Methylobacterium as a key symbiont in plant-microbe interactions: Its ecological and agricultural significance

Pink-pigmented facultative methylotrophs (PPFMs), encompassing the genera Methylobacterium and Methylorubrum, can utilize reduced one-carbon compounds such as methanol, methylamine, formaldehyde, and formate as carbon and energy sources. They are commonly associated with plants, particularly on leaf surfaces (phyllosphere), where their methylotrophic metabolism offers a significant adaptive advantage over other bacterial species. These genera hold quite diverse species with unique phenotypes. Many studies report plant growth-promoting activity of the genera due to their ability to produce plant hormones and help plants acquire nutrients. Also, the ecology of the genera that enables them to survive in such a harsh environment exposed to ultraviolet light, fluctuating temperature and humidity, and limited nutrients is the key to understanding their diversity, functions, and adaptations supported by their genotypes. In this review, we summarize their taxonomy diversified by their genotypes and niches, functions involved in plant growth promotion and survival in the phyllosphere, and practical application of the bacteria for agricultural purposes.