Week 2 - Domains Bacteria and Archae - PDF

Week 2 Domains Bacteria and Archae Protist Kingdom Fungi Lab: Cell Structure  Objectives 1. Describe the basic features of all prokaryotes. 2. Describe the variation that prokaryotes possess regarding their nutritional and metabolic adaptations. 3.Describe the unique charact...

Week 2 Domains Bacteria and Archae Protist Kingdom Fungi Lab: Cell Structure  Objectives 1. Describe the basic features of all prokaryotes. 2. Describe the variation that prokaryotes possess regarding their nutritional and metabolic adaptations. 3.Describe the unique characteristics of the Domain Archae. 4. Describe the roles that bacteria play in the biosphere and their harmful and beneficial impacts on humans. 1. Describe the basic features of prokaryotes. Overview: Masters of Adaptation Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms Most prokaryotes are microscopic, but what they lack in size they make up for in numbers There are more in a handful of fertile soil than the number of people who have ever lived A diagrammatic representation of the relative sizes of viruses, bacteria, and eukaryotic cells.  They have an astonishing genetic diversity Prokaryotes are divided into two domains: bacteria and archaea Why does this toxic tailing pond emit methane Structural and functional adaptations contribute to prokaryotic success Prokaryotes are unicellular, although some species form colonies Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells Prokaryotic cells have a variety of shapes The three most common shapes are spheres (cocci), rods (bacilli), and spirals  The most common shapes of prokaryotes 1 µm 2 µm 5 µm (a) Spherical (b) Rod-shaped (c) Spiral (cocci) (bacilli)  Cell-Surface Structures An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides Eukaryote cell walls are made of cellulose or chitin  Archaea contain polysaccharides and proteins but lack peptidoglycan Using the Gram stain, scientists classify many bacterial species into Gram-positive and Gram- negative groups based on cell wall composition Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant Many antibiotics target peptidoglycan and damage bacterial cell walls (e.g. penicillin) A polysaccharide or protein layer called a capsule covers many prokaryotes Capsule  The prokaryotic genome has less DNA than the eukaryotic genome Most of the genome consists of a circular chromosome The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region Some species of bacteria also have smaller rings of DNA called plasmids Chromosome Plasmids 1 µm  Prokaryotes can evolve rapidly because of their short generation times Prokaryotes have NO membrane bound organelles 2. Describe the variation that prokaryotes possess regarding their nutritional and metabolic adaptations The Role of Oxygen in Metabolism Prokaryotic metabolism varies with respect to O 2: – Obligate aerobes require O2 for cellular respiration – Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration – Facultative anaerobes can survive with or without O2  Nitrogen Metabolism Prokaryotes can metabolise nitrogen in a variety of ways In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) Nitrogen fixation is vital for the growth of many plants. These bacterial nitrogen fixers provide nitrogen in a form that these plants can use. They also form symbiotic relationships with these plants.  Metabolic Cooperation Cooperation between prokaryotes allows them to use environmental resources they could not use as individual cells In the cyanobacterium Anabaena, photosynthetic cells and nitrogen-fixing cells called heterocytes exchange metabolic products Metabolic cooperation in a colonial prokaryote Photosynthetic cells Heterocyte 20 µm  Some sulphate-consuming bacteria are known to coexist with methane-consuming archaea in the form of aggregates laying on the ocean floor. The bacteria use the waste material of the archaea to produce hydrogen and carbon containing compounds. The archaea gain benefit from the production of sulphur containing compounds by the bacteria which they can use as an oxidizing agent in a methane environment devoid of oxygen. In some prokaryotic species, metabolic cooperation occurs in surface-coating colonies called biofilms (e.g. plaque) 1 µm 3.Describe the unique characteristics of the Domain Archae. Archaea Archaea share certain traits with bacteria and other traits with eukaryotes  Some archaea live in extreme environments and are called extremophiles Extreme halophiles live in highly saline environments Extreme thermophiles thrive in very hot environments Extreme thermophiles  Methanogens live in swamps and marshes and produce methane as a waste product Methanogens are strict anaerobes and are poisoned by O2 In recent years, genetic prospecting has revealed many new groups of archaea Some of these may offer clues to the early evolution of life on Earth 4. Describe the roles that bacteria play in the biosphere and their harmful and beneficial impacts on humans. Prokaryotes play crucial roles in the biosphere Prokaryotes are so important to the biosphere that if they were to disappear the prospects for any other life surviving would be dim  Chemical Cycling Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems Chemoheterotrophic prokaryotes function as decomposers, breaking down corpses, dead vegetation, and waste products Nitrogen-fixing prokaryotes add usable nitrogen to the environment  Prokaryotes can sometimes increase the availability of nitrogen, phosphorus, and potassium for plant growth Prokaryotes can also “immobilize” or decrease the availability of nutrients Impact of bacteria on soil nutrient availability 1.0 Uptake of K by plants (mg) 0.8 0.6 0.4 0.2 0 No Strain 1 Strain 2 Strain 3 bacteria Soil treatment  Ecological Interactions Symbiosis is an ecological relationship in which two species live in close contact: a larger host and smaller symbiont Prokaryotes often form symbiotic relationships with larger organisms Various forms of symbiosis exist  In mutualism, both symbiotic organisms benefit In commensalism, one organism benefits while neither harming nor helping the other in any significant way In parasitism, an organism called a parasite harms but does not kill its host Parasites that cause disease are called pathogens Impact: The Human Microbiome and Health  Prokaryotes have both harmful and beneficial impacts on humans Pathogenic Prokaryotes Some prokaryotes are human pathogens, but others have positive interactions with humans Prokaryotes cause about half of all human diseases Lyme disease is an example Lyme disease Deer tick  Lyme disease 5 µm 5 µm Borrelia burgdorferi (SEM) Lyme disease rash  Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins Exotoxins cause disease even if the prokaryotes that produce them are not present Endotoxins are released only when bacteria die and their cell walls break down Many pathogenic bacteria are potential weapons of bioterrorism Summary of the roles of eubacteria (bacteria) decomposers food source some are symbiotic (help their hosts) some cause disease some are autotrophic produce oxygen some fix nitrogen Prokaryotes in Research and Technology Experiments using prokaryotes have led to important advances in DNA technology Prokaryotes are the principal agents in bioremediation, the use of organisms to remove pollutants from the environment  Some other uses of prokaryotes: – Recovery of metals from ores – Synthesis of vitamins – Production of antibiotics, hormones, and other products  Bacteria making PHA. Can be used to make plasticsl (b) (c) (a) Bacteria making ethanol can be used as fuel Some bacteria can metabolise oil  Protista Objectives 1. Describe the current hypothesis of the origin of eukaryotes 2. Describe the nature of eukaryotic diversity including the significance of the term protist and the position of the multicellular Kingdoms (animalia, plantae, fungae) within the currently accepted phylogeny of the eukaryotes 3. Describe the diversity of cellular structure, nutritional mode and reproduction found among the protists. 4. Describe the distinguishing characteristics and biology of the example protists Euglena, Paramecium, brown, red and green algae, slime molds and Amoeba. 5. Describe the ecological roles that protists play in the biosphere 1. Describe the current hypothesis of the origin of eukaryotes The First Eukaryotes The hypothesis of endosymbiosis proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells An endosymbiont is a cell that lives within a host cell  The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites In the process of becoming more interdependent, the host and endosymbionts would have become a single organism Serial endosymbiosis supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events A model of the origin of eukaryotes through serial endosymbiosis Cytoplasm Plasma membrane Ancestral DNA prokaryote Endoplasmic reticulum Nucleus Nuclear envelope Aerobic heterotrophic prokaryote Mitochondrion Ancestral heterotrophic eukaryote  Photosynthetic prokaryote Mitochondrion Plastid Ancestral photosynthetic eukaryote  Cytoplasm Plasma membrane Ancestral DNA prokaryote Endoplasmic reticulum Nucleus Nuclear envelope Aerobic heterotrophic Photosynthetic prokaryote prokaryote Mitochondrion Ancestral Mitochondrion heterotrophic eukaryote Plastid Ancestral photosynthetic eukaryote  Key evidence supporting an endosymbiotic origin of mitochondria and plastids: – Similarities in inner membrane structures and functions – Division is similar in these organelles and some prokaryotes (binary fission) – These organelles transcribe and translate their own DNA – Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes – Sensitivity to some antibiotics  Endosymbiosis in Eukaryotic Evolution There is now considerable evidence that much protist diversity has its origins in endosymbiosis Mitochondria evolved by endosymbiosis of an aerobic prokaryote (an alpha proteobacterium) Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium  It is believed that animal & fungal cells arose from ancestral protists that did not engulf cyanobacteria after mitochondria and therefore these organisms remained heterotrophic Plants cells may have arisen from photosynthetic protists containing plastids Diversity of plastids produced by secondary Plastid endosymbiosis Dinoflagellates Secondary endosymbiosis Apicomplexans Cyanobacterium Red alga Primary endosymbiosis Stramenopiles Heterotrophic Secondary Plastid endosymbiosis eukaryote Over the course of evolution, this membrane Euglenids was lost. Secondary endosymbiosis Green alga Chlorarachniophytes  The plastid-bearing lineage of protists evolved into red algae and green algae On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote 2. Describe the nature of eukaryotic diversity including the significance of the term protist and the position of the multicellular Kingdoms (animalia, plantae, fungae) within the currently accepted phylogeny of the eukaryotes  Living Small Protist is the informal name of the kingdom of mostly unicellular eukaryotes Advances in eukaryotic systematics have caused the classification of protists to change significantly Protists constitute a paraphyletic group, and Protista are no longer valid as a kingdom Most eukaryotes are single-celled organisms Protists are eukaryotes and thus have organelles and are more complex than prokaryotes Most protists are unicellular, but there are some colonial and multicellular species 3. Describe the diversity of cellular structure, nutritional mode and reproduction found among the protists. Structural and Functional Diversity in Protists Protists exhibit more structural and functional diversity than any other group of eukaryotes Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell  Protists, the most nutritionally diverse of all eukaryotes, include: – Photoautotrophs, which contain chloroplasts – Heterotrophs, which absorb organic molecules or ingest larger food particles – Mixotrophs, which combine photosynthesis and heterotrophic nutrition Protists can reproduce asexually or sexually, or by the sexual processes of meiosis and syngamy Four Supergroups of Eukaryotes  Diplomonads and Parabasalids These 2 groups live in anaerobic environments, lack plastids, and have modified mitochondria Diplomonads – Have modified mitochondria called mitosomes – Derive energy anaerobically, for example, by glycolysis – Have two equal-sized nuclei and multiple flagella – Are often parasites, for example, Giardia intestinalis Parabasalids – Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically – Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females  Giardia intestinalis: a diplomonad parasite 5 µm  Flagella The parabasalid Trichomonas vaginalis (colourised SEM) Undulating membrane 5 µm  Chromalveolata: a diatom 50 µm  20 µm Globigerina: a foram in the supergroup of protists- Rhizaria  20 µm 50 µm Volvox: a colonial freshwater algae  A unikont amoeba 100 µm  Euglenozoans Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites The main feature distinguishing them as a clade is a spiral or crystalline rod of unknown function inside their flagella This clade includes the kinetoplastids and euglenids  Kinetoplastids Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast They include free-living consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems This group includes Trypanosoma, which causes sleeping sickness in humans Another pathogenic trypanosome causes Chagas’ disease Trypanosoma, the kinetoplastid that causes sleeping sickness 9 µm  Dinoflagellates Dinoflagellates are a diverse group of aquatic mixotrophs and heterotrophs They are abundant components of both marine and freshwater phytoplankton Each has a characteristic shape that in many species is reinforced by internal plates of cellulose Toxic “red tides” have been known to be caused by blooms of dinoflagellates Pfiesteria shumwayae, a dinoflagellate Flagella 3 µm  Apicomplexans Apicomplexans are parasites of animals, and some cause serious human diseases One end, the apex, contains a complex of organelles specialized for penetrating a host They have a nonphotosynthetic plastid, the apicoplast Most have sexual and asexual stages that require two or more different host species for completion The two-host cycle of Plasmodium, the apicomplexan that causes malaria Inside mosquito Inside human Merozoite Sporozoites (n) Liver Liver cell Oocyst Apex MEIOSIS Red blood Merozoite cell (n) Zygote Red blood (2n) cells FERTILIZATION Gametes Gametocytes Key (n) Haploid (n) Diploid (2n)  Diatoms Diatoms are unicellular algae with a unique two- part, glass-like wall of hydrated silica Diatoms usually reproduce asexually, and occasionally sexually A freshwater diatom (colourised SEM) 3 µm Rhizarians are a diverse group of protists defined by DNA similarities DNA evidence supports Rhizaria as a monophyletic clade Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria Rhizarians include forams and radiolarians Pseudopodia A radiolarian 200 µm 4. Describe the distinguishing characteristics and biology of the example protists Euglena, Paramecium, brown algae, slime moulds and Amoeba. Euglenids Euglenids have one or two flagella that emerge from a pocket at one end of the cell Some species can be both autotrophic and heterotrophic  Euglena, a euglenid commonly found in pond water Long flagellum Eyespot Short flagellum Light detector Contractile vacuole Nucleus Chloroplast Plasma membrane Pellicle Euglena (LM) 5 µm  Ciliates Ciliates, a large varied group of protists, are named for their use of cilia to move and feed They have large macronuclei and small micronuclei  Contractile vacuole Oral groove Cell mouth Cilia 50 µm Micronucleus Food vacuoles Macronucleus (a) Feeding, waste removal, and water balance MEIOSIS Haploid Diploid micronucleus Compatible micronucleus mates The original Diploid macronucleus micronucleus disintegrates. MICRONUCLEAR FUSION Key (b) Conjugation and reproduction Structure and function in the ciliate Paramecium Conjugation caudatum Reproduction The Algae constitute the three primarily multicellular taxonomic groups that are classified as Protists. While all are photosynthetic, they differ in the ways shown below. Characteristic Chlorophyta Phaeophyta Rhodophyta Colour green brown red Habitat freshwater, marine and mainly marine (most primarily marine terrestrial of the organisms known as seaweeds) Photosynthetic chlorophyll a and b (as chlorophyll a and c, chlorophyll a and pigments in higher plants), accessory various variety of accessory pigments accessory pigments - xanthophylls and pigments - carotenoids fucoxanthins phycocyanins (blue-green) and phycoerythrins Form single celled to mainly multicelled multicelled (~4000 multicelled (~ 7000 (~1500 species) species) species)  Brown Algae Brown algae are the largest and most complex algae All are multicellular, and most are marine Brown algae include many species commonly called “seaweeds” Brown algae have the most complex multicellular anatomy of all algae  Giant seaweeds called kelps live in deep parts of the ocean The algal body is plantlike but lacks true roots, stems, and leaves and is called a thallus The rootlike holdfast anchors the stemlike stipe, which in turn supports the leaflike blades  Seaweeds: adapted to life at the ocean’s margins Blade Stipe Holdfast Red algae and green algae are the closest relatives of land plants Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont The photosynthetic descendants of this ancient protist evolved into red algae and green algae Land plants are descended from the green algae (charophyte group of green algae)  Red Algae Red algae are reddish in colour due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll The colour varies from greenish-red in shallow water to dark red or almost black in deep water Red algae are usually multicellular; the largest are seaweeds Red algae are the most abundant large algae in coastal waters of the tropics  Bonnemaisonia Red algae hamifera 20 cm 8 mm Dulse (Palmaria palmata) Nori. The red alga Porphyra is the source of a traditional Japanese food. The seaweed is grown on nets in shallow coastal waters. The harvested seaweed is spread on bamboo screens to dry. Paper-thin, glossy sheets of nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi.  Green Algae Green algae are named for their grass-green chloroplasts Plants are descended from the green algae The two main groups are chlorophytes and charophyceans Most chlorophytes live in fresh water, although many are marine Other chlorophytes live in damp soil, as symbionts in lichens, or in snow  (a) Ulva, or sea lettuce Multicellular chlorophytes 2 cm (b) Caulerpa, an intertidal chloro- phyte Multicellular chlorophytes  Amoebozoans Amoebozoans are amoeba that have lobe- or tube- shaped, rather than threadlike, pseudopodia They include gymnamoebas, entamoebas, and slime moulds A unikont amoeba  Slime Moulds Slime moulds, or mycetozoans, were once thought to be fungi Molecular systematics places slime moulds in the clade Amoebozoa Plasmodial Slime Moulds At one point in the life cycle, plasmodial slime moulds form a mass called a plasmodium (not to be confused with malarial Plasmodium) The plasmodium is undivided by membranes and contains many diploid nuclei It extends pseudopodia through decomposing material, engulfing food by phagocytosis  Cellular Slime Moulds Cellular slime moulds form multicellular aggregates in which cells are separated by their membranes Cells feed individually, but can aggregate to form a fruiting body The Unikonts, in general are closely related to animals and fungi in terms of possible ancestry. It is believed that animals and fungi are descended from types of opisthokonts, specifically from choanoflagelates. 5. Describe the ecological roles that protists play in the biosphere Symbiotic Protists Some protist symbionts benefit their hosts – Dinoflagellates nourish coral polyps that build reefs – Hypermastigotes digest cellulose in the gut of termites Hypermastigote, a protist symbiont: Lives in the guts of termites and allows them to digest wood  Some protists are parasitic – Plasmodium causes malaria – Pfesteria shumwayae is a dinoflagellate that causes fish kills – Phytophthora ramorum causes sudden oak death  Photosynthetic Protists Many protists are important producers that obtain energy from the sun In aquatic environments, photosynthetic protists and prokaryotes are the main producers The availability of nutrients can affect the concentration of protists Protists can be grouped according to their mode of living, i.e. unicellular, multicellular, or colonial. Protists can also be grouped according to their ecological roles in the biosphere: ROLE EXAMPLE 1. DECOMPOSER Slime molds break down rotting logs and forest litter. Water molds break down dead organic aquatic plants and animals 2. FOOD FOR ANIMALS Small animals feed on protists 3. PRODUCE OXYGEN Photosynthetic protists (e.g. Euglena) release O2, and fix carbon in the biosphere 4. CAUSE DISEASES a. Protists are significant agricultural pathogens -late potato blight causes potatoes to rot in the ground b. Some protists cause disease in animals -malaria -amoebic dysentery -Giardia c. Some protists produce toxins which are poisonous to animals -red tide is caused by the protist Gonyaulax concatenensis  Kingdom Fungi Objectives 1. Describe the key characteristics of fungi, focussing on there structure, mode of nutrition and ecology 2. Explain the current hypothesis on the evolutionary origin of fungi 3. Describe the key roles that fungi play in terms of nutrient recycling, ecological interactions and human impacts 1. Describe the key characteristics of fungi, focusing on there structure, mode of nutrition and ecology Overview: Mighty Mushrooms Fungi are diverse and widespread They are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients  Nutrition and Ecology Despite their diversity, fungi share key traits, most importantly the way in which they derive nutrition Fungi are heterotrophs and absorb nutrients from outside of their body Fungi use enzymes to break down a large variety of complex molecules into smaller organic compounds The versatility of these enzymes contributes to fungi’s ecological success Fungi exhibit diverse lifestyles: – Decomposers – Parasites – Mutualists  Body Structure The most common body structures are multicellular filaments and single cells (yeasts) Some species grow as either filaments or yeasts; others grow as both Fungal Morphology The morphology of multicellular fungi enhances their ability to absorb nutrients Fungi consist of mycelia, networks of branched hyphae adapted for absorption Most fungi have cell walls made of chitin Structure of a multicellular fungus Reproductive structure Hyphae Spore-producing structures 20 µm Mycelium  Cell wall Nuclei Cell wall Pore Nuclei Septum (a) Septate hypha (b) Coenocytic hypha Some fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of organelles Coenocytic fungi lack septa Specialised Hyphae in Mycorrhizal Fungi Some unique fungi have specialized hyphae called haustoria that allow them to penetrate the tissues of their host  Hyphae Nematode 25 µm (a) Hyphae adapted for trapping and killing prey Plant Fungal hypha cell wall Plant cell Plant cell plasma Haustorium membrane (b) Haustoria  Mycorrhizae are mutually beneficial relationships between fungi and plant roots Ectomycorrhizal fungi form sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex Arbuscular mycorrhizal fungi extend hyphae through the cell walls of root cells and into tubes formed by invagination of the root cell membrane Fungi produce spores through sexual or asexual life cycles Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually Fungi can produce spores from different types of life cycles 2. Explain the current hypothesis on the evolutionary origin of fungi The Origin of Fungi The ancestor of fungi was an aquatic, single- celled, flagellated protist Fungi and animals are more closely related to each other than they are to plants or other eukaryotes Fungi, animals, and their protistan relatives form the opisthokonts clade Fungi and their close relatives Animals (and their close protistan relatives) Opisthokonts UNICELLULAR, FLAGELLATED Nucleariids ANCESTOR Chytrids Other fungi  DNA evidence suggests that fungi are most closely related to unicellular nucleariids while animals are most closely related to unicellular choanoflagellates This suggests that fungi and animals evolved from a common flagellated unicellular ancestor and multicellularity arose separately in the two groups The oldest undisputed fossils of fungi are only about 460 million years old  50 µm Fossil fungal hyphae and spores from the Ordovician period (about 460 million years ago) (LM) The phylogenetic relationships between fungi and other eukaryotes are not well understood. A flagellated, aquatic, heterotrophic protist appears to be the common ancestor of both animals and fungi. Organisms of the fungal line developed into multicellular organisms with cell walls made of chitin. Figure 3. The hypothetical relations between the protists and the fungi. Animals and fungi probably evolved from aquatic flagellated protists. 3. Describe the key roles that fungi play in terms of nutrient recycling, ecological interactions and human impacts Fungi as Decomposers Fungi are efficient decomposers They perform essential recycling of chemical elements between the living and nonliving world  Fungi as Mutualists Fungi form mutualistic relationships with plants, algae, cyanobacteria, and animals All of these relationships have profound ecological effects Fungus-Plant Mutualisms Mycorrhizae are enormously important in natural ecosystems and agriculture Plants harbour harmless symbiotic endophytes that live inside leaves or other plant parts Endophytes make toxins that deter herbivores and defend against pathogens RESULTS Endophyte not present; pathogen present (E–P+) Both endophyte and pathogen present (E+P+) Leaf area damaged (%) 30 15 Leaf mortality (%) 20 10 10 5 0 0 E–P+ E+P+ E–P+ E+P+  Fungus-Animal Symbioses Some fungi share their digestive services with animals These fungi help break down plant material in the guts of cows and other grazing mammals  Lichens A lichen is a symbiotic association between a photosynthetic microorganism and a fungus in which millions of photosynthetic cells are held in a mass of fungal hyphae A fruticose (shrublike) lichen Crustose (encrusting) lichens A foliose (leaflike) lichen Variation in lichen growth forms  The fungal component of a lichen is most often an ascomycete Algae or cyanobacteria occupy an inner layer below the lichen surface The algae provide carbon compounds, cyanobacteria provide organic nitrogen, and fungi provide the environment for growth The fungi of lichens can reproduce sexually and asexually Asexual reproduction is by fragmentation or the formation of soredia, small clusters of hyphae with embedded algae  Lichens are important pioneers on new rock and soil surfaces Lichens are sensitive to pollution, and their death can be a warning that air quality is deteriorating  Fungi as Pathogens About 30% of known fungal species are parasites or pathogens, mostly on or in plants Some fungi that attack food crops are toxic to humans Animals are much less susceptible to parasitic fungi than are plants The general term for a fungal infection in animals is mycosis  Examples of fungal diseases of plants (a) Corn smut on corn (b) Tar spot fungus on (c) Ergots on rye maple leaves Penicillium, a mold commonly encountered as a decomposer of food 2.5 µm Like protists, the fungi can be grouped according to their ecological roles in the biosphere: MAJOR ROLE EXAMPLE ACTION DECOMPOSER common black bread mold breaks down organic material in bread mushrooms, morels , truffles mycelia break down organic material in soil PATHOGENS plant diseases: root rot, these fungi are specific for powdery mildew, Dutch elm particular plants and break disease down plant tissues animal diseases: athlete’s skin infections foot, vaginal infections psittacosis lung disease mold (Aspergillus) grows on grains, produces carcinogenic compounds (e.g. Aflatoxin) GROWTH PROMOTERS Mycorrhizae enhance uptake of minerals from the soil in 95% of vascular plants Distinguishing characteristics The fungi are eukaryotic and multicellular Fungi are non-motile and grow from the ends of somewhat linear bodies. Fungi have cell walls just like plant cells, however fungal cell walls are made of chitin whereas those of plant cells are made of cellulose.