Prokaryotes: Bacteria & Archaea Lecture 3 Introduction • 3 Major Bacterial Shapes – Cocci, Bacilli, Spiral-shaped • Prokaryotic Structures – Flagella and Motility – Fimbriae and Pili – Cell Envelope • Glycocalyx • Cell Wall • Cell Membrane – – – – Gram Positive vs Gram Negative Cells Cytoplasm and Bacterial Genome Ribosomes, Inclusions, Granules Bacterial Endospores Three Major Bacterial Shapes • Cocci – round, spherical • Bacilli – rod • Spiral – helical, comma, twisted rod, spirochete Cocci Coccus – single spherical bacteria • Bacteria can also be categorized according to arrangement, or style of grouping. • The greatest variety of arrangement occurs in cocci. • Factors determining arrangement include pattern of division and how the cells remain attached afterward. Diplococci – pair Streptococci – long chain Tetrad – group of four Sarcinae – cubical packet Staphylococci – irregular cluster Bacilli • Divide only in one plane • Have varied forms depending on species: blocky, spindles, clubbed, drumstick, threadlike Diplobacilli – pair Streptobacilli – long chain Coccobacillus – short and plump rod Palisades – cells of a chain remaining partially attached by a small hinge region at the ends Spiral Vibrio – curved Rod, comma Spirillum – 2 or more turns with a rigid helix; external flagella Spirochete – 3 or more turns with a flexible helix; internal flagella • Spirilla are occasionally found in short chains • Spirochetes rarely remain attached after division Pleomorphism: Cells of a single species varying in shapes and sizes Structure of a Typical Bacterial Cell Prokaryotic Flagella • 3 parts - filament - hook - basal body • Made of flagellin protein • Rotates 360º • Used for motility • Outside of cell wall Flagellar Arrangement Flagellar Motility • When flagella rotate counterclockwise, the cell swims forward in runs. • When flagella reverses direction and rotate clockwise, the cell stops and tumbles Bacterial Chemotaxis Chemotaxis: movement in response to a chemical gradient (toward an attractant or to avoid a repellant) Axial Filament • Periplasmic Flagella: internal flagella enclosed in the space between the outer sheath and the cell wall • Found only in Spirochetes • Made of Flagellin protein Fimbriae • Short, fine and numerous fibers • Promote virulence by being involved in Adhesion & Attachment Neisseria gonorrhoeae Escherichia coli Pili • Also called a Sex Pilus • A rigid, tubular structure made from Pilin protein • Found only in Gram (-) Bacteria • Involved in Conjugation: bacterial “mating” process Cell Envelope Glycocalyx • Coating layer outside of the cell wall • Made of proteins & many carbohydrates (very sticky) • 2 types of Glycocalyx - Slime layer (loose) - Capsule (structured) • Involved in Attachment, Resisting Osmolarity changes, Phagocyte avoidance What a difference a Glycocalyx makes! Streptococcus pneumoniae Klebsiella pneumonia Biofilms A complex association that arises from microorganisms growing together and interacting on the surface of a habitat Occur naturally in the environment but in humans can pose a threat when accumulate on catheters, heart valves, hip joints, and teeth. Cell Wall • Determines shape of bacteria • Prevents osmotic lysis • Generally composed of Peptidoglycan (in bacteria) Peptidoglycan A network of polysaccharide chains cross-linked by short peptides that forms the rigid part of bacterial cell walls. • Polymer of 2 glycans - N-acetylglucosamine (NAG) - N-acetylmuramic acid (NAM) • Linked by polypeptides Gram Positive Cell Wall Consists of: • Thick peptidoglycan layer (20-80 nm) • Teichoic and lipoteichoic acids • Narrow Periplasmic Space • Cell membrane Gram Negative Cell Wall Consists of: • An outer membrane that contains lipopolysaccharide (LPS) • Thin peptidoglycan layer (8-11 nm) • Extensive Periplasmic Space • Inner cell membrane Gram (+) vs. Gram (-) The Gram Stain Plasma Membrane • Phospholipid bilayer with proteins and carbohydrates • Selectively permeable • No sterols in Prokaryotes (except Mycoplasma) • Involved in Transport of molecules • Involved in Metabolic Activity Atypical Cell Walls and/or Membranes • Bacteria without cell walls - Mycoplasma – Have only a cell membrane containing sterols for strength • Bacteria with some peptidoglycan and a lot of mycolic acid - Mycobacterium • Archaea have protein cell walls, polysaccharide cell walls or no cell wall at all. – No Peptidoglycan Cytoplasm • Dense gelatinous solution of sugars, amino acids, & salts (70-80% water) • Nucleoid: a central area in the cell where the bacterial chromosome aggregates • Ribosomes • Inclusions & Granules Bacterial Genome 1. Bacterial Chromosome 2. Plasmids • Single (One Copy) • Small • Circular DNA • Circular DNA • Double Helix • • Codes for all essential genes Genes not essential for cell growth but can code for genes for adaptive traits • Can be transmissible to other bacteria • Can contain genes that provide antibiotic resistance. Ribosomes • Made of ribosomal RNA & protein • Prokaryotic differ from eukaryotic ribosomes in size • Site of protein synthesis • All cells have ribosomes Inclusions & Granules • Inclusions: intracellular storage of metabolic products • Vary in size, number & content • Granules: contain crystals or inorganic compounds Magnetotactic Bacteria Purple Sulfur Bacteria Bacterial Endospores • Resting, dormant cells • Only produced by three G+ genera: Clostridium, Bacillus & Sporosarcina • Have a 2-phase life cycle – vegetative cell & an endospore - sporulation - germination Endospores • Dehydrated, metabolically inactive • Spore coat • Extraordinarily resistant and long lasting