Ecology of the methylotrophic bacteria on living leaf surfaces

Pink‐pigmented, facultatively methylotrophic bacteria (PPFMs) are a substantial part of the aerobic, heterotrophic, microflora of young leaf surfaces. They were most numerous on white clover ( Trifolium repens ) leaves in the summer. The pink bacteria averaged 36% of the total heterotrophic count/cm 2 , with a range of 3 to 79%. The growth of PPFMs on multicarbon compounds is much lower than that of other numerically important leaf heterotrophs. Free methanol of endogenous origin, is present in growing leaves. The availability of methanol at the leaf surface may allow the PPFMs to compete successfully with other heterotrophs that require multicarbon compounds, that are also leached from the growing plant surfaces. SEM studies showed epiphytic bacteria to be most abundant near the margins of the abaxial surfaces of leaves. Microcolonies of bacteria on leaf surfaces were often covered with a thin layer of material, the source and nature of which has not been determined.