Methane is an attractive low-priced feedstock used for the biotechnological production of value-added products. We developed a metabolically engineered strain of a type II methanotroph, Methylosinus trichosporium OB3b, capable of producing cadaverine and lysine from methane. The genome-scale metabolic model (GEM) of M. trichosporium OB3b, iMsOB3b_cadaverine, was used to predict metabolic fluxes leading to cadaverine and lysine and employed to find metabolic engineering targets for enhanced production of cadaverine and lysine. First, L-lysine decarboxylase, which converts L-lysine directly to cadaverine, was introduced into M. trichosporium OB3b using plasmid-based expression of two E. coli genes, cadA and ldcC. Next, several metabolic engineering strategies were employed to develop strains for improved lysine and cadaverine production from methane. The L-lysine biosynthetic pool was increased by overexpressing the lysC gene encoding aspartokinase II and the lysA gene encoding meso-diaminopimelate decarboxylase, and the pyc gene derived from Methylomonas sp. DH-1 was co-expressed. The engineered OB3b/cad3 strain produced a 10.4-fold higher titer of cadaverine (corresponding to 30.99 mg L⁻¹) than the initial strains. To improve cadaverine secretion, cadaverine–lysine antiporter cadB from E. coli was introduced into the OB3b/cad3 strain. The resulting strain, OB3b/cad4, produced 283.63 mg L⁻¹ of cadaverine with a volumetric productivity of 6.52 mg per g DCW per d using a gas bioreactor system. To our knowledge, this is the first demonstration for the production of amino acids for feed and diamine compound for polyamides from methane using engineered type II methanotrophic strains.

Propane is the major component of liquefied petroleum gas (LPG). Nowadays, the use of LPG is decreasing, and thus utilization of propane as a chemical feedstock is in need of development. An efficient biological conversion of propane to acetone using a methanotrophic whole cell as the biocatalyst was proposed and investigated. A bio-oxidation pathway of propane to acetone in Methylomonas sp. DH-1 was analyzed by gene expression profiling via RNA sequencing. Propane was oxidized to 2-propanol by particulate methane monooxygenase and subsequently to acetone by methanol dehydrogenases. Methylomonas sp. DH-1 was deficient in acetone-converting enzymes and thus accumulated acetone in the absence of any enzyme inhibition. The maximum accumulation, average productivity and specific productivity of acetone were 16.62 mM, 0.678 mM/h and 0.141 mmol/g cell/h, respectively, under the optimized conditions. Our study demonstrates a novel method for the bioconversion of propane to acetone using methanotrophs under mild reaction condition.