A DIAZOTROPHIC BACTERIAL ENDOPHYTE ISOLATED FROM STEMS OF ZEA-MAYS L AND ZEA-LUXURIANS ILTIS AND DOEBLEY

The apoplastic fluids of field-grown Zea mays and Zea luxurians plants were isolated from surface sterilized stem tissue by centrifugation a nd spread on agar plates containing a nitrogen-free, defined medium. T he predominant bacterium isolated from these plates was characterized further. The ability of this bacterium to fix nitrogen was confirmed b y its ability to grow on a semi-solid, nitrogen-free medium and reduce N-15(2) to (NH3)-N-15 and acetylene to ethylene. Portions of the nifH and 16S rRNA genes from this organism were amplified by PCR and seque nced. The nifH gene, which codes for dinitrogenase reductase, from thi s organism is closely related to nifH from Klebsiella pneumoniae. Simi larly, the 16S rRNA gene sequences and carbon utilization tests groupe d it closely with K. pneumoniae. Based an these data, the isolates fro m Z. mays and Z. luxurians are tentatively classified as Klebsiella sp p. (Zea). The ability of this bacterium to contribute to the nitrogen economy of the corn plant is unknown.