Bacterial Form and Function Microbiology- Ch. 4 pp 87-101

Structure of a Prokaryotic Cell

Prokaryote Structures: Appendages- flagella, pili, fimbrae Cell envelope- glycocalyx, cell wall , cell membrane 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 Stab line in semisolid motility agar growth out from the streak line indicates motility. A= motile; B=nonmotile Motility plate 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: 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. 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 Gram variable 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 Gram-positive bacteria-prominent 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 70S 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: palisades