Honors Students' Abstracts
Identifying and Characterizing the Microbial Community of Dune Lupine
Lupinus chamissonis (dune lupine) is a nodulating species of the legume family present in the Ballona wetlands and El Segundo sand dunes near Loyola Marymount University. Legumes such as dune lupine have symbiotic relationships with nitrogen-fixing soil bacteria (Rhizobia) that reside in special root structures called nodules. We are interested in characterizing the bacteria that reside in these nodules as it is the first step towards screening for plant growth promoting bacteria (PGPR) that could be useful in restoration efforts. Nodules were isolated from roots of dune lupine, surface sterilized, crushed, and plated on selective media. To identify the bacterial isolates, the polymerase chain reaction (PCR) was performed on the 16S ribosomal DNA and the products were sequenced and compared to the BLAST database. Five bacteria were identified as Bradyrhizobium japonicum, Rhizobium lusitanum, Variovorax paradoxus, Methylobacterium tardum, and Mesorhizobium sp. Strains were screened for plant growth promoting properties such as cellulase activity, phosphate solubilization, and ACC deamination. R. lusitanum tested positive for both cellulase activity and phosphate solubilization, V. paradoxus tested positive for cellulase activity and ACC deamination, and Mesorhizobium sp. tested positive for cellulase activity and phosphate solubilization. Sterile plants were inoculated with both individual strains and in combination to determine which bacteria were able to induce nodulation in plants. From this, it was determined that only B. japonicum is able to induce nodulation independently while the other bacteria colonize nodules but do not nodulate when inoculated without B. japonicum. In addition, genes controlling nodulation and nitrogen fixation are currently being isolated using PCR.