Several research questions arising in the context of soil, rhizosphere and phyllosphere microbiology are addressed by focusing on a specific functional guild within the microbial communities: the methylotrophic microorganisms. These are characterized by their ability to use one-carbon compounds such as methanol or methane as source of carbon and energy. Methylotrophic microorganisms occur quite widespread in nature; they are common in soils, aquatic ecosystems, air, sediments and dust. Noteworthy is their consistent occurrence in association with plants. In particular diverse strains of the methylotrophic genus Methylobacterium are found in the phyllosphere of essentially all land plants. The key characteristics of this alphaproteobacterial genus are a facultative methylotrophic lifestyle and pink pigmentation (Figure 4). It appears likely that the successful plant colonization of Methylobacteriumstrains is linked to the utilization of plant-released methanol. Due to the consistent colonization of plants by this bacterial genus, it serves as a good model to study plant colonization strategies by microorganisms and adaptations to life in the phyllosphere.

A specific subgroup of methylotrophic bacteria are methanotrophic bacteria, which are defined by their ability to use methane as carbon and energy source. Methanotrophic bacteria represent the only biological sink for the greenhouse gas methane and are important players in the global methane cycle. They are frequently found at oxic/anoxic interfaces, e. g. in the rhizosphere of rice plants growing under flooded conditions, where they consume substantial amounts of the methane that is produced in the anoxic rice paddy. Moreover, methanotrophic bacteria are found in upland soils, where they oxidize atmospheric methane. Besides the well-known genera of methanotrophic bacteria, uncultivated representatives appear to play an important role in different soil ecosystems and the rice rhizosphere (Figure 5). Obtaining more information about the distribution and physiology of cultivated and uncultivated methanotrophs in soil and rhizosphere ecosystems is our research goal.