Metabolic Interactions at the Mycobiont-Photobiont Interface in Lichens

Abstract

Lichen-forming fungi are, like plant pathogens or mycorrhizal fungi, a polyphyletic, taxonomically heterogeneous group of nutritional specialists (Table 1; Gargas et al. 1995). As ecologically obligate biotrophs, they acquire fixed carbon from a population of minute, extracellularly located algal and/or cyanobacterial cells. In contrast to pathogenic interactions of fungi and fungus-like organisms with unicellular algae (e.g., van Donk and Bruning 1992), the photobiont cells of lichen thalli are not severely damaged by the fungal partner. Geosiphon pyriforme, the only known fungal (zygomycetous) symbiosis with an intracellularly located cyanobacterium (Nostoc sp.; Mollenhauer 1992), is not normally considered as a lichen.