Fungal autolysis is the natural process of self-digestion of aged hyphal cultures, occurring as a result of hydrolase activity, causing vacuolation and disruption of organelle and cell wall structure. Previously, authors have considered individual aspects of fungal lysis, in terms of either an enzyme, a process or an organism. This review considers both the physiology and morphology of fungal autolysis, with an emphasis on correlations between enzymological profiles and the morphological changes occurring during culture degeneration. The involvement of the main groups of autolytic hydrolases is examined (i.e., proteases, glucanases, and chitinases), in addition to the effects of autolysis on the morphology and products of industrial bioprocesses. We call for a concerted approach to the study of autolysis, as this will be fundamental for research to progress in this field. Increased understanding will allow for greater control of the prevention, or induction of fungal autolysis. Such advances will be applicable in the development of antifungal medicines and enable increased productivity and yields in industrial bioprocesses. Using paradigms in existing model systems, including mammalian cell death and aging in yeast, areas for future study are suggested in order to advance the study of fungal cell death.

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Morphology and ␣-amylase production during submerged cultivation were examined in a wild-type strain (A1560) and in strains of Aspergillus oryzae in which chitin synthase B (chsB) and chitin synthesis myosin A (csmA) have been disrupted (ChsB/G and CM101). In a flowthrough cell, the growth of submerged hyphal elements was studied online, making it possible to examine the growth kinetics of the three strains. The average tip extension rates of the CM101 and ChsB/G strains were 25 and 88% lower, respectively, than that of the wild type. The branching intensity in the CM101 strain was 25% lower than that in the wild type, whereas that in the ChsB/G strain was 188% higher. During batch cultivation, inseparable clumps were formed in the wild-type strain, while no or fewer large inseparable clumps existed in the cultivations of the ChsB/G and CM101 strains. The ␣-amylase productivity was not significantly different in the three strains. A strain in which the transcription of chsB could be controlled by the nitrogen source-regulated promoter niiA (NiiA1) was examined during chemostat cultivation, and it was found that the branching intensity could be regulated by regulating the promoter, signifying an important role for chsB in branching. However, the pattern of branching responded very slowly to the change in transcription, and increased branching did not affect ␣-amylase productivity. ␣-Amylase residing in the cell wall was stained by immunofluorescence, and the relationship between tip number and enzyme secretion is discussed.Filamentous fungi, such as Aspergillus oryzae, are widely used for industrial enzyme production, since they are able to secrete large amounts of proteins (e.g., amylases, proteases, phytases, and lipases) into the medium. Filamentous fungi grow by hyphal extension and branching through processes that are regulated in a way that is still not completely understood. During submerged cultivation, the growing hyphal elements tend to entangle, and this affects the rheology of the cultivation medium and the mixing characteristics in an undesirable fashion. This results in poor mixing and poor mass transfer of the substrate, and it makes the morphologies of filamentous fungi an obvious, yet unanswered, challenge in process optimization. Recently, however, there have been major advances in the tools available for metabolic engineering of aspergilli (reviewed by McIntyre et al. [17]), such as developments in genomics, the increased number of suitable transformation vectors, and powerful image analysis tools that enable rapid quantification of the fungal morphology. This has made metabolic engineering of the morphology for process optimization possible.Metabolic engineering of morphology requires detailed knowledge of the relationships among productivity, growth, and morphology. The morphologies of filamentous organisms can be classified into macroscopic and microscopic morphologies (21), and techniques for analyzing morphology on both of these levels have advanced rapidly during the last decade (reviewed...

The dimorphic organism Mucor circinelloides is currently being investigated as a potential host for heterologous protein production. The production of ethanol on pentose and hexose sugars was studied in submerged batch cultivations to further the general knowledge of Mucor physiology, with a view to the minimisation or elimination of the by-product ethanol for future process design. Large amounts of ethanol were produced during aerobic growth on glucose under non-oxygen limiting conditions, which is indicative of M. circinelloides being a Crabtree-positive organism. Ethanol production on galactose or xylose was less significant. The response of the organism to increased ethanol concentrations, both as the sole carbon source and in the presence of a sugar, was investigated in terms of biomass formation and morphology.