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Characterizing and Classifying Prokaryotes

Characterizing and Classifying Prokaryotes. 11. General Characteristics of Prokaryotic Organisms. Prokaryotes Most numerous and diverse group of cellular microbes Thrive in various habitats Only a few are capable of colonizing humans and causing disease.

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Characterizing and Classifying Prokaryotes

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  1. Characterizing and Classifying Prokaryotes 11

  2. General Characteristics of Prokaryotic Organisms • Prokaryotes • Most numerous and diverse group of cellular microbes • Thrive in various habitats • Only a few are capable of colonizing humans and causing disease

  3. Figure 11.1 Typical prokaryotic morphologies.

  4. General Characteristics of Prokaryotic Organisms • Endospores • Produced by Gram-positive bacteria Bacillus and Clostridium • Each vegetative cell transforms into one endospore • Each endospore germinates to form one vegetative cell • Defensive strategy against unfavorable conditions • Endospores are often difficult to kill • Concern to food processors, health care professionals, and governments

  5. Figure 11.2 Locations of endospores. Endospore Endospore Vegetative cell

  6. General Characteristics of Prokaryotic Organisms • Reproduction of Prokaryotic Cells • All reproduce asexually • Several different methods • Binary fission (most common) • Snapping division • Reproductive spores • Budding • Viviparity

  7. Bacterial Growth: Overview

  8. Figure 11.3 Binary fission. Cell wall Cell replicates its DNA. 1 Cytoplasmic membrane Nucleoid Replicated DNA 2 The cytoplasmic membrane elongates, separating DNA molecules. Cross wall forms; membrane invaginates. 3 4 Cross wall forms completely. Daughter cells may separate. 5

  9. Figure 11.4 Snapping division, a variation of binary fission. Newer, inner portion of cell wall Older, outer portion of cell wall Ruptured remains of old cell wall Hinge

  10. Figure 11.5 Spores of actinomycetes. Filamentous vegetative cells Spores

  11. Figure 11.6 Budding.

  12. General Characteristics of Prokaryotic Organisms • Reproduction of Prokaryotic Cells • Epulopiscium and its relatives have unique method of reproduction • Live offspring emerge from the body of the dead mother cell (viviparity) • First noted case of viviparous behavior in prokaryotic world

  13. Figure 11.7 Viviparity in Epulopiscium.

  14. General Characteristics of Prokaryotic Organisms • Arrangements of Prokaryotic Cells • Result from two aspects of division during binary fission • Planes in which cells divide • Separation of daughter cells

  15. Figure 11.8 Arrangements of cocci. Plane of division Diplococci Streptococci Tetrads Sarcinae Staphylococci

  16. Figure 11.9 Arrangements of bacilli. Single bacillus Diplobacilli Streptobacilli Palisade V-shape

  17. General Characteristics of Prokaryotic Organisms • Tell Me Why • Why does binary fission produce chains of cocci in some species but clusters of cocci in other species?

  18. Modern Prokaryotic Classification • Currently based on genetic relatedness of rRNA sequences • Three domains • Archaea • Bacteria • Eukarya • Bergey's Manual of Systematic Bacteriology provides prokaryotic classification scheme

  19. Figure 11.10 Prokaryotic taxonomy. Thermophilic bacteria PHYLUM DEINOCOCCUS-THERMUS PHYLUM CHLOROFLEXI (green nonsulfur) Deeply branching bacteria PHYLUM EURYARCHAEOTA Methanogens PHYLUM AQUIFICAE Nitrifying (β) BACTERIA PHYLUM CYANOBACTERIA Halophiles ARCHAEA GRAM-NEGATIVE BACTERIA Myxobacteria (δ) Purple nonsulfur (α) PHYLUM PROTEOBACTERIA PHYLUM CRENARCHAEOTA Campylobacteria (ε) Nitrogen fixing (α) Rickettsias (α) Gammaproteobacteria (γ) PHYLUM FUSOBACTERIA PHYLUM CHLOROBI (green sulfur) Selenomonas Streptomyces Thermophilic archaea Atopobium TIME PHYLUM BACTEROIDETES Neisserias (β) Corynebacterium Mycobacterium Nocardia PHYLUM PLANCTOMYCETES Arthrobacter PHYLUM FIBROBACTERES Low G+C Gram-positive PHYLUM FIRMICUTES Clostridia Mycoplasmas Bacilli, lactobacili, cocci PHYLUM SPIROCHAETES PHYLUM CHLAMYDIAE PHYLUM ACTINOBACTERIA High G+C Gram-positive GRAM-POSITIVE BACTERIA

  20. Modern Prokaryotic Classification • Tell Me Why • Why are taxonomic names and categories in our current taxonomic scheme different from those in 1990?

  21. Survey of Archaea • Common features • Lack true peptidoglycan • Cell membrane lipids have branched hydrocarbon chains • AUG codon codes for methionine • Two phyla: Crenarchaeota, Euryarchaeota • Reproduce by binary fission, budding, or fragmentation • Are cocci, bacilli, spirals, or pleomorphic • Not known to cause disease

  22. Figure 11.11 Archaea.

  23. Survey of Archaea • Extremophiles • Require extreme conditions to survive • Temperature, pH, and/or salinity • Prominent members are thermophiles and halophiles

  24. Survey of Archaea • Extremophiles • Thermophiles • DNA, RNA, cytoplasmic membranes, and proteins do not function properly below 45ºC • Hyperthermophiles – require temperatures over 80ºC • Two representative genera • Geogemma • Pyrodictium

  25. Figure 11.12 Some hyperthermophilic archaea live in hot springs.

  26. Survey of Archaea • Extremophiles • Thermophiles • Thermophilic enzymes are used for research and industrial applications • Recombinant DNA technologies • Additives in laundry detergents

  27. Survey of Archaea • Extremophiles • Halophiles • Inhabit extremely saline habitats • Depend on greater than 9% NaCl to maintain integrity of cell walls • Many contain red or orange pigments • May protect from sunlight • Most studied – Halobacterium salinarium

  28. Figure 11.13 The habitat of halophiles: highly saline water.

  29. Survey of Archaea • Extremophiles • Halophiles • Halobacterium salinarium • Most studied halophile • Photoheterotroph • Lacks photosynthetic pigments • Uses bacteriorhodopsins to establish proton gradient

  30. Survey of Archaea • Methanogens • Largest group of archaea • Convert carbon dioxide, hydrogen gas, and organic acids to methane gas • Convert organic wastes in pond, lake, and ocean sediments to methane • Some live in colons of animals • One of primary sources of environmental methane • Produced ~10 trillion tons of methane buried on ocean floor • Digest sludge during sewage treatment

  31. Survey of Archaea • Tell Me Why • Why did scientists formerly think archaea were a type of bacteria?

  32. Survey of Bacteria • Deeply Branching and Phototrophic Bacteria • Deeply branching bacteria • Scientists believe these organisms are similar to earliest bacteria • Autotrophic • Live in habitats similar to those thought to exist on early Earth • Aquifex • Considered to represent earliest branch of bacteria • Deinococcus • Has outer membrane similar to Gram-negatives but stains Gram-positive

  33. Survey of Bacteria • Deeply Branching and Phototrophic Bacteria • Phototrophic bacteria • Phototrophs that contain photosynthetic lamellae • Autotrophic • Divided into five groups based on pigments and source of electrons for photosynthesis • Blue-green bacteria (cyanobacteria) • Green sulfur bacteria • Green nonsulfur bacteria • Purple sulfur bacteria • Purple nonsulfur bacteria

  34. Figure 11.14 Examples of cyanobacteria with different growth habits. Vegetative cell Heterocyst Akinete Sheath (glycocalyx)

  35. Figure 11.15 Deposits of sulfur within purple sulfur bacteria.

  36. Photosynthesis: Comparing Prokaryotes and Eukaryotes

  37. Survey of Bacteria • Low G + C Gram-Positive Bacteria • G + C content below 50% • Have similar 16S rRNA sequences • Classified in phylum Firmicutes • Rod-shaped, obligate anaerobes

  38. Survey of Bacteria • Low G + C Gram-Positive Bacteria • Clostridia • Rod-shaped, obligate anaerobes • Important in medicine and industry • Produce toxins that cause diseases in humans • Endospores survive harsh conditions • Related microbes include Epulopiscium, sulfate-reducing microbes, and Selenomonas

  39. Survey of Bacteria • Low G + C Gram-Positive Bacteria • Mycoplasmas • Facultative or obligate anaerobes • Lack cell walls • Smallest free-living cells • Colonize mucous membranes of the respiratory and urinary tracts of animals

  40. Figure 11.16 The distinctive "fried egg" appearance of Mycoplasma colonies.

  41. Survey of Bacteria • Low G + C Gram-Positive Bacteria • Other low G + C bacilli and cocci • Bacillus • Endospore-forming aerobes and facultative anaerobes • Many common in soil • Bacillus thuringiensis toxin is used by farmers and gardeners as an insecticide • Bacillus anthracis causes anthrax • Other species synthesize antibiotics

  42. Figure 11.17 Crystals of Bt toxin, produced by the endospore-forming Bacillus thuringiensis. Bt toxin Bacillus thuringiensis

  43. Survey of Bacteria • Low G + C Gram-Positive Bacteria • Other low G + C bacilli and cocci • Listeria • Contaminates milk and meat products • Capable of reproducing under refrigeration • Survives inside phagocytic white blood cells • Rarely causes disease in adults • In pregnant women, can kill the fetus if crosses the placenta

  44. Survey of Bacteria • Low G + C Gram-Positive Bacteria • Other low G + C bacilli and cocci • Lactobacillus • Grows in the human mouth, stomach, intestinal tract, and vagina • Rarely causes disease • Inhibits the growth of pathogens within the body • Used in the production of various foods

  45. Survey of Bacteria • Low G + C Gram-Positive Bacteria • Other low G + C bacilli and cocci • Streptococcus and Enterococcus • Cause numerous diseases • Various strains of multi-drug-resistant streptococci • Staphylococcus • One of the most common inhabitants of humans • Produces toxins and enzymes that contribute to disease

  46. Survey of Bacteria • High G + C Gram-Positive Bacteria • Corynebacterium • Pleomorphic aerobes and facultative anaerobes • Produces metachromatic granules • Mycobacterium • Aerobic rods that sometimes form filaments • Slow growth, partly due to mycolic acid in its cell walls • Some species are pathogens of animals and humans

  47. Survey of Bacteria • High G + C Gram-Positive Bacteria • Actinomycetes • Form branching filaments resembling fungi • Cause disease primarily in immunocompromised patients • Important genera include Actinomyces, Nocardia, Streptomyces

  48. Figure 11.18 The branching filaments of actinomycetes. Spores

  49. Survey of Bacteria • High G + C Gram-Positive Bacteria • Actinomycetes • Actinomyces • Normally present in oral cavity and throats of humans • Nocardia • Soil- and water-dwelling aerobes • Can degrade a variety of pollutants • Streptomyces • Recycles nutrients in the soil • Produces most of the important antibiotics

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