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Bacterial Form and Function • Microbiology- Ch. 4 pp 87-101 Structure of a Prokaryotic Cell Prokaryote Structures: 1. Appendages- flagella, pili, fimbrae 2. Cell envelope- glycocalyx, cell wall , cell membrane 3. Cytoplasm- ribosomes, granules, nucleoid/chromosome. Bacterial Appendages: • Pili (pl), pilus (s) – Only found in gram negative bacteria – hollow, hairlike structures of protein larger and more sparse than fimbriae. – allow bacteria to attach to other cells. – sex pilus, - transfer from one bacterial cell to another- conjugation. • fimbriae (pl) fimbria (s) – Adhesion to cells and surfaces – Responsible for biofilms. – Pathogenesis of gonococcus and E.coli • Flagella (pl), flagellum(s) – Motility– long appendages which rotate by means of a "motor" located just under the cytoplasmic membrane. – Bacteria may have one, a few, or many flagella in different positions on the cell. – All spirilla, half of bacilli, rare cocci – Advantages- chemotaxis-positive and negative. Motility• Flagella vary in number and arrangement. • Polar arrangment– Monotrichious- 1 flagellum at one end • Fastest; Pseudomonas -example – Lophotrichious- tuft at one end – Amphitrichious- bipolar • Peritrichious– Multiple flagella; randomly dispersed around the bacterial cell – E.coli -example Structure of flagella allows for 360 degree filament rotation Flagellar arrangements Detection of Motility 1. Stab line in semisolid motility agar growth out from the streak line indicates motility. A= motile; B=nonmotile 2. Motility plate 3. Hanging drop- from actively growing culture 18-24 hrs old. directional movement vs. “brownian movement Bacterial Surface Structure- cell envelope Bacteria have some or all of the following structures: 1. Glycocalyx- capsule or slime layer – – – – – layer of polysaccharide (sometimes proteins) Different composition in certain bacteria• Streptococcus pneumoniae- capsule- tighter • Slime layer- looser, washes off protects the bacterial cell from phagocytosis associated with pathogenic bacteria -Staphylococcus aureus. Glycocalyx- colonize nonliving materials- plastics, catheters, medical devices. 1. Cell wall – • • peptidoglycan (polysaccharides + protein), Support and shape of a bacterial cell. The three primary shapes in bacteria are: » coccus (spherical), » bacillus (rod-shaped) » spirillum (spiral). » Mycoplasma are bacteria that have no cell wall and therefore have no definite shape. 2. Cell wall – peptidoglycan (polysaccharides + protein) Repeating glycan chains (N acetyl glucosamine and N acetyl muramic acid) with crosslinked peptides. Support and shape of a bacterial cell. The three primary shapes in bacteria are: » coccus (spherical), » bacillus (rod-shaped) » spirillum (spiral). » Mycoplasma are bacteria that have no cell wall and therefore have no definite shape. Differences in Cell Wall Structure • Basis of Gram Stain Reaction – Hans Christian Gram- 1884 • Differential Stain • Gram Positive vs Gram Negative Cells • Gram Positive Cells– Thick peptidoglycan layer with embedded teichoic acids • Gram Negative Cells– Thin peptidoglycan layer, outer membrane of lipopolysaccharide. Gram Stain Reaction • Hans Christian Gram- 1880s • Divides bacteria into 2 main groups– Gram positive – Gram negative • Also- gram variable • Gram nonreactive • Gram positive bacteria – many layers of peptidoglycan and teichoic acids. – Form a crystal violet-iodine-teichoic acid complex • Large complex,difficult to decolorize • Gram negative cells – – – – Very thin peptidoglycan No teichoic acids Alcohol decolorizer readily removes the crystal violet. Alcohol also dissolves the lipopolysaccharide of the cell wall. • Gram variable cells – Some cells retain crystal violet; some decolorize and take up the safranin – 4 factors• • • • Genetics- variable amount of teichoic acid. Age of culture- older cultures have variable amount of teichoic acid Growth medium- necessary nutrients not available Technique– smear not thin or evenly made. – Staining procedure not done correctly- decolorizer left on too long. • Gram nonreactive cells – Have peptidoglycan but have very waxy- thick lipids –waterproof, dyes cannot enter either. – Examples- Mycobacterium- tuberculosis and leprosy. • Alternative staining- acid fast stain- Cell wall deficient forms Figure 4.17 • L- forms ( Lister Institute where discovered) – Bacteria loses cell wall during the life cycle • Result of a mutation in cell wall forming genes • Induced by treating with lysozyme or penicillin which disrupts the cell wall – Protoplast• G + bacterium with no c. wall, only a c. membrane • Fragile, easily lysed – Spheroplast• G – bacterium loses peptidoglycan, but has outer membrane • Less fragile but weakened. Surface structures continued: • Outer membrane – This lipid bilayer is found in Gram negative bacteria and is the source of lipopolysaccharide (LPS) in these bacteria – LPS is toxic and turns on the immune system. – Not found in Gram positive bacteria. Cell membrane • Located just beneath cell wall • Very thin • Lipid bilayer, similar to the plasma membrane of other cells. Transport of ions, nutrients and waste across the membrane • Typical – 30-40% phospholipids – 60-70% proteins • Exceptions– Mycoplasma- sterols – Archaea- unique branched hydrocarbons Mesosome Extension of cell membrane – Folding into cytoplasm – internal pouch – Increases surface area. • Gram-positive bacteria-prominent • Gram negative bacteria- smaller,harder to see. • Functions– Cell wall synthesis – Guides duplicated chromosomes into the daughter cells in cell division. Photosynthetic Prokaryotes • Cyannobacterium- dense stacks of internal membranes with photosynthetic pigments. Functions of Cell Membrane • Carries out functions normally carried out by eukaryote organelles. • Site for energy functions • Nutrient processing • Synthesis • Transport of nutrients and waste • Selectively permeable • Most enzymes of respiration and ATP synthesis • Enzyme synthesis of structural macromolecules – Cell envelope and appendages • Secretion of toxins and enzymes into environment. Cell cytoplasm • Encased by cell membrane • Dense, gelatinous • Prominent site for biochemical and synthetic activities • 70-80% water- solvent • Mixture of nutrients- sugar, amino acids, salts – Building blacks for cell synthesis and energy Bacterial chromosome • Singular circular strand of DNA • Aggregated in a dense area- nucleiod • Long molecule of DNA tightly coiled around protein molecules. • Plasmids– Nonessential pieces of DNA • Often confer protection- resistance to drugs – – – – Tiny, circular Free or integrated Duplicate and are passed on to offspring Used in genetic engineering Ribosomes • Site of protein synthesis • Thousands – Occurs in chains –polysomes • 70S – 2 smaller subunits – 30S and 50S Inclusions • If nutrients abundant- stored intracellularly • Granules– Crystals of inorganic compounds not enclosed by membranes • Sulfur granules- photosynthetic • Polyphosphate- corynebacterium • Metachromatic- Mycobacterium Bacterial Internal Structures • Endospores – inert, resting, cells produced by some G+ genera: Clostridium, Bacillus and Sporosarcina • have a 2-phase life cycle: – vegetative cell – metabolically active and growing – endospore – when exposed to adverse environmental conditions; capable of high resistance and very long-term survival » Features of spores- size, shape, location=identification – sporulation -formation of endospores • • • • hardiest of all life forms Forms inside a cell- functions in survival not a means of reproduction withstands extremes in heat, drying, freezing, radiation and chemicals – germination- return to vegetative growth Endospores • Resistance linked to high levels of calcium and dipicolinic acid • Dehydrated, metabolically inactive • thick coat • Longevity verges on immortality - 25,250 million years. • Resistant to ordinary cleaning methods and boiling • Pressurized steam at 120oC for 20-30 minutes will destroy Bacterial Shapes, Arrangements, and Sizes • Variety in shape, size, and arrangement but typically described by one of three basic shapes: – coccus - spherical – bacillus – rod • coccobacillus – very short and plump • vibrio – gently curved – spirillum - helical, comma, twisted rod, • spirochete – spring-like Bacterial Shapes, Arrangements, and Sizes • Arrangement of cells is dependent on pattern of division and how cells remain attached after division: – cocci: • • • • • • singles diplococci – in pairs tetrads – groups of four irregular clusters chains cubical packets – bacilli: • chains • palisades