Revisiting methylotrophy : the impact of lanthanides and lanthanide-dependent enzymes on the methylotrophic metabolic network

"The recent discovery of lanthanide (Ln3+)-dependent enzymes renewed interest in methylotrophs, although the impact of these enzymes is not understood. In Methylobacterium extorquens AM1, the Ca2+ -dependent MxaFI canonically oxidizes methanol to formaldehyde. The tetrahydromethanopterin (H4MPT) pathway oxidizes formaldehyde to formate. Formate is oxidized to CO2 by formate dehydrogenases (FDH) or partially reduced and assimilated. The genome of M. extorquens AM1 codes for three known Ln3+ -dependent genes: xoxF, xoxF2, and exaF. XoxF may oxidize both methanol and formaldehyde in some organisms while ExaF demonstrated efficient activity with formaldehyde in the presence of La3+ providing a potential alternative to the H4MPT pathway. RNAseq data provided by Dr. Nathan Good found downregulation of mxa genes and the first gene of the H4MPT pathway, fae, and upregulation of xoxF, xoxF2, and exaF in the presence of La3+ suggesting changes to carbon distribution. I found a sharp decrease in accumulation formaldehyde and fourfold increase in accumulation of formate in the presence of La3+ and hypothesized this was due to the activity of Ln3+ enzymes. I measured the minimum inhibitory concentration (MIC) to methanol metabolism and found decreased sensitivity of a 2206fae mutant from 10 mM to more than 125 mM in the presence of La3+. RNAseq suggested changes to the production of CO2 which I corroborated finding an increased CO2 production of 1.8-fold in the presence of La3+. Together, these data provide the first profile of Ln3+ -dependent methylotrophic metabolism and provides new avenues for research."--Page ii.