Lec #16 .pptx

PowerPoint® Lecture Presentations CHAPTER 23 Microbial Symbioses with Microbes, Plants, and Animals © 2018 Pearson Education, Inc. I. Symbioses between Microorganisms Figure 23.1 © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. 23.1 Lichens • L...

PowerPoint® Lecture Presentations CHAPTER 23 Microbial Symbioses with Microbes, Plants, and Animals © 2018 Pearson Education, Inc. I. Symbioses between Microorganisms Figure 23.1 © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. 23.1 Lichens • Lichens • leafy or encrusting microbial symbioses • often found growing on bare rocks, tree trunks, house roofs, and the surfaces of bare soils (Figure 23.1) • Lichens are a mutualistic relationship between a fungus and an alga (or cyanobacterium). • Alga is photosynthetic and produces organic matter; many are nitrogen-fixing as well. • The fungus provides a structure within which the phototrophic partner can grow protected from erosion and with dissolved inorganic nutrients. (Figure 23.2) • Lichens are more complex than previously considered as they contain bacterial and archaeal microbiota. © 2018 Pearson Education, Inc. II. Plants as Microbial Habitats • 23.3 The Legume–Root Nodule Symbiosis • 23.4 Mycorrhizae © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 23.7 © 2018 Pearson Education, Inc. 23.3 The Legume–Root Nodule Symbiosis • Infection of legume roots by nitrogen-fixing bacteria leads to the formation of root nodules that fix nitrogen. • leads to significant increases in combined nitrogen in soil • Nodulated legumes grow well in areas where other plants would not. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 23.8 23.3 The Legume–Root Nodule Symbiosis • Nitrogen-fixing bacteria need O2 to generate energy for N2 fixation, but the enzymes that fix nitrogen, the nitrogenases, are inactivated by O2. • In the nodule, free oxygen is bound up by O2binding protein leghemoglobin that serves as an “oxygen buffer” to protect nitrogenases from free oxygen. © 2018 Pearson Education, Inc. 23.3 The Legume–Root Nodule Symbiosis • In general, different rhizobia infect different species of legumes, so the bacteria that infect peas are different than those that infect clover. • Cross-inoculation group • group of related legumes that can be infected by a particular species of rhizobia © 2018 Pearson Education, Inc. 23.3 The Legume–Root Nodule Symbiosis • Critical steps in root nodule formation (Figure 23.10) • Step 1: Recognition and attachment of bacterium to root hairs (Figure 23.11) • Step 2: Excretion of Nod factors by the bacterium • Step 3: Bacterial invasion of the root hair • Step 4: Travel to the main root via the infection thread • Step 5: Formation of bacteroid state within plant cells • Step 6: Continued plant and bacterial division, forming the mature root nodule © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 23.10 23.4 Mycorrhizae • Mycorrhizae • mutualistic associations of plant roots and fungi • The fungus transfers inorganic nutrients from the soil to the plant, while the plant donates carbohydrates the fungus. © 2018 Pearson Education, Inc. to 23.4 Mycorrhizae • Ectomycorrhizae remain outside the plant roots. • Fungal cells form an extensive sheath around the outside of the root with only a little penetration into the root tissue. • found primarily in forest trees, particularly boreal and temperate forests © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 23.19 23.4 Mycorrhizae • Endomycorrhizae • Fungal mycelium becomes deeply embedded within the root tissue and is called arbuscular mycorrhizae. • more common than ectomycorrhizae • Found in >80 percent of terrestrial plant species, but cannot be cultured in pure culture. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 23.20 23.4 Mycorrhizae • Mycorrhizal fungi assist plants. • improve nutrient absorption • This is due to the greater surface area provided by the fungal mycelium. • help to promote plant growth © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Endophytic Insect Pathogenic Fungi © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. III. Insects as Microbial Habitats: Termites © 2018 Pearson Education, Inc. III. Insects as Microbial Habitats 23.7 Termites • Termites decompose cellulose and hemicellulose. • Termites classified as higher or lower based on phylogeny • Termite gut consists of foregut, midgut, and hindgut. • posterior alimentary tract of higher termites (Termitidae) • diverse community of anaerobes, including cellulolytic anaerobes capable of digesting cellulose © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. V. Mammalian Gut Systems as Microbial Habitats • The Rumen and Ruminant Animals © 2018 Pearson Education, Inc. 23.12 Alternative Mammalian Gut Systems • Microbial associations with certain animals led to an ability to catabolize plant fibers. • plant fibers composed of insoluble polysaccharides • cellulose most abundant component • Two digestive plans have evolved in herbivorous animals. (Figure 23.37) • foregut fermentation: fermentation chamber precedes the small intestine • hindgut fermentation: uses cecum and/or large intestine © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 23.37 23.13 The Rumen and Ruminant Animals • Microbes form intimate symbiotic relationships with higher organisms. • Ruminants • herbivorous mammals (e.g., cows, sheep, goats) • possess a special digestive organ (the rumen) • Cellulose and other plant polysaccharides are digested with the help of microbes. (Figure 23.38) • rumen well studied because of implanted sampling port © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 23.38 23.13 The Rumen and Ruminant Animals • The rumen contains 1010 to 1011 microbes per gram of rumen constituents. • Fermentation in the rumen is mediated by cellulolytic microbes that hydrolyze cellulose to free glucose that is then fermented, producing volatile fatty acids (e.g., acetic, propionic, butyric) and CH4 and CO2. (Figure 23.39) • Fatty acids pass through the rumen wall into the bloodstream and are utilized by the animal as its main energy source. © 2018 Pearson Education, Inc. © 2018 Pearson Education, Inc. Figure 23.39 © 2018 Pearson Education, Inc. 23.13 The Rumen and Ruminant Animals • Rumen microbes also synthesize amino acids and vitamins for their animal host. • Rumen microbes themselves can serve as a source of protein to their host when they are directly digested. • Anaerobic bacteria dominate in the rumen. • Rumen contains 300 to 400 bacterial “species.” (Figure 23.40) © 2018 Pearson Education, Inc. 23.13 The Rumen and Ruminant Animals • Abrupt changes in an animal's diet can result in changes in the rumen flora • Rumen acidification (acidosis) is one consequence of such a change. This can lead to inflammation of the rumen and potential acidification of the blood (which is potentially lethal for the cow). • Anaerobic protists and fungi are also abundant in the rumen. • Many of these eukaryotes perform metabolic reactions similar to those of their prokaryotic counterparts. • Rumen microorganisms often detoxify plant metabolites, which enables cattle to eat a more varied diet. (Figure 23.41) © 2018 Pearson Education, Inc.