Structure and function of fungal zoospores: ecological implications

Recent research suggests that fungal zoospores have important roles in ecosystems. Ultrastructural characteristics of zoospores and sequences of ribosomal RNA genes are increasingly being used in taxonomic and phylogenetic studies with zoosporic fungi. However, our current knowledge of the physiology and ecology of zoospores lags far behind our knowledge of phylogenetic relationships. Some aspects of the ecology of fungal zoospores are discussed in this review. Fungal zoospores have two mechanisms for active short range dispersal: flagellar and amoeboid movement. Flagellar movement is more common in open water and amoeboid movement more common on surfaces. All phases of the life cycle can be passively transported by currents in water for long range dispersal. As far as is known the zoospore never has a cell wall but can have a cell coat. This may cause zoospores to be more susceptible to damage by osmotic and mechanical forces than other phases in the life cycle. The environmental cues for release of zoospores are not understood. Zoospores can often respond to both light and chemical gradients. The behavior of zoospores may influence the structure of the colony formation. Little is known about the modes of nutrition of zoospores. Some zoospores may be osmotrophic but there is no evidence for holozoic nutrition.