Lanthanide-dependent methanol metabolism in Sinorhizobium meliloti

Date of Award

8-2024

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Silvia Rossbach, Ph.D.

Second Advisor

Karim Essani, Ph.D.

Third Advisor

Benjamin Koestler, Ph.D.

Keywords

Lanthanides, methanol dehydrogenase, methylotrophy, Sinorhizobium meliloti

Access Setting

Masters Thesis-Abstract Only

Restricted to Campus until

8-1-2026

Abstract

Lanthanides, also known as rare earth elements, were thought to be biologically inert. However, the recent discovery of XoxF, a lanthanide-dependent methanol dehydrogenase, shed new light on the roles of lanthanides in biology. Lanthanide-dependent methanol metabolism was even found in bacterial genera that previously have not been described as methylotrophs, including Sinorhizobium. A homolog of the xoxF gene was found to be present in Sinorhizobium meliloti. S. meliloti is a soil bacterium that undergoes a symbiotic relationship with alfalfa plants by fixing atmospheric nitrogen within root nodules. While many studies on lanthanide-dependent methylotrophy have been performed mainly in the model organism Methylorubrum extorquens, little has been published about this pathway in S. meliloti. The presence of a single copy of the methanol dehydrogenase gene in the genome of S. meliloti makes it an excellent model to understand lanthanide-dependent methanol metabolism. In this study, a complementation experiment showed that XoxF, encoded by smb20173, is the sole lanthanide-dependent methanol dehydrogenase present in S. meliloti. The methanol dehydrogenase enzyme activity of XoxF was also demonstrated through an enzyme assay. Whole transcriptome analysis performed in this study confirmed a putative methanol metabolic pathway previously proposed for S. meliloti. Genes postulated to be involved in methanol metabolism were found to be highly upregulated when S. meliloti was grown with methanol and lanthanides, including a cluster of genes encoding an ABC transport system that is located downstream of the xoxF gene and putatively involved in the transport of lanthanides. This study expands our knowledge about the metabolic role of lanthanides in microorganisms.

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