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CHAPTER 1: INTRODUCTION - THE FUNGI AND FUNGAL ACTIVITIES

This chapter covers the following major topics:

The place of fungi in the "Tree of Life" - setting the scene
The characteristic features of fungi: defining the fungal kingdom
The major activities of fungi as parasites, symbionts and saprotrophs
Fungal biotechnology

SAMPLE TEXT:

Fungi are a unique group of organisms, different from all others in their behaviour and cellular organisation. Fungi also have an enormous range of activities - as pathogens of crop plants or humans, as decomposer organisms, as experimental ‘model organisms’ for investigating genetics and cell biology, and as producers of many important metabolites. The uniqueness of fungi is a prominent feature of this book, which adopts a functional approach, focusing on topics of inherent interest and broad significance in fungal biology. The uniqueness of fungi is reflected in the fact that have the status of a Kingdom, equivalent to the plant and animal Kingdoms. So, fungi represent one of the three major evolutionary branches of multicellular organisms.

In terms of biodiversity, there are estimated to be at least 1.5 million different species of fungi, but only about 75,000 species (about 5% of the total) have been described to date. For comparison, there are estimated to be 4.9 million arthropod species and about 420,000 seed plants (Hawksworth, 2001, 2002). If the estimate of the number of fungal species is even remotely accurate then we still have much to learn, because even the fungi that we know about play many important roles. To set the scene, we can mention just a few examples.

• Fungi are the most important causes of crop diseases, responsible for billions of pounds worth of damage each year, and for periodic devastating disease epidemics.

• Fungi are the main decomposers and recyclers of organic matter, including the degradation of cellulose and wood by the specialised enzyme systems unique to fungi.Fungi produce some of the most toxic known metabolites, including the carcinogenic aflatoxins and other mycotoxins in human foods and animal feedstuffs.

• With the advance of AIDS and the increasing role of transplant surgery, fungi are becoming one of the most significant causes of death of immunocompromised and immunosuppressed patients. Fungal diseases that were once extremely rare are now commonplace in this sector of the population.

• Fungi have an enormous range of biochemical activities that are exploited commercially – notably the production of antibiotics (e.g. penicillins), steroids (for contraceptives), cyclosporins (used as immunosuppressants in transplant surgery), and enzymes for food processing and for the soft drinks industry.

• Fungi are major sources of food. They are used for bread-making, for mushroom production, for several traditional fermented foods, for production of Quorn™ mycoprotein – now widely available in supermarkets and the only survivor of the many “single-cell protein” ventures of the late 1900s. And, of course, for the production of alcoholic drinks.

• Fungi can be used as ‘cellular factories’ for producing heterologous (foreign) gene products. The first genetically engineered vaccine approved for human use was produced by engineering the gene for hepatitis B surface antigen into the yeast (Saccharomyces cerevisiae) genome. In this way the antigen can be produced and exported from the cells, then purified from the growth medium.

• The genome sequences of several fungi have now been determined, and in several cases the genes of fungi are found to be homologous (equivalent) to the genes of humans. So, fungi can be used to investigate many fundamental cell-biological processes, including the control of cell division and differentiation relevant to biomedical research.

• Fungi are increasingly being used as commercial biological control agents, providing alternatives to chemical pesticides for combating insect pests, nematodes and plant-pathogenic fungi.

The first part of this book deals with the growth, physiology, behaviour, genetics and molecular genetics of fungi, including the roles of fungi in biotechnology. This part also includes an overview of the main fungal groups (Chapter 2). The second part covers the many ecological activities of fungi – as decomposers of organic matter, as spoilage agents, as plant pathogens, plant symbionts, and as pathogens of humans. A final chapter is devoted to the ways of preventing and controlling fungal growth, because this presents a major challenge in modern Fungal Biology.

Images from Chapter 1. Click on the thumbnails for a larger image NOTE: some images (shown as WWW) link you directly to a remote website
Fig. 1.1 Fig. 1.4b Fig. 1.7b (see www)	Fig. 1.2 Fig. 1.5 Fig. 1.8a Fig. 1.9b	Fig. 1.3 (see www) Fig. 1.6 Fig.1.8b Fig. 1.10	Fig. 1.4a Fig. 1.7a (see www) Fig. 1.9a

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