K-102. The Connection between Methylotrophy and Iron Homeostasis in Methylobacterium extorquens AM1

L. D. Palmer, E. Skovran, M. E. Lidstrom;
Univ. of Washington, Seattle, WA.

Methylotrophic bacteria are important in the global carbon cycle and offer potential for bioindustrial production of value-added products from methanol. Though methylotrophy in Methylobacterium extorquens has been studied for decades, connections between methylotrophy and other metabolic pathways remain unknown. Microarrays comparing chemostat cells grown with methanol to those grown with succinate showed an increase in gene expression of iron uptake genes during methanol growth, suggesting an increased iron requirement during methylotrophic growth. Here, we demonstrate this increased iron requirement by growth analysis using dipyridyl as an iron chelator. Cells grown with methanol were more sensitive to iron chelation than those grown with succinate. Cells grown with both carbon sources showed an intermediate sensitivity to iron chelation. Parallel studies with a strain containing a null mutation in qscR, the serine cycle regulator, suggest QscR may regulate both methylotrophic carbon assimilation and iron homeostasis. The qscR mutant strain is deficient in methanol growth, while microarrays in the qscR mutant strain show that QscR may to activate iron uptake genes. Gel retardation assays demonstrate a direct binding to the promoter regions of iron uptake genes. In addition, QscR is a known auto-repressor, and in in vitro studies, iron increases the ability of QscR to bind to its own operator, suggesting a mechanism for self-regulation and coordination of methylotrophic metabolism and iron levels. Future work will characterize the involvement of QscR in iron homeostasis in vivo, including promoter fusion experiments testing expression of iron uptake genes in the wild-type strain and the qscR mutant strain. This regulation scheme may allow fine-tuning of iron levels during methylotrophic growth and may offer a novel mechanism to regulate iron levels in the cell.