microorganisms exam 3

• Anaerobic Chemotrophs


  • Atmosphere anoxic (no oxygen) for first 1.5 billion years that prokaryotes inhabited Earth
  • Early chemotrophs likely used anaerobic respiration
  • Terminal electron acceptors likely abundant CO2 or S
  • Others may have used fermentation
  • Today anaerobic habitats still present
  • Aerobes contribute by depleting O2
  • Mud, tightly packed soil limit diffusion of gases
  • Aquatic environments can become limiting
  • Human body (especially intestinal tract is anaerobic)
  • Anaerobic microenvironments in skin, oral cavity
• Anaerobic Chemolithotrophs


  • Chemolithotrophs oxidize inorganic chemicals for energy
  • Anaerobes use alternative electron acceptor
  • For example, CO2 or S
  • Others are aerobic using oxygen as the terminal electron acceptor
  • Relatively few discovered
  • Most in domain Archaea
  • Methanogens are one group
• Methanogens


  • Methanogens are group of methane-producing archaea
  • Oxidize H2 gas to generate ATP
  • Alternatives energy sources include formate, methanol, acetate
  • CO2 as terminal electron acceptor
  • Smaller energy yield than other electron acceptors
  • Sewage, swamps, marine sediments, rice paddies, digestive tracts where H2 and CO2 are available
  • Cows produce approximately 10 cubic feet/day of methane
• Anaerobic Chemoorganotrophs


  • Chemoorganotrophs oxidize organic compounds (for example glucose) to obtain energy
  • Anaerobes often use sulfur, sulfate as electron acceptor
  • Sulfur and Sulfate Reducing Bacteria
  • Produce hydrogen sulfide (rotten-egg smell)
  • H2S is corrosive to metals
  • Important in sulfur cycle
  • Some archaea
• Fermentation


  • Numerous anaerobic bacteria ferment ATP via substrate-level phosphorylation (glycolysis)
  • Many different organic energy sources, end products
  • The genera Clostridium and Clostridioides are common fermenters
• The Genera Clostridium and Clostridioides


  • Collectively referred to as clostridia
  • Gram-positive rods that can form endospores
  • Common soil inhabitants that live in the anaerobic microenvironments
  • Endospores tolerate O2, heat, drying, chemicals, and irradiation
  • Germinate and multiply when conditions become favorable
  • Pathogenic Clostridium include Tetanus (C. tetani), gas gangrene (C. perfringens), and botulism (C. botulinum)
  • Clostridioides difficile causes an antibiotic-associated diarrheal disease referred to as C. difficile infection (CDI)
  • Some are normal inhabitants of the intestinal tract of humans and other animals
• Lactic Acid Bacteria


  • Gram-positive bacteria that produce lactic acid as a product of fermentation
  • Most can grow in aerobic environments; lack catalase so they only ferment
  • Streptococcus inhabit oral cavity; normal microbiota
  • Some pathogenic (for example, β-hemolytic S. pyogenes)
  • S. thermophilus used to make yogurt
• Lactic Acid Bacteria


  • Lactococcus species used to make cheese
  • Enterococcus inhabit human, animal intestinal tract
  • Lactobacillus rod-shaped, common in mouth, vagina
  • Break down glycogen deposited in vaginal lining
  • Resulting low pH helps prevent vaginal infections
  • Important in production of fermented foods
• The Genus Propionibacterium


  • Produce propionic acid via fermentation
  • Can also ferment lactic acid
  • Can cause acne
  • Important in dairy industry: Swiss cheese
  • Typical nutty flavor
  • CO2 creates signature holes
• Anoxygenic Phototrophs


  • Likely the earliest photosynthesizers
  • Use hydrogen sulfide or organic compounds (not water) as reducing power for biosynthesis; do not generate oxygen
  • Modern-day phylogenetically diverse
  • Live in bogs, lakes, upper layers of mud
  • Little or no O2 but light penetrates
  • Different photosystems than plants, algae, cyanobacteria
  • Use unique bacteriochlorophyll; absorbs deep-penetrating blue wavelengths
• Purple Bacteria


  • Gram-negative; appear red, orange, or purple
  • Photosynthetic apparatus in cytoplasmic membrane
  • Purple Sulfur Bacteria may have gas vesicles to control depth
  • Most store sulfur in intracellular granules
  • Preferentially use H2S to generate reducing power
  • Other inorganic or organic (pyruvate) compounds
• Purple Non-Sulfur Bacteria


  • Moist soils, bogs, paddy fields
  • Preferentially use organic molecules instead of H2S as source of electrons
  • May store sulfur; granules outside cell
  • Remarkably diverse metabolism
  • Some use H2; Most can grow aerobically in absence of light using chemotrophic metabolism
• Green Bacteria


  • Gram-negative; typically, green or brownish
  • Green Sulfur Bacteria: Habitats similar to purple sulfur bacteria
  • Use H2S; form sulfur granules outside of cell
  • Accessory pigments located in chlorosomes
  • May have gas vesicles
  • Strict anaerobes
• Oxygenic Phototrophs


  • Cyanobacteria
  • Earliest oxygenic phototrophs
  • Introduction of O2 began approximately 3 billion years ago
  • Use water as source of electrons for reducing power
  • Still play essential role as primary producers
  • Harvest sunlight to convert CO2 into organic compounds
  • Initially thought to be algae, called blue-green algae
  • Diverse group of Gram-negative bacteria
  • Many convert N2 to ammonia: nitrogen fixation
• Cyanobacteria


  • Morphologically diverse
  • Unicellular: cocci, rods, spirals
  • Multicellular: filamentous associations: trichomes (hair-like)
  • May be in sheath
  • Motile trichomes glide as unit
  • Those that live in aquatic environment have gas vesicles for vertical movement in water
• Cyanobacteria


  • Large numbers can accumulate in freshwater habitats
  • Called a bloom
  • Sunny, hot weather can lyse cells, create scum
  • Photosystems (I and II) like those in chloroplasts of algae, plants, which evolved from ancestral cyanobacteria
• Nitrogen Fixing Cyanobacteria


  • Critical important ecologically
  • Incorporate N2 into organic material that is used by other organisms
  • Nitrogenase destroyed by O2 must be protected
  • Anabaena form specialized heterocysts
  • Lack photosystem II
  • A. azollae fixes N2 in special sac of fern
  • Synechococcus fix N2
• Aerobic Chemolithotrophs


  • Aerobic chemolithotrophs gain energy by oxidizing reduced inorganic chemicals
  • Sulfur-oxidizing bacteria: Gram-negative rods
  • Energy from oxidation of sulfur, sulfur compounds including S2O3 is terminal electron acceptor; generates sulfuric acid
  • Important in sulfur cycle
  • Unicellular forms can affect environmental pH
• Nitrifiers


  • Nitrifiers are a diverse group of Gram-negatives
  • Oxidize inorganic nitrogen compounds for energy
  • Concern to farmers using ammonium fertilizer
  • Can deplete water of O2 if wastes high in ammonium
  • Two groups; usually grow in close association
  • Ammonium oxidizers
  • Nitrite oxidizers
• Hydrogen-Oxidizing Bacteria


  • Aquifex, Hydrogenobactera among few hydrogen-oxidizing bacteria that are obligate chemolithotrophs
  • Thermophilic; typically live in hot springs
  • Some Aquifex have maximum growth at 95 0C
  • Based on 16S rRNA, believed one of earliest bacterial forms to exist on Earth
  • O2 requirements low
• Aerobic Chemoorganotrophs


  • Oxidize organic compounds for energy
  • Use O2 as terminal electron acceptor
  • Some inhabit specific environments, others ubiquitous
• Obligate Aerobes


  • Cannot ferment
  • Micrococcus: Gram-positive cocci
  • Found in soil, dust particles, inanimate objects, skin, mouth
  • Pigmented colonies – waxy lipids
  • Tolerate dry, salty conditions
• Irish Potato Famine


  1846 to 1850
• Water mold (oomycete)


  Phytophthora infestans
• Phytophthora infestans ruined the potato crop
• Estimated 1.5 million people died (1 in 8 people) during the famine; more than 1 million moved; Ireland's population fell by 25%
• The Genus Mycobacterium


  • Acid-fast bacteria (resistant to de-colorization by acid/alcohol)
  • Mycolic acid in cell wall prevents Gram-staining; acid-fast staining used
  • Generally pleomorphic rods
  • Many saprophytes, living on dead and decaying matter
  • Notable pathogens: M. tuberculosis, M. leprae
  • More resistant to disinfectants, often resistant to antimicrobial drugs
• Easy to grow, nearly complete food source that could be stored for months led to dependence on single food source
• The Genus Pseudomonas


  • Gram-negative rods; polar flagella; often produce pigments
  • Most are strict aerobes; no fermentation
  • Widespread: soil, water
  • Most harmless
  • Some pathogens: P. aeruginosa common opportunistic pathogen
• In 2009, genomes of potato and Phytophthora infestans were sequenced
• Potato blight results in nearly $10 billion/year in loss
• Microscopic Eukaryotes


  Informal groups of microscopic eukaryotes
• Microscopic Eukaryotes


  • Algae
  • Fungi
  • Protozoa
• The Genera Thermus and Deinococcus


  • Related genera with unusual cell walls
  • Thermus are thermophilic, valuable for their heat-stable enzymes
  • Stain Gram-negative
  • Deinococcus are extraordinarily radiation resistant
  • Dose shatters genome into many fragments, yet enzymes repair damage
  • Scientists hope to genetically engineer species to help clean up radioactive wastes
  • Stain Gram-positive
• Eukaryotes


  • Nucleus; membrane-bound organelles; no peptidoglycan; usually well-developed cytoskeleton
  • May be haploid and/or diploid; complex life cycles
  • Asexual reproduction via mitosis
  • Sexual reproduction via meiosis
  • Diploid cells produce haploid cells
  • Fusion of two gametes forms diploid cell; recombination of genetic material
• Facultative Anaerobes


  • Use aerobic respiration, but can ferment if O2 is not available
  • Corynebacterium: Gram-positive pleomorphic rods
  • Often club-shaped and form V shapes
  • Referred to as coryneforms or diphtheroids
  • Generally facultative anaerobes; some strict aerobes
  • Many harmless in normal microbiota
  • C. diphtheriae causes diphtheria
• Fungi


  Molds, yeasts, mushrooms
• Mycology


  Study of fungi
• Fungal forms


  • Yeasts
  • Molds
  • Mushrooms
• Heterotrophs


  Main decomposers of organic materials (for example lignin and cellulose)