The expanding world of methylotrophic metabolism

Abstract

In the past few years, the field of methylotrophy has undergone a significant transformation in terms of discovery of novel types of methylotrophs, novel modes of methylotrophy, and novel metabolic pathways. This time has also been marked by the resolution of long-standing questions regarding methylotrophy and the challenge of long-standing dogmas. This chapter is not intended to provide a comprehensive review of metabolism of methylotrophic bacteria. Instead we focus on significant recent discoveries that are both refining and transforming the current understanding of methylotrophy as a metabolic phenomenon. We also review new directions in methylotroph ecology that improve our understanding of the role of methylotrophy in global biogeochemical processes, along with an outlook for the future challenges in the field.

Figure 1

The proposed roles of N-methylglutamate synthase (NMGS), γ-glutamylmethylamide synthase (GMAS), and N-methylglutamate dehydrogenase (NMGD) in the oxidation of methylamine and gene clusters encoding enzymes involved in this pathway.

Figure 2

Distinct roles of enzymes catalyzing H₄F-linked C1 transfer reactions. (a) FtfL, Fch, and MtdA are involved in assimilatory metabolism in Methylobacterium species during growth on methanol or methylamine. (b) MetF, FolD, and PurU are involved in dissimilatory metabolism of methylated compounds such as chloromethane.

Figure 3

The refined scheme of the glyoxylate regeneration cycle, now termed ethylmalonyl-CoA pathway (right), and its connection to the serine cycle (left). Gene names are shown in blue. Each of these genes has been mutated in Methylobacterium extorquens AM1 and the mutant phenotypes analyzed. The gene for succinyl-CoA hydrolase remains unknown.