CHARACTERIZATION OF GENES INVOLVED IN LANTHANIDE-DEPENDENT METHANOL GROWTH

Recent discoveries have demonstrated that some methylotrophic bacteria are able to utilize lanthanides, also known as rare earth elements, when growing on single carbon compounds such as methanol. Lanthanides are commonly found in electronic devices such as computer hard drives and smart phone batteries but sustainable acquisition of lanthanides does not yet exist. Methylobacterium extorquens AM1 is a model methylotrophic bacterium garnering attention due to its potential use in bioremediation of lanthanide contaminated sites and biorecycling of lanthanides from discarded electronics. While M. extorquens AM1 has been studied for over 50 years, the discovery of lanthanide containing enzymes is only five years old so very little is known about the requirements for operation of these enzymes. During the first step of methanol metabolism, methanol is oxidized to formaldehyde in the periplasmic space by methanol dehydrogenase (MeDH). Until recently, it was thought that the only MeDH in M. extorquens was calcium dependent and encoded by the mxaFI genes. However, we have now shown that the XoxF and ExaF enzymes directly use lanthanides in the catalysis of methanol to formaldehyde or formate and that expression of these genes is dependent on lanthanide presence. To identify genes required for lanthanide-dependent methanol growth, over 400 transposon mutants were isolated from three transposon mutant hunts and their insertion locations identified. Each mutant hunt identified different candidates with some overlap. We have created null mutations in over 40 candidate genes and have used phenotypic and biochemical analyses to characterize the role of these particular genes in lanthanide acquisition and transport, MeDH activity and expression. This work will further our understanding of how lanthanides function in biology provide us with information to best genetically engineer M. extorquens for recovery of lanthanides from recycled electronics, mining ores and contaminated soils.