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Hyphae are microscopic filaments that elongate and branch to create networks of interconnected tubes. Understanding how they work remains a formidable challenge in experimental mycology. Important advances in hyphal research in the 20th century came from electron microscopy, which revealed clusters of cytoplasmic vesicles in the cell apex, and biochemical studies that identified the cell wall materials that are assembled at the tip. Early genetic experiments on hyphae based on mutant analysis were disappointing and provided little information on the relationship between genotype and phenotype. Progress has come more recently, in the first decades of this century, by combining the techniques of molecular genetics with modern imaging methods. Live-cell imaging has allowed us to study the dynamics of cell components in strains of fungi engineered with plasmids encoding proteins fused to fluorescent probes. This technology has provided significant insights on the growth process and yet the fundamentals of hyphal growth remain elusive.

Cell size is an important variable in the study of cellular growth, metabolism, and the cell cycle. The large size of Amoeba proteus and the ease with which it can be collected and cultured have made it a star in biology education—and it was a model for research on cell biology before the introduction of molecular genetic methods. Measuring the cytoplasmic density of a single amoeba without modern instrumentation seems like a difficult task, but this was done with supreme accuracy in the 1940s. The solution was based on the familiar Cartesian diver that is used to demonstrate Archimedes’s principle. It required the fabrication of a tiny diver that would respond to the additional mass of a cell. Experiments using this method allowed investigators to study changes in size and density associated with feeding, starvation, and cell division. This research is an illustration of the ingenuity of cell biologists in the pre-molecular genetic era of their field, which is often overlooked by contemporary scientists. The consideration of the mass, density, and buoyancy of free-living amoebas encourages a new hypothesis about the evolution of testate amoebas.

A new study of truffle fungi in Patagonia reveals the importance of native bird species in spore dispersal. This has wide implications for the study of animal-fungal symbioses in the Southern Hemisphere.

Like other cells, fungal hyphae show exquisite sensitivity to their environment. This reactiveness is demonstrated at many levels, from changes in the form of the hypha resulting from alterations in patterns of exocytosis, to membrane excitation, and mechanisms of wound repair. Growing hyphae detect ridges on surfaces and respond to restrictions in their physical space. These are expressions of cellular consciousness. Fungal mycelia show decision-making and alter their developmental patterns in response to interactions with other organisms. Mycelia may even be capable of spatial recognition and learning coupled with a facility for short-term memory. Now is a fruitful time to recognize the study of fungal ethology as a distinctive discipline within mycology.

Este livro conta a história surpreendente da importância da levedura no desenvolvimento da civilização humana. “Era uma vez um micróbio que…” passou a fazer parte da produção de cerveja, de vinho e de pães, há cerca de dez mil anos. Desde então, nunca mais deixamos de ser parceiros desse fungo extraordinário. No século XIX tomamos consciência de sua existência e passamos a aplicar conhecimentos científicos para melhorar os processos de produção de alimentos. Com o tempo, esse fungo unicelular demonstrou ser um excelente material para estudos científicos, e muito do que sabemos hoje em biologia, incluindo a cura de inúmeras doenças, foi desvendado com a ajuda da levedura. Até as mudanças climáticas, problema fundamental, podem ser combatidas usando biocombustíveis produzidos por leveduras, que também vivem em nossa pele e em nosso sistema digestivo. Usando uma linguagem acessível e que provoca a curiosidade do leitor, mas sempre com embasamento científico, esta obra abre nossos olhos para a poderosa e indissociável realidade microscópica que nos envolve.

Despite the longstanding use of dried mushrooms and mushroom extracts in traditional Chinese medicine, there is no scientific evidence to support the effectiveness of these preparations in the treatment of human disease. Consumers should evaluate assertions made by companies about the miraculous properties of medicinal mushrooms very critically. The potential harm caused by these natural products is another important consideration. In a more positive vein, the presence of potent toxins and neurotropic compounds in basidiomycete fruit bodies suggests that secondary metabolites with useful pharmacological properties are widespread in these fungi. Major investment in controlled experiments and objective clinical trials is necessary to develop this natural pharmacopeia.

This study concerns the thermotolerance of spores of mesophilic fungi isolated from a tropical semi-arid habitat subject to dry season fire in the Western Ghats, southern India. Among 25 species of Ascomycota isolated from leaf litter, nine were able to grow after incubation in a drying oven for 2h at 100°C; the spores of two of these species survived 2h incubation at 110°C, and one survived exposure to 115°C for 2h. The range of thermotolerance among mesophilic fungi isolated from the leaf litter was surprising: filamentous fungi from other habitats, including species that colonize scorched vegetation after fires and thermophilic forms occurring in self-heating plant composts, cannot survive even brief exposure to such high temperatures. It is possible that the exceptional heat resistance of the Indian fungi is related to adaptations to surviving fires. Genetic analysis of the physiological mechanisms of heat resistance in these fungi offers prospects for future biotechnological innovations. The discovery of extreme thermotolerance among common saprotrophs shows that this physiological trait may be more widespread than recognized previously, adding to concern about the evolution of opportunistic pathogens on a warmer planet. The fungi in this study are among the most heat-resistant eukaryotes on record and are referred to here as 'Agni's Fungi', after the Hindu God of Fire.

Active discharge of basidiospores in most species of Basidiomycota is powered by the rapid movement of a droplet of fluid, called Buller’s drop, over the spore surface. This paper is concerned with the operation of the launch mechanism in species with the largest and smallest ballistospores. Aleurodiscus gigasporus (Russulales) produces the largest basidiospores on record. The maximum dimensions of the spores, 34 × 28 µm, correspond to a volume of 14 pL and to an estimated mass of 17 ng. The smallest recorded basidiospores are produced by Hyphodontia latitans (Hymenochaetales). Minimum spore dimensions in this species, 3.5 × 0.5 µm, correspond to a volume of 0.5 fL and mass of 0.6 pg. Neither species has been studied using high-speed video microscopy, but this technique was used to examine ballistospore discharge in species with spores of similar sizes (slightly smaller than A. gigasporus and slightly larger than those of H. latitans). Extrapolation of velocity measurements from these fungi provided estimates of discharge distances ranging from a maximum of almost 2 mm in A. gigasporus to a minimum of 4 µm in H. latitans. These are, respectively, the longest and shortest predicted discharge distances for ballistospores. Limitations to the distances traveled by basidiospores are discussed in relation to the mechanics of the discharge process and the types of fruit-bodies from which the spores are released.

Rhizomorphs of wood-decay basidiomycetes are root-like structures produced by the coordinated growth of thousands of hyphae. Very little is known about their development nor the way that they penetrate soils and rotting wood. In this study, we applied techniques used in previous studies on hyphae to explore the mechanics of the invasive growth process in Armillaria gallica. Growth rate measurements were made in media with different gel strengths. The osmolyte composition of rhizomorph sap was determined spectroscopically and the forces exerted by growing tips were measured using a force transducer. Cultured rhizomorphs extended at much faster rates than unbundled hyphae (3.5 mm d−1 versus 1.5 mm d−1) and their growth accelerated in response to increased medium gel strength (to 7.4 mm d−1). Measurements of rhizomorph osmolality provided a turgor pressure estimate of 760 kPa (7.5 atm.), and spectroscopic analysis showed that this pressure was generated by the accumulation of erythritol, mannitol, and KCl. Forces exerted by growing tips ranged from 1 to 6 mN, corresponding to pressures of 40–300 kPa (0.4–3.0 atm.). Pressures exerted by extending rhizomorphs are comparable to those produced by individual vegetative hyphae. This suggests that the mechanical behavior of hyphae is similar whether they grow as unbundled cells or aggregate to form macroscopic rhizomorphs.

This article reviews recent progress in understanding the mechanics of hyphal growth. The pressurization of hyphae by osmosis is often considered an important feature of the tip growth process. But although the hydrostatic pressure within the cytoplasm smooths the expanding surface of these cells, there is little evidence that high levels of turgor are necessary for growth until the hypha encounters friction from its surroundings. Research on movement and growth processes in other kinds of cells, including amoebae and pollen tubes, has done a great deal to inform recent studies on hyphae. Experiments on pressure waves and rhythmic or pulsatile growth are particularly significant and are discussed in relation to the erratic extension rate of hyphae. Significant findings have also come from research on the hyphal cytoskeleton and on the biomechanics of invasive growth. It has been clear for some time that turgor powers the propulsion of hyphae through solid materials and experiments using new techniques have quantified the relevant forces.

‘Edible mushrooms and fungal biotechnology’ turns to the ways fungi are used to improve our lives. The pleasure of eating wild mushrooms, tempered with awareness of the poisonous nature of a few species, is an ancient experience born from our prehistory as hunter-gatherers in forest ecosystems. Cultivation of edible mushrooms is one of the oldest biotechnological uses of fungi, although brewing and baking with yeast go back further. In modern times, fungi are used to produce antibiotics, cyclosporin, and other medicines. Fungi are a source of industrial enzymes and acids, and the use of fungi in biofuel production is one of the most exciting ventures in modern biotechnology.

The diversity of the mycological world is far greater than most people imagine. Tens of thousands of fungal species have been described and many more are known only from the abundance of their genes in soil and water. Fungi are hugely important as agents of wood decay in forests, and, as parasites, they have caused the deaths of millions of people by ravaging crops and reshaping natural ecosystems. Fungi perform essential functions in ecosystems, and are important to both agriculture and biotechnology. Fungi: A Very Short Introduction highlights the variety and extraordinary natures of fungi, revealing the remarkable facts of fungal biology and the global significance of these enchanting organisms.

The Fungi are an ancient and diverse group of eukaryotic microoganisms. Molecular experiments suggest that the common ancestor of the fungi lived in the Precambrian. The earliest fungi were probably aquatic species whose zoospores propelled themselves through water using single flagella. Fungi called chytrids that are found in aquatic habitats and soils today may resemble these ancestral microbes. The exploration of the evolutionary relationships between different groups of fungi using molecular phylogenetic methods has produced a rich natural classification that embraces six phyla. These modern approaches to fungal classification have built upon a rich tradition of observational research that began in the eighteenth century. In this opening chapter, we consider the structural characteristics and life cycles of the major groups of fungi. This serves as an introduction to the examination of the great sweep of specific topics in fungal biology in subsequent chapters.

‘Fungal mutualisms’ considers symbiotic relationships in which the fungus and its partner benefit from their biological interaction. Examples of mutualisms with insects include fungi that trap scale insects, fungi cultivated by ambrosia beetles, and leaf-cutter ants and termites that grow mushroom gardens. These highly developed relationships involve substantial structural, biochemical, and behavioural adaptations in the fungi and insects. Fungi in mycorrhizal associations with plants operate as accessory root systems for plants, whereas fungi called endophytes house themselves inside plant tissues without any connection to an external mycelium. Lichens—composite organisms produced by a fungus and a single-celled alga or cyanobacterium—are the best-known mutualisms involving fungi.

Parasitic fungi that grow on plants have reshaped the biosphere and caused the deaths of millions of people since the beginning of agriculture. Dutch elm disease and chestnut blight are examples of fungal pandemics that resulted in widespread ecological changes in the 20th century. Crop failures caused by fungi have caused starvation, economic collapse, social conflict, warfare, and mass emigration. As the human population swells, scientists are engaged in a global effort to understand and combat fungal diseases of cereals and other vital crops. ‘Fungi as parasites of plants’ considers different types of parasitic fungi, including rusts and smuts, and their control with fungicides.

‘What is a fungus?’ explores the evolutionary origins of fungi and how they differ from plants and animals. The fungi are united by three principal characteristics: they are eukaryotes, which feed by absorption, and reproduce by forming spores. Fungi are more closely related to animals than they are to plants; fungi and animals both belong to the Opisthokonta taxonomic supergroup. The emergence of the fungi as a distinctive group of organisms is estimated to have happened between 760 million years ago and one billion years ago. The structure, growth, and physiology of the fungal cell are also described.

‘Fungi in animal health and disease’ considers the fungi that populate the healthy human microbiome and the nature of superficial and systemic fungal infections in humans and other animals. Most of our associations with fungi are harmless and some of them support our well-being. Fungal diseases or ‘mycoses’ can develop, however, when our immune defences are weakened. The resulting opportunistic infections can be difficult to treat. Infections can also develop when the skin is damaged by a severe burn or if fungi contaminate tissues exposed during surgery. Fungal spores carry allergens and are a significant cause of asthma. A small number of mushroom species produce hallucinogens and others contain poisons.

Fungi that do not form supportive or parasitic relationships with plants and animals feed on the debris of life. These are saprotrophs that decompose dead roots, leaves, flowers, fruits, seeds, twigs, branches, upright tree trunks, and fallen logs. Wood is decomposed by a combination of white rot and brown rot basidiomycetes that produce mushrooms. Other fungi grow on animal faeces and decompose the tissues of dead invertebrates and vertebrates. Fungi also clear up our mess, breaking down every natural product used in a lifetime of consumerism and destroying synthetic materials made by industry. ‘Fungi and decomposition’ describes the saprotrophic fungi and considers their significance in the global carbon cycle.

All of the structures produced by fungi, from simple budding yeast cells to long-lived bracket mushrooms, are encoded in genes. The genome of the fungus is a blueprint for its organization and operation. ‘Fungal genetics and life cycles’ explores the sequencing of genomes and progress in understanding the molecular mechanisms that link gene expression to fungal growth and development. Genetic experiments on yeast have led to major advances in our understanding of cell division and cancer. Filamentous fungi are also important research subjects for geneticists. The life cycles of mushrooms are complex and some species have thousands of mating types, or sexes.

Fungi share most fundamental features of cell structure and function with other eukaryotes. Cell biological distinctions include the unique chemical composition of the fungal cell wall and plasma membrane, and the peculiar mechanisms of hyphal growth in filamentous fungi and budding in yeasts. Filamentous fungi generate multicellular colonies, or mycelia, through the extension and repeated branching of cells called hyphae. Mycelia can be restricted to a patch on a decomposing leaf, or span an enormous territory in a forest ecosystem. Fungi also produce multicellular organs that function in the exploration of the environment and survival under conditions of environmental stress. Fruit bodies, including the familiar mushrooms of basidiomycetes, are multicellular reproductive organs. Mushroom formation involves the coordinated growth of millions of hyphae. The molecular control of hyphal growth and fruit body formation are areas of active research, but many questions about the developmental biology of the fungi are unanswered.

Fungal diversity is revealed in the study of the size and shape of spores, their development, functions, and mechanisms of dispersal. The study of spores is a study of evolution. Asexual spores include conidia and sporangiospores. Sexual spores include basidiospores, ascospores and zygospores. Many spores are dispersed from their parent colonies passively by airflow and raindrops. Other fungi employ a range of biomechanical devices to launch their spores into the air. These include pressurised squirt guns, explosive stalks, and a catapult powered by surface tension. These mechanisms produce some of the fastest movements in nature. Through a combination of passive and active mechanisms of dispersal, fungi release millions of tons of spores into the atmosphere every year. These microscopic particles are a significant cause of allergy and may affect weather patterns. Spores that develop in aquatic habitats include star-shaped conidia and the swimming spores of chytrids and other aquatic fungi.

In our time, advances in biotechnology have enabled scientists to develop industrial processes for manufacturing enzymes, organic acids, vitamins, antibiotics, and a range of other pharmaceutical agents using fungi. The use of yeasts in winemaking, brewing beer, and baking are examples of biotechnology that began thousands of years ago. Mushroom cultivation, particularly the tradition of raising mushrooms on logs, has also been practiced for centuries. Fungi are used in the manufacture of cheeses, chocolate, and a range of fermented foods. Technological advances in the design of fermenters for growing fungi, along with the development of methods of genetic transformation have revolutionised the business of fungal biotechnology. The use of fungi in biofuel production is an exceedingly important enterprise in an era of climate change and the recognition of its link to burning fossil fuels. Fungi also show promise in the remediation of habitats damaged by industrial activity, mining, and agriculture.

Conidial dispersal in Stachybotrys chartarum in response to low-velocity airflow was studied using a microflow apparatus. The maximum rate of spore release occurred during the first 5 min of airflow, followed by a dramatic reduction in dispersal that left more than 99% of the conidia attached to their conidiophores. Micromanipulation of undisturbed colonies showed that micronewton (microN) forces were needed to dislodge spore clusters from their supporting conidiophores. Calculations show that airspeeds that normally prevail in the indoor environment disturb colonies with forces that are 1000-fold lower, in the nanonewton (nN) range. Low-velocity airflow does not, therefore, cause sufficient disturbance to disperse a large proportion of the conidia of S. chartarum.

Stipe elongation in fruit bodies of Coprinopsis cinerea (syn. Coprinus cinereus) was examined from a biomechanical perspective. Two strains were studied: the self-compatible Amut Bmut homokaryon that produces normal fruit bodies with relatively short stipes, and mutant B1918 that produces abnormally elongated stipes. Measurements of the pressure exerted by developing mushrooms were made using strain gauges, and these data were compared with measurements of the pressures exerted by vegetative hyphae of the same strains. The experiments demonstrate that AmutBmut hyphae elongating within stipe tissue push with the same pressure (approx. 0.5 atmosphere) as vegetative hyphae growing through their food sources. In purely biomechanical terms, the fruit body may therefore be viewed as a relatively uncomplicated sum of its parts. Analysis of the mutant strain B1918 demonstrated that hyperelongation of the stipe is not associated with any difference in the pressure exerted by the fruit body. The fault in the mechanism of stipe extension in B1918 may be reflected in the increased fluidity of the cell wall of vegetative hyphae of this strain, but further work is necessary to resolve this.

Invasive hyphal growth allows filamentous fungi to insinuate themselves in the solid materials that serve as their food sources. Hyphae overcome the mechanical resistance of plant and animal tissues, and other substances through the secretion of digestive enzymes and the exertion of force. This force is derived from the osmotically-generated turgor pressure within the hypha and is governed by wall loosening at the growing apex. This article offers a concise description of the biomechanics of this process.

Microbiological research has been dominated by studies on pathogenic organisms since the work of Louis Pasteur in the 19th century. Recent research suggests that populations of microbes that live in our digestive, reproductive, and respiratory tracts are as important to our wellbeing as the avoidance and treatment of infection. The average human comprises 40 trillion eukaryotic cells and an accompanying microbiome of 100 trillion bacteria, mostly in the gut, and one quadrillion viruses. In addition to bacteria and viruses, the microbiome contains archaea, plus fungi and other eukaryotic microorganisms. The majority of these microbes are beneficial and only a minority have the potential to cause disease.

‘Microbial diversity’ considers the vast array of microorganisms—the smallest forms of life—which exist everywhere. The three primary groups of microorganisms are bacteria, archaea, and eukaryotes. Bacteria and archaea are prokaryotes with their genetic material held in a single chromosome. In eukaryotes, most of the genome is held in multiple chromosomes. Over 11,000 species of bacteria have been identified using microscopic identification of cell shape and metabolic activity, Gram-staining techniques, and genetic identification of RNA and DNA sequences. There are 500 named species of archaea, divided into two phyla: the euryarchaeota and the crenarchaeota. There are eight supergroupings of eukaryotes, all of them include single-celled organisms, and five are entirely microbial.

‘How microbes operate’ considers the mechanisms that sustain prokaryotic and eukaryotic microorganisms. All active cells must be supplied with water and an energy source. Absorption of water is essential, even in extremely dry or salty habitats, because the enzymes that catalyse biochemical reactions in cells do not work unless they are hydrated. Sunlight powers the metabolism of photosynthetic microbes and others glean chemical energy from a plenitude of terrestrial sources. Extremes in temperature, acidity, and other environmental variables place additional constraints upon microbial life, but bacteria, archaea, and eukaryotic microorganisms thrive in most places where liquid water is available.

‘Microbes in agriculture and biotechnology’ considers the applied microbiological research to improve soil fertility and combat plant diseases, as well as the development of genetically modified (GM) food, which may help to reduce the cost of modern agricultural practices and their contribution to climate change. Natural mechanisms that control soil fertility are inadequate to the task of supporting modern intensive agriculture and a human population that may exceed nine billion in 2050. Intensive grazing of cattle on deforested land is similarly unsustainable. Even in areas where soils are exceedingly rich, crop productivity falls without soil amendment with organic matter and inorganic fertilizers.