Dr. Silvia Rossbach
Atmospheric nitrogen is in a form that is unavailable to plants. Nevertheless, there are nitrogen fixing bacteria that can be found either free-living or in association with plants. Sinorhizobium meliloti is a symbiotic nitrogen-fixing bacterium that infects legume plants such as alfalfa and induces specialized organs known as root nodules. In the nodule, the bacteria will fix the atmospheric nitrogen for use by the host plant, and in return, the plants supply the bacteria with carbon sources. Specialized carbon sources such as inositols may play a role in determining bacterial composition of the rhizosphere. The focus of this study is to characterize essential genes that are involved in inositol transport and catabolism in S. meliloti. The S. meliloti ibpA gene was found to be the first gene in an operon that encodes a periplasmic binding protein of an ABC transporter responsible for the transport of inositol isomers. A mutant with an insertion in the ibpA gene was tested for the ability to use inositol as sole carbon source. The ibpA mutant shows a delayed growth, but it regained growth after three days. It was concluded that the ibpA-iatA-iatP operon encodes a major inositol transporter, but that there may be also a second, minor inositol transporter present in S. meliloti. A candidate gene was identified based on homology, and mutants with insertions in this gene were constructed and their phenotypes were analyzed. The inositol (iol) genes are required for bacterial growth with inositol and S. meliloti mutant strains with Tn5 insertion in each of the individual iol genes were previously characterized with growth studies testing myo-inositol as the sole carbon source. Interestingly, the iolI gene involved in the catabolism of another isomer of inositol, D-chiro-inositol, still remains unidentified in S. meliloti. A candidate gene was discovered based on homology with the iolI gene of Bacillus subtilis and a mutant with an inserted antibiotic resistance cassette was constructed and its phenotype was analyzed. Plant inoculation studies will show whether inositol transport genes and D-chiro-inositol catabolism genes of S. meliloti are involved in establishing and maintaining an efficient nitrogen fixing symbiosis between rhizobia and legume plants.
WMU ScholarWorks Citation
Choong, Ee Leng; Thwaites, Mary; and Rossbach, Silvia, "Inositol Transport and Catabolism in Sinorhizobium meliloti" (2014). Research and Creative Activities Poster Day. 90.
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