxon, Burkholderia graminis (15). Strains of the second group (designated phenon B) were found to be closely related to the Burkholderia cepacia complex; large numbers of these strains were present on roots, and more recently, new isolates were also obtained from inside the tissues of wheat and lupine in Kapunda (Table 1). Here, characterization of this taxonomic group was revisited by including reference strains of the B. cepacia complex in DNA-DNA hybridization, whole-cell protein electrophoretic, and 16S ribosomal DNA (rDNA) sequence analyses.Total DNA-DNA hybridization analyses were performed by using two methods, one involving tritiated reference DNAs (Table 2) and one involving photobiotin-labeled probes (Table 3). In a preliminary study, the two methods showed good correlation. For instance, the levels of hybridization of strain AUS 27 DNA with DNA of strain LMG 12614 were 65% when tritiated DNA was used and 63% when photobiotin-labeled DNA was used.In the first experiments we used tritiated reference DNAs of eight isolates, including two rhizosphere isolates (AUS 27 and C3B1M), one recent cystic fibrosis isolate (1-36) T ), and three recent cystic fibrosis isolates (strains 751, 1-36, and 1-47) were hybridized with these radioactively labeled DNAs. When hybridized with labeled DNA of strain AUS 27, all rhizosphere isolates except m35b showed levels of DNA-DNA hybridization greater than 65% and differences in melting temperatures (⌬T m values) less than 5°C, indicating that they belong to the same genomic species (12). When they were hybridized with labeled DNA of strain C3B1M, slightly lower values (as low as 61%) were obtained, indicating a certain degree of genomic heterogeneity in this species. Strain m35b showed significant but low levels of hybridization (40 to 48%) with all reference strains and thus does not belong to any of the genomovars examined. The possibility that this strain could belong to Burkholderia stabilis was not eliminated and will be tested further. B. cepacia genomovar III reference strains exhibited levels of hybridization of 58 to 76% with labeled DNA of strain AUS 27, indicating that the rhizosphere isola...