1/21/2017. Lecture 5: Chapters 26 & 27 Diversity of Prokaryotes & Protists

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1 Lecture 5: Chapters 26 & 27 Diversity of Prokaryotes & Protists Prokaryotes Two domains Bacteria Archaea While these are different domains, we will first consider the groups together as they are similar in basic structure Found almost everywhere, in most environments Shapes Spheres (cocci) Rods (bacilli) Spirals (spirochetes) Size Much smaller than eukaryotes -5μm vs 0-00μm Cell surface Cell wall that provides protection, maintains cell shape, prevents cell from bursting in a hypotonic solution Fig Cell surface Cell walls in bacteria contain peptidoglycan (network of sugar polymers crosslinked by short proteins) Cell walls in archaea lack peptidoglycan and phospholipids contain isoprene Cell surface Use Gram stain technique to divide bacteria into groups Gram positive have simple walls with a large amount of peptidoglycan, Gram negative have less/no peptidoglycan and often much more complex structures with outer membrane Structural and Functional Adaptations Cell surface Cell wall may be covered with a capsule (sticky layer) for attachment to surfaces Fimbriae and pilli are hairlike extensions of the cell surface, also play a role in attachment to surfaces

2 Cell surface Flagella help cells to move usually have more than one Internal and genomic Membrane specialization No membrane bound organelles, but sometimes specialized membranes that perform metabolic functions Oxygen Revolution For the first 2.3 billion years of Earth s existence, no oxygen in atmosphere Once photosynthesis evolved in complex bacteria, oxygen started to accumulate Cyanobacteria became numerous around bya Internal and genomic Genome Single, circular chromosome in nucleoid region Often find plasmids, small circular pieces of DNA consisting of only a few genes Reproductive Reproduce by binary fission (splitting of cells) Exchange genes through conjugation Produce endospores resistant cells formed during stress Structure surrounded by tough wall, resistant to desiccation, heat, cold, etc. Prokaryotic Metabolic Diversity Autotrophs: synthesize their own complex organic molecules (Table 26.2) Photoautotrophs photosynthetic, capture energy from sunlight to synthesize organic compounds from CO 2 Chemoorganoautotrophs oxidize organic molecules with high potential energy (e.g. sugars) for ATP production Chemolithoautotrophs oxidize inorganic molecules with high potential energy (e.g. ammonia or methane); ATP produced by cellular respiration, and inorganic molecules serve as electron donor; rock-feeders ; synthesize own organic molecules Heterotrophs: source of carbon is organic molecules (Table 26.2) Photoheterotrophs use light for energy, but consume organic molecules to obtain carbon Chemoorganoheterotrophs consume organic molecules for energy and carbon Chemolithotrophic heterotrophs oxidize inorganic molecules with high potential energy (e.g. ammonia or methane); ATP produced by cellular respiration, and inorganic molecules serve as electron donor; rock-feeders ; do not synthesize own organic molecules Prokaryotic Metabolic Modes Obligate aerobes require O 2 for cellular respiration Facultative anaerobes use O 2 if present, but can also grow by fermentation Obligate anaerobes poisoned by O 2 2

3 Some use fermentation Some use anaerobic respiration which replaces O 2 with other substances such as nitrate or sulfate ions in the electron transport chain Other Metabolic Adaptations Nitrogen metabolism Nitrogen fixation conversion of atmospheric nitrogen to ammonia which can be used to build organic molecules Metabolic cooperation Cooperation among prokaryotes allowing them to utilize environmental resources not otherwise available Biofilms colonies of cells where some secrete adherence proteins, some secrete substances to recruit additional cells Prokaryote Phylogeny Molecular Systematics Older phylogenies used physical and metabolic traits to determine relatedness Unfortunately, prokaryotes evolve quickly and many traits are likely convergences Molecular studies are much more useful and provide better resolution Clearly establish domain divisions between Archaea and Bacteria, and further resolve lower evolutionary relationships Bacteria versus Archaea Bacteria generally divided into groups by molecular and physical characteristics Firmicutes, Spirochaetes, Actinobacteria, Chlamydiae, Cyanobacteria, and Proteobacteria Review charts on pages Be familiar with names and the distinguishing characteristics of the groups above (especially metabolic diversity and human & ecological impacts) Firmicutes: Mostly rod and spherical Metabolic diversity: nitrogen-fixers, non-oxygenic photosynthesis, fermentation, etc. Many live in human gut; others cause diseases such as anthrax, botulism, tetanus, and strep throat Lactic acid producers used to ferment milk for cheese and yogurt Spirochaetes Small number of species Corkscrew shape Most are fermenters Cause diseases such as syphilis and Lyme disease Actinobacteria Varied shape, from rods to filaments Mostly heterotrophic, including some parasites Many antibiotics have been isolated from these species Some cause diseases such as tuberculosis and leprosy 3

4 Chlamydiae Small number of species (3) Spherical shape and small All parasites inside host cells Infections can cause blindness and STD of urogenital tract Cyanobacteria Independent cells, chains forming filaments, or colonies All photosynthetic Many also fix nitrogen Responsible for initial rise of oxygen in atmosphere Some live with fungi to form lichens Proteobacteria Large diversity of morphology and metabolism Rods, spheres, spirals; some have stalks; some motile; some form colonies Nearly all metabolic pathways known to bacteria (except oxygenic photosynthesis Examples: E. coli, species that cause Legionnaire s disease, cholera, gonorrhea, and others Bacteria versus Archaea Archaea the extremophiles (love extreme environments Extreme thermophiles live in very hot environments such as volcanic springs and deep-sea hydrothermal vents Extreme halophiles live in highly saline environments like Great Salt Lake Methanogens poisoned by O 2, obtain energy from CO 2 and release methane as waste product Produce methane commonly called swamp gas or marsh gas Ecological Roles Prokaryotes are important as decomposers Break down dead materials and wastes, and recycle chemicals between living and nonliving environments Bioremediation use of organisms (usually bacteria) to remove pollutants from soil, air, or water Can fertilize contaminated sites to encourage growth of existing bacteria and archaea that can break down the toxic compounds Ecological Roles Prokaryotes convert organic and inorganic compounds to materials that can be used by other organisms Nitrogen fixation and plants Chemoautotrophic based food chains Mutualism in digestion 4

5 Synthesize nutrients in large intestine of many animals, including humans Digest cellulose from plant material in ruminant animals (like cows and deer) Prokaryotic Pathogens It s a constant battle for humans! Account for about half of all human diseases TB, Cholera, Lyme disease, Food poisoning They are the whole reason we have antibiotics Usually disease is a result of poisons released by prokaryotes Exotoxins proteins secreted by prokaryotes Endotoxins Components of the outer membrane of Gram-negative bacteria released when bacterial cells die On to Protists The Protists - Overview This is not a true evolutionary unit, simply a collective term for any eukaryote not a plant, animal, or fungus the systematics are in constant transition Some protists are more closely related to plants/animals/fungus than to other protists Most are single-celled, some are colonies, and a few are multicellular The Protists - Overview Diverse modes of nutrition - photosynthetic, ingestive feeding, and absorptive feeding Mixotrophs: combine photosynthesis and heterotrophic nutrition Three categories (but definitely not monophyletic groups) Photosynthetic protists referred to as algae Non-photosynthetic, animal-like are the protozoa Fungus-like, absorptive protists (no general name) May be decomposers or parasites Origins of Protist Diversity Considerable evidence to support an endosymbiosis pathway A process in which unicellular organisms engulf other cells which become endosymbionts and later, organelles in a host cell In early eukaryotes, this was likely a photosynthetic cyanobacterium Secondary endosymbiosis red or green algae become endosymbionts themselves Gave rise to chloroplasts with more than 2 membranes Amoebozoa Plasmodial Slime Molds Huge supercells form with many nuclei Decomposers Form spores when food scarce 2. Excavata Diplomonads,Parabasalids, and Euglenids Common characteristics 5

6 Lack mitochondria Did they evolve from eukaryotes that evolved before mitochondria? Likely not: they have genes of mitochondrial origin, or unusual organelles that appear to be vestigial mitochondria Excavated feeding groove on one side of cell Often parasitic (Giardia, Trichomonas) Diplomonads and Parabasalids Diplomonads include Giardia intestinalis An intestinal parasite contracted from cysts in feces contaminated water Parabasalids include Trichomonas vaginalis A common inhabitant of vagina in humans May become pathogenic in combination with bacterial gene that allows protist to feed on epithelial cells, and can become STD occurring in male urethra Euglenids Some have chloroplasts; most ingest bacteria and other small cells Reproduce only asexually 3. Plantae A monophyletic group including glaucophyte algae, red algae, green algae, and land plants Red Algae: Mostly marine habitats Red color due to accessory pigment phycoerythrin Some unicellular, most multicellular (filamentous or crust-like) Nearly all photosynthetic, but some parasitic Rhizaria Single-celled amoebae No cell walls, but some have shell-like coverings Amoeboid movement via slender pseudopodia Most abundant: Foraminiferans Shells with holes Capture bacteria or other cells with pseudopodia Alveolata Characterized by membrane bound sacs (alveoli) just under the plasma membrane Function of alveoli unknown maybe ion balance? All unicellular Three groups Ciliates, Dinoflagellates, and Apicomplexans Ciliata Large group named for use of cilia to move and feed Characteristics: 6

7 Two types of nuclei (polyploid macronuclei and diploid micronuclei) Complex reproduction involving binary fission and conjugation (exchange of genetic material) Example: Paramecium Dinoflagellata Thousands of species Abundant component of marine and freshwater phytoplankton, but a few are heterotrophic Unicellular to colonial Example: Dinoflagellate blooms (population explosion) causes red tide Toxic byproducts kill invertebrates and fish, poison humans Apicomplexa Parasites of animals Have system of organelles at one end, called apical complex Used to penetrate host Lack cilia or flagella, but move by amoeboid movement Famous example is Plasmodium Causes malaria Develop in the liver Reproduce in RBCs Rupture of blood cells causes recurrent fever characteristic of malaria Results in 2mil deaths each year, especially in the tropics 6. Stramenopiles Include heterotrophs and some algae Characteristics Possess flagellum with many fine, hairlike projections (heterokonts) Often hairy flagellum is paired with smooth flagellum Oomycota (the water molds) Originally thought to be fungi, but have cell walls of cellulose (in fungi cell walls are chitin) Molecular analyses supports this distinction Most are decomposers in freshwater ecosystems Some are parasites on plants in terrestrial ecosystem Cause severe crop damage in grapes, potatoes, etc. Diatoms Highly diverse, unicellular algae Some form chains Unique, protective, box-like shells of silica Photosynthetic Major component of the phytoplankton (base of marine food webs) 7

8 Phaeophyta (Brown Algae) These are the largest and most complex algae Most are called seaweeds All are multicellular Most are marine Derive color from carotenoids in plastids Brown Algae cont. Many have specialized tissues and organs Thallus a plant-like, seaweed body Holdfast rootlike structure to anchor the alga Stipe stemlike structure that supports leaflike blades (site of most photosynthesis) Brown Algae Important to humans!!! Most are harvested for food Gel-forming substances from cell walls used to thicken processed foods like ice cream, pudding, and even toothpaste Algin Agar Carrageenan All for today 8