Development of an engineered methanotroph-based microbial platform for biocatalytic conversion of methane to phytohormone for sustainable agriculture

Methane is an important target for reducing greenhouse gases emission, owing to its abundance and highly global warming potential. Bioconversion of methane to value-added products, therefore, has become a promising and sustainable approach for industrial biomanufacturing. Herein, we metabolically engineered an obligate methanotroph Methylotuvimicrobium alcaliphilum 20Z to overproduce L-tryptophan and its derivative indole 3-acetic acid (IAA), a phytohormone, from methane. The engineered RS00 strain initially produced tryptophan from methane with a titer of 39.6 mg/L at 144 h of cultivation. The highest titer of IAA of 10.5 mg/L from methane was obtained in RS01 strain under P-tac promoter. Moreover, xylose, a carbon source derived from lignocellulosic biomass used as co-substrate, could enhance the titers of tryptophan and IAA in RS00 and RS01 strains by 60% and 82%, respectively. Remarkably, we proposed a proof-of-concept for the development of methanotroph-based plant growth-promoting bacteria (PGPB) which can utilize and convert methane into phytohormones to induce beneficial adaptation and growth promotion of plants. In this study, under saline-alkaline conditions, the germination percentage and elongation of the shoots and roots of wheat seeds treated with the IAA-producing strain were significantly improved, being 114%, 199% and 362% higher than those of control treatments, respectively. Our findings provide a novel methanotrophic platform for the conversion of renewable sources to value-added products. Additionally, the strategies and concepts presented here could be further expanded and applied to other methanotrophic hosts to develop biofertilizers that promote plant growth while mitigating methane and reducing chemical fertilizer use for sustainable agriculture production.