Burkholderia silvatlantica sp. nov., a diazotrophic bacterium associated with sugar cane and maize.

In a previous study, nitrogen-fixing isolates were recovered from the rhizosphere of maize and from surface-sterilized leaves of sugar cane cultivated in Rio de Janeiro, Brazil. On the basis of 16S rRNA gene sequence similarities, these isolates were identified as belonging to the genus Burkholderia, and whole-cell-protein profiles demonstrated that they are closely related to each other. In the present study, novel isolates were recovered from the roots of different sugar-cane varieties cultivated in diverse geographical regions of Brazil. Twenty-one nitrogen-fixing isolates were analysed using polyphasic taxonomy criteria, including DNA-DNA relatedness, 16S rRNA gene sequence similarities, fatty acid profiles, whole-cell-protein patterns and multilocus enzyme electrophoresis profiles, as well as morphological, physiological and biochemical characterization. The analysis confirmed that these isolates belong to a novel species within the genus Burkholderia, for which the name Burkholderia silvatlantica sp. nov. is proposed. The type strain, SRMrh-20(T) (=LMG 23149(T)=ATCC BAA-1244(T)), was isolated from the rhizosphere of maize var. Avantis A2345 cultivated in Seropédica, Rio de Janeiro.

Diazotrophic burkholderia species associated with field-grown maize and sugarcane.

Until recently, diazotrophy was known in only one of the 30 formally described species of Burkholderia. Novel N(2)-fixing plant-associated Burkholderia species such as B. unamae, B. tropica, and B. xenovorans have been described, but their environmental distribution is scarcely known. In the present study, the occurrence of N(2)-fixing Burkholderia species associated with different varieties of sugarcane and maize growing in regions of Mexico and Brazil was analyzed. Only 111 out of more than 900 isolates recovered had N(2)-fixing ability as demonstrated by the acetylene reduction assay. All 111 isolates also yielded a PCR product with primers targeting the nifH gene, which encodes a key enzyme in the process of nitrogen fixation. These 111 isolates were confirmed as belonging to the genus Burkholderia by using a new 16S rRNA-specific primer pair for diazotrophic species (except B. vietnamiensis) and closely related nondiazotrophic Burkholderia. In Mexico, many isolates of B. unamae (predominantly associated with sugarcane) and B. tropica (more often associated with maize) were recovered. However, in Brazil B. tropica was not identified among the isolates analyzed, and only a few B. unamae isolates were recovered from one sugarcane variety. Most Brazilian diazotrophic Burkholderia isolates (associated with both sugarcane and maize plants) belonged to a novel species, as revealed by amplified 16S rRNA gene restriction profiles, 16S rRNA gene sequencing, and protein electrophoresis. In addition, transmissibility factors such as the cblA and esmR genes, identified among clinical and environmental isolates of opportunistic pathogens of B. cenocepacia and other species of the B. cepacia complex, were not detected in any of the plant-associated diazotrophic Burkholderia isolates analyzed.