Fungi eat by secreting enzymes out of the tips of their hyphae. Instead of engulfing food like an amoeba or ingesting and digesting it like an animal, they dump enzymes onto the food itself and after it breaks down into smaller molecules, they suck it back up through their hyphae. The ones that can break down cellulose are the ones that grow on plants or plant matter; the ones that break down keratin grow well on skin or hair or hooves. Because of their eating style, fungi are the Great Decomposers, regardless of whether they're a mushroom on the ground, a bracket on a tree, a puffball, a plant pathogen or a film of mold on the wall of the forgotten tub of yogurt in the back of your refrigerator.
There are several different phyla of fungi, but most of the ones we're familiar with fit into one of two of them: Basiodiomycota and Ascomycota. The phylum that houses most of the fungi we think of as "mushrooms" is the basiodiomycota — they're in the grocery store, making "fairy rings" in your yard, shelves on trees and sometimes causing plant diseases.
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Most of these have fruiting bodies that spring up from the mycelium inside a dead log or under the soil — in fact, the mycelium is where most of the mushroom business gets done, so a lot of the organism itself is always out of sight. What we think of as the "mushroom" is just the reproductive structure that the fungus sends up to release spores.
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Once a spore lands, the hyphae start growing out in all directions from the place the spore landed, which is why mushrooms often grow in a ring formation. The other group of fungi you would recognize is the ascomycota. Most molds, for instance, are in this phylum: they usually don't produce a large mushroom — they grow in circles like all fungi, so if you leave your coffee out for a few days, you'll notice the mold grows radially out from a single point.
Yeasts, morel mushrooms, truffles and cup fungi are in this group. These organisms are eukaryotes that have a nucleus with a nuclear envelope, an intracytoplasmic membrane system, chromosome separation on mitotic spindles, vesicular Golgi, and a mitochondrial remnant organelle lacking a genome termed a mitosome 4. For insects, fish, laboratory rodents, and rabbits microsporidia are important pathogens, and they have been investigated as biological control agents for destructive species of insects 2. Several species of microsporidia have caused significant agricultural economic losses including Nosema apis and Nosema ceranae in honeybees 5 , Loma salmonae in salmonid fish 6 , and Thelohania species in shrimp 7.
Franzen 8 published an excellent review of the history of research on these pathogens, and a recent textbook by Weiss and Becnel 2 provides a comprehensive examination of what is known about these organisms. In Sprague elevated the class or order Microsporidia to the phylum Microspora 9 , and a decade later Sprague and Becnel 10 suggested that the term Microsporidia should instead be used for the phylum name. Major subphyla include the Taphrinomycotina e. Most Saccharomycotina grow as budding yeast or are dimorphic can grow as yeast or filaments , whereas most Pezizomycotina are predominantly filamentous, although some are also dimorphic.
In the phylum Basidiomycota, a wide variety of lifestyles are represented. These range from well-known and conspicuous wood-decaying mushrooms, plant growth-promoting and mutualistic mycorrhizae, and crop-destroying smut and rust fungi, to yeast-like human pathogens. For over a century fungi have been recognized as having diverse breeding systems, from homothallism i. The study of breeding systems, for example, led to the discovery of the astounding variability in mating-type alleles among mushrooms, with thousands of different mating types in some species 1 , and to the realization that in many fungal pathogens the process of sexual reproduction is closely linked to infection and pathogenicity 2 Fig.
The importance of basidiomycete fungi and their great research tractability, from ecology to genomics, have brought major insights into the diversification of genetic mechanisms used to achieve sexual reproduction. The Mucoromycota is a newly formalized phylum of fungi that are one of what are sometimes considered the basal lineages in the fungi 1. These species have undergone a different evolutionary trajectory than the Ascomycetes and Basidiomycetes. Generally, the species are difficult to develop into experimental models, but despite this our understanding of mating and sex in the fungi overall has been punctuated with major discoveries being made in this lineage.
Sexual reproduction is a ubiquitous feature of the eukaryotic kingdom with the many benefits of sex in generating genetic diversity as substrates for evolutionary selection being well known.
When two different partners come together, there is the generation of genetic variation in the offspring, through the processes of crossover and recombination during meiosis, enabling response of future generations to environmental selection pressures 1 — 4. Sexual reproduction also allows the repair of random epigenetic or conventional genetic damage by recombination with homologous chromosomes and can mask lethal mutations 4 , 5.
In addition, sexual recombination alleviates clonal interference and prevents deleterious mutations hitchhiking to fixation 6. As a result, supposed ancient asexual species such as the bdelloid rotifers an exclusively female class of over rotifer species thought to date back several million years and darwinulid ostracods a family of around 30 crustacean species thought to have been exclusively female and asexual for over million years, but for which very rare living males have recently been described have gained notoriety 8 — This is despite the fact that sexual reproduction in fungi can have additional benefits such as the production of fruit bodies and sexual spores that are resistant to adverse environmental conditions, thereby promoting survival of sexual offspring; it can provide a transient diploid arena for selection of genes; and sex can favorably impact genome evolution 14 — Cell-cell fusion is an essential biological process that occurs in organisms throughout the tree of life.
It is involved in both sexual and asexual developmental processes in most species and has been shown to occur in multicellular and in unicellular organisms. Somatic cell fusion events are widespread in eukaryotic organisms, including animals, where they are important for muscle differentiation, placental development, and formation of multinucleate giant cells in the immune system 1 — 4. Filamentous fungi are a large and ancient clade of microorganisms that occupy a broad range of ecological niches 1 , 2. However, fungi pose a threat to public health, the ecosystem, and our food security 6 , 7.
The success of filamentous fungi is largely due to their elongate hypha, a chain of cells separated from each other by septa 8. Hyphae grow rapidly by polarized exocytosis at the apex 9 — 11 , which allows the fungus to extend over long distances and invade many substrates, including soils and host tissues.
Triumph of the Fungi: A Rotten History
Hyphal tip growth is initiated by establishment of a growth site and the subsequent maintenance of the growth axis, with transport of growth supplies, including membranes and proteins, delivered by motors along the cytoskeleton to the hyphal apex Among the enzymes delivered are cell wall synthases that are exocytosed for local synthesis of the extracellular cell wall Exocytosis is opposed by endocytic uptake of soluble and membrane-bound material into the cell The first intracellular compartment in the endocytic pathway is the early endosomes EEs , which emerge to perform essential additional functions as spatial organizers of the hyphal cell Individual compartments within septated hyphae can communicate with each other via septal pores, which allow passage of cytoplasm or organelles 16 to help differentiation within the mycelium This article introduces the reader to more detailed aspects of hyphal growth in fungi.
Fungal cell walls are dynamic structures that are essential for cell viability, morphogenesis, and pathogenesis. The wall is much more than the outer layer of the fungus; it is also a dynamic organelle whose composition greatly influences the ecology of the fungus and whose composition is highly regulated in response to environmental conditions and imposed stresses. A measure of the importance of the cell wall can be appreciated by the fact that approximately one-fifth of the yeast genome is devoted to the biosynthesis of the cell wall 1 , 2.
Of these approximately 1, Saccharomyces cerevisiae genes 2 , some are concerned with the assembly of the basic components, others provide substrates for wall materials, and many regulate the assembly process and couple this to environmental challenges.
Many of the building blocks of the cell wall are conserved in different fungal species 4 , while other components of the wall are species-specific, and there is perhaps no part of the cell that exhibits more phenotypic diversity and plasticity than the cell wall. Decomposer fungi, by their very nature, continually deplete the organic resources in which they grow and feed. They therefore rely on continual successful spread to new resources. In terrestrial ecosystems resources are distributed heterogeneously in space and time 1 , 2.
They are often discrete, ranging in size from small fragments, e. The processes of arrival and spread are thus crucial to the success of saprotrophic fungi. Following arrival at a resource, their competitive ability determines whether they are successful in colonization and how long they retain that territory.
Colonization and competition are the main focus of this paper and are discussed separately below, largely drawing on wood decay fungi for illustrative examples. The relative degree to which organisms move is a process operating at multiple temporal and physical scales 1. In recent years dispersal has received a great deal of attention in fields ranging from mathematics and physics to ecology and molecular biology, but only a patchy framework exists to explain dispersal over very large distances.
Modeling patterns of long-distance dispersal LDD among macroorganisms, ranging from vertebrates and flying insects to seed plants, appears tractable, but documenting the geographic distributions and dispersal dynamics of microscopic propagules and microbes presents multiple theoretical and methodological challenges 2 — 4. The majority of empirical research directly measuring the dispersal of microbes or microscopic propagules is restricted to relatively short distances, and tracking dispersal at greater spatial scales involves mathematical or genetic models, e. However, fitting dispersal data e.
Inferences based on population genetics data capture rare instances of successful LDD but incompletely describe underlying demographic processes and typically cannot speak to mechanisms of LDD 1. Besides the limitations of mathematical and genetic methods, important details about the natural history of species are often ignored or remain unknown, leaving many questions unanswered, including, e. Growth as an interconnected mycelial network is characteristic of filamentous fungi and has been subject to scientific investigation since the seminal works of Buller at the start of the 20th century 1 — 3.
We have increasingly detailed understanding of the fundamental cellular processes needed to form a network, such as hyphal tip growth 4 , septation 5 , 6 , hyphal orientation 7 , branching 8 , and fusion 9 — 13 Fig. In contrast, we know far less about the molecular events at the next physical scale that leads to hyphal aggregation and hyphal differentiation, and how these impact physiological processes such as long-distance resource distribution and biomass recycling.
For example, while direct uptake and intrahyphal nutrient diffusion may be sufficient to sustain short-range local growth when resources are abundant 14 , long-distance translocation is required to deliver nutrients at a sufficient rate to growing tips, particularly in fungi that form large networks on the forest floor that are too large to distribute nutrients through diffusion alone. We know little about the quantitative contribution of different potential transport pathways, such as cytoplasmic streaming, vesicle transport, growth-induced mass flow, or evaporative mass flow, to net fluxes and overall nutrient dynamics, and how they might vary between species and developmental stage 15 — Nevertheless, the behavior of the growing mycelial network emerges from the interaction of many such processes and requires an integrated view to understand the overall impact on fungal behavior 18 — Our understanding is further constrained by inferences drawn from a limited number of genetically tractable model filamentous species grown under laboratory conditions abundant, evenly dispersed, low-molecular-weight resources, high relative humidity, constant light and temperature compared with real-world conditions patchy, recalcitrant, ephemeral resources, fluctuating temperature, light and relative humidity.
The significance of fungi in natural environments is extensive and profound. Their most obvious roles are as decomposers of organic materials and as animal and plant pathogens and symbionts. It is therefore obvious that they are of major importance in the global carbon cycle through such activities and as important determinants of plant growth and productivity. However, their importance in terms of nutrient and element cycling greatly extends beyond these core activities, and they are involved in the biogeochemical cycling of many other elements and substances, as well as many other related processes of environmental significance.
The growing discipline of geomicrobiology addresses the roles of microorganisms in geological and geochemical processes 1 , 2 , and geomycology can be considered to be a part of this topic that focuses on the fungi 3 , 4. The often clear demarcation between mycological and bacteriological research has ensured that the geoactive properties and significance of fungi have been unappreciated in wider geomicrobiological contexts.
The range of prokaryotic metabolic diversity found in archaea and bacteria, including their abilities to use a variety of different terminal electron acceptors in respiration and effect redox transformations of many metal species 5 , 6 , has also contributed to a narrow overall view of the significance of eukaryotic organisms in important biosphere processes.
Nevertheless, appreciation of fungi as agents of geochemical change is growing, and their significance is being discovered even in locations not usually regarded as prime fungal habitats, e. Their significance as bioweathering agents of rocks and minerals is probably better understood than bacterial roles 12 , and this ability is of prime importance in the weathering of human structures in the built environment and cultural heritage 13 — On the positive side, the geoactive properties of fungi can be used for human benefit, and several aspects may contribute to providing solutions to several important global challenges.
Geomycology is relevant to reclamation and revegetation of polluted habitats, bioremediation, nuclear decommissioning and radionuclide containment, biorecovery of important elements, and the production of novel biomaterials.
Characteristics of Fungi | Boundless Biology
This chapter outlines important geoactive properties of fungi in relation to important environmental processes, their positive and negative applications, and their impact on human society. Plant pathogens are parasites that live at the expense of their host. While fungal pathogens are the largest group of plant pathogens, other important plant pathogens include bacteria, protists, chromists, nematodes, and even plants.
Although this wide variety of pathogens share many aspects in epidemiology and management, here we deal only with fungal plant pathogens. The economic importance of fungal plant pathogens in the production of food, feed, materials, and ornamentals is undisputed 1. Direct costs include yield loss and use of resistant cultivars or pesticides.
Indirect costs include the inability to grow certain crops or cultivars at a given location. Inspection and quarantine protocols to prevent the dispersal of pathogens 2 are indirect costs that are rarely taken into account. In contrast, as will be shown in this review, plant pathogens in nature are regarded as crucial contributors to the maintenance of biodiversity, similar to the role major animal predators play in wildlife.
There is molecular and structural evidence that the aquatic phycomycetes is a diverse, polyphyletic assemblage of species. For many years little research has been conducted with the aquatic phycomycetes, possibly because they were thought to be ecologically and commercially insignificant, but this perception has recently changed.
Many of these species have been found to play key roles in biomass conversion in food webs Fig. To respond to the changing environment, cells must be able to sense external conditions.
This is important for many processes including growth, mating, the expression of virulence factors, and several other regulatory effects. Nutrient sensing at the plasma membrane is mediated by different classes of membrane proteins that activate downstream signaling pathways: nontransporting receptors, transceptors, classical and nonclassical G-protein-coupled receptors, and the newly defined extracellular mucin receptors. Nontransporting receptors have the same structure as transport proteins, but have lost the capacity to transport while gaining a receptor function.