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Bacteria BIO162 Fall 07 Page Baluch Domain Bacteria Differences (cell types, metabolism, etc) between microbes: Are results of evolution from a common ancestor Survival of the fittest for a specific environment Bergey’s Manual names ~ 5000 bacterial species (only 1% of existing bacteria!) Characteristics used in microbial classification include: Cell shape, staining reaction, motility, colony morphology, atmospheric & nutrients requirements, biochemical & metabolic activity, enzymes, pathogenicity, genetic material Three main phenotypic categories: Gram-negative Gram-positive Gram-variable (no cell wall) Morphology (cell shape) Three major shapes: Cocci (round) Bacilli (rod) spirilla (spiral or curved) 1 Morphology Grouping of cocci and bacilli Sometimes you can tell the shape of the bacteria from their names, but not always (Table 4-6) Cell shape Example Cocci Streptococcus pyogenes Staphylococcus aureus Neisseria gonorrhoeae Bacilli Bacillus anthracis Clostridium sp. Escherichia coli Salmonella sp. Mycobacterium sp. Pleomorphic Mycoplasma pneumonae 2 Staining procedures enable us to see and identify bacteria Simple stain – sufficient to determine cell shape and morphological arrangement e.g methylene blue Differential stain - differentiate bacteria based on composition of cell wall e.g Gramstain, Acid-fast stain Special stain Structural stain – color and isolate specific parts of bacteria e.g. capsule, flagella and endospores Types of dyes Acidic – used to stain basic (negatively charged) cell components Basic – used to stain acidic cell (positively charged) components Structural features of bacteria Nucleiod region & plasmids Cell Wall Glycocalyx (slime & capsule) Flagella Pili or Fimbriae Endospore 3 Bacterium have only about onethousandth as much DNA as a human Its chromosome is located in the nucleoid region Extrochromosomal DNA – plasmids Antibiotic resistance genes metabolism of unusual nutrients can be transferred between bacteria Bacterial Cell Wall Structure Gram stain differentiates bacteria into Gram-positive and Gram-negative groups. The two groups differ in the organization of the structures outside the plasma membrane but below the capsule (see Table 4-5) Mycobacterium species have special lipids in the cell wall and are often identified with acid-fast stain Gram stain 4 Comparison of Gram +ve & Gram –ve bacteria Gram +ve Gram -ve Gram stain reaction Blue to purple Pink to red Peptidoglycan layer in cell wall Thick Thin Teichoic acid in cell wall Present Absent Lipopolysaccharrides Absent (outer membrane) in cell wall Present Pathogenicity Less More deadly Antibiotic susceptibility More Less Many bacteria are motile Ability to “swim” using flagellum/flagella Some species can move at speeds exceeding 50 µm/sec, about 100 times their body length per second Most spiral-shaped or bacilli are motile; cocci are non-motile Capable of taxis (movement towards or away from stimuli) Many prokaryotes secrete another sticky protective layer Capsule (a.k.a slime layer, glycocalyx) glue together the cells that live as colonies Increase adherences to surface (e.g. teeth) biofilm May protect against host defense 5 More cell surface appendages Fimbriae allow pathogenic bacteria to stick to host mucus membrane Sex pili are used in conjugation between two bacteria (bacterial “sex”) Unique Bacteria: Rickettsia, Chlamydia & Mycoplasma Gram-negative bacteria Rickettsia Chlamydia Obligate intracellular pathogens (must live within a host) Transmitted by arthropods vectors Obligate intracellular pathogens Transmitted by direct contact Mycoplasma Smallest microbe Lack cell wall pleomorphic Resistant to certain antibiotics Unique bacteria: Photosynthetic bacteria Capable of using light as energy source Purple bacteria, green bacteria & cyanobacteria 6 Domain Archaea Prokaryotic cells Have different cell wall structure than bacteria Live in extreme environments Bacterial growth (p.200-2, 207-8) Growth in number of cells Multiply by binary fission As a bacterium grow to its optimal size (double cell constituents & genetic material), a new cell wall is synthesized in the middle cell divided into 2 halves Generation time (g) – time it takes for one cell to become two cells by binary fission (range from 20 min to 24 hr) If you inoculate a broth with 1 bacterium (g=30min). After 12 hours, as it divides, you’ll have 2 24 =16777216 bacteria! If you place 1 bacterium on an agar plate, 12 hr later, you have a mount of 16777216 cells colony www.cellsalive.com Bacterial (population) Growth Curve Lag phase – absorb nutrients & synthesize enzymes, genetic material; cell number DO NOT increase Log phase – cell number doubles; period of maximum division; generation time is determined from this phase Stationary phase – nutrients depleted; growth slows down and start dying; has the most population density Death phase – bacteria die at a rapid rate; some survive (may form spores) 7 Bacterial survival in nature is “Feast or Famine” mostly in stationary or death phase Endospore formation (sporulation) for some species (Bacillus sp. & Clostridium sp.) When nutrients become available, resume growth (germination) Endospores resistant to heat, cold, radiation, desiccation, and disinfectants 8