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Soluble chitinase activity was purified from yeast and hyphal cells of Candida albicans following ammonium sulphate fractionation, gel-filtration and anion-exchange chromatography. Activity from both cell types resolved into three peaks with identical Mr of 79, 58 and 33 kDa. In both yeast and hyphae the 33 kDa chitinase was the predominant activity. Differences were observed in the relative distribution of the three chitinases in yeast and hyphae and in their substrate specificities. The 33 kDa protein showed preference for the longer chain length glycoside substrates suggesting (endo-) chitinase activity. In contrast, the 79 kDa protein exhibited activity against short and long chain glycosides, suggesting an agglomeration of chitinase and N-acetylglucosaminidase activities. Three separate activities were resolved by gel-filtration but after non-denaturing PAGE a number of bands exhibiting chitinase activity was detected indicating the presence of a complex chitinase system in Candida albicans.

Four ectomycorrhizal basidiomycetes ( Boletinus cavipes, Paxillus involutus, Suillus variegatus and Pisolithus tinctorius ), two pathogenic root-infecting basidiomycetes ( Heterobasidion annosum and Armillaria ostoyae ) and the oomycete Phytophthora cinnamomi were screened for chitinolytic activity in liquid culture. N -Acetylglucosaminidase, exo- and endo-chitinase activity were distinguished using fluorogenic 4-methylumbelliferyl substrates. N -Acetylglucosaminidase was the predominant enzyme activity recorded: exochitinase was the predominant chitinase. The pathogenic basidiomycetes had higher specific activities against all substrates than the ectomycorrhizal fungi. There was considerable variation in activity between the ectomycorrhizal isolates. P. cinnamomi showed N -acetylglucosaminidase activity only. In general, chitinolytic activities were highest when chitin was present in the growth medium and were repressed in the presence of glucose. Diammonium phosphate did not repress chitinolytic activities.

This account reflects diverse aspects of hyphal growth and development that I have encountered since first becoming interested in fungi. Apical growth is discussed, with particular reference to the phenomena of hyphal maturation and the formation of helical hyphae. It is contrasted with cases of intercalary growth and reversed growth of hyphae. Localization of chitin synthesis at the apex and at other particular sites in the wall is described in detail. It is suggested that chitin microfibrils are synthesized at hyphal tips and at other sites by a transmembrane enzyme complex of several polypeptides allosterically regulated by effector molecules but also perhaps by local physical stress of the membrane. Behaviour of hyphae is discussed with examples of mating zygophores, of contact sensing of surfaces and of responses to applied electric fields.

As undifferentiated mycelia of Botrytis cinerea aged, the leading hyphae extended faster and became wider, to form mature differentiated mycelia. There was a direct correlation between hyphal extension rate and the square of hyphal diameter. Equivalent hyphae of Mucor rouxii also extended faster and became wider as colonies aged, but did not show this direct correlation. The wider, faster growing leading hyphae of differentiated mycelia of both fungi were much more susceptible to bursting by treatment with nikkomycin than were hyphae in young colonies. Those of B. cinerea were also much more susceptible to bursting by echinocandin B. Regrowth of surviving hyphae after treatment with echinocandin B was characterized by multiple branching of both young and old hyphae. Echinocandin B had no effect on M. rouxii. Spore germination of B. cinerea was inhibited by nikkomycin, and germ-tubes became swollen. Spore germination of B. cinerea was inhibited by nikkomycin, and germ-tubes became swollen. Spore germination of M. rouxii was more sensitive than that of B. cinerea, with spores becoming swollen and producing multiple germ-tubes. Echinocandin B caused spores of B. cinerea to swell abnormally and produce multiple germ-tubes.

A number of fungi were grown on defined media containing uniformly labelled [14C]glucose with and without additional chitin, to examine how the presence of chitin affected growth and the distribution of 14C between cytoplasm and cell wall. Chitin significantly enhanced the growth of Heterobasidion annosum Boletinus cavipes and Paxillus inoolutus. These fungi, with the exception of H. annosum, also incorporated a lower proportion of assimilated 14C into their cell walls. The specific activity of 14C in the fungi screened was generally reduced in the presence of chitin indicating incorporation of C from chitin in fungal tissue. In the case of Phytophthora cinnamomi there was a significant increase in specific activity. These data indicate that patterns of carbon allocation in both chitinous and non-chitinous fungi change in the presence of chitin in the external medium.