IV.Bacterial Structure and Growth

A.Bacterial Cells: An OverviewB.Bacterial Cell StructuresC.Factors that Influence Bacterial Growth

IV. A.Bacterial Cells: An OverviewShapes & ArrangementsRound BacteriaCoccus StaphylococcusDiplococcus Tetrad Streptococcus Sarcina Rod-shaped BacteriaBacillus StreptobacillusDiplobacillus Coryneform bacteria

IV. A.Bacterial Cells: An OverviewShapes & Arrangements (cont.)Curved & Spiral BacteriaVibrio Spirillum Spirochaete

IV. A.Bacterial Cells: An OverviewSizesTypically ~ 0.1 - 20 m (with some exceptions)Typical coccus: ~ 1 m (eg Staphylococcus)Typical short rod: ~ 1 x 5 m (eg E. coli)Barely within the best resolution of a good compound light microscope

IV. A.Bacterial Cells: An Overview

IV. B.Bacterial Cell Structures1.Capsules2.Cell Wall3.Plasma Membrane4.Cytoplasm & Cytoplasmic Inclusions5.Ribosomes6.Bacterial DNA7.Pili8.Flagella9.Spores

IV. B. 1.CapsulesSpecies and strain specific Structure Polysaccharide or polypeptide layer outside cell wall May be tightly or loosely bound Detected by negative staining techniques

IV. B. 1.Capsules (cont.)Functions Attachment Resistance to desiccation Nutrient Storage Evasion of phagocytosis eg. in Streptococcus pneumoniae S strain is encapsulated & virulent R strain is nonencapsulated & nonvirulent

IV. B. 2.Cell WallGram StainingMethod developed by Gram in 1888Gram-positive cells stain purple Gram-negative cells stain pinkLater, it was discovered that the major factor determining Gram reactions is the bacterial cell wall structureGram-positive & Gram-negativeThese terms can mean either:Staining results, or Types of cell wall structure

IV. B. 2.Cell Wall Peptidoglycan StructureComposition A Polysaccharide Composed of alternating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)Peptide Crosslinking Between NAM units Much thicker and more crosslinking in Gram-positive than in Gram-negative Bacteria

IV. B. 2.Cell Wall

Gram-positive Cell WallThick Layer of Highly Crosslinked Peptidoglycan Teichoic Acid Strands

IV. B. 2.Cell WallGram-negative Cell WallsOuter Membrane Lipopolysaccharide Layer containing Lipid A Phospholipid Layer Outer Membrane Proteins Thin Layer of Peptidoglycan with no teichoic acid Periplasmic Space

IV. B. 2.Cell WallVariations on Cell Wall ArchitectureAcid-fast Cell WallsSimilar to Gram-positive structure, but have Mycolic Acid: A waxy lipidRequire special acid-fast staining techniqueIncludes Mycobacterium and Nocardia

IV. B. 2.Cell WallVariations on Cell Wall Architecture (cont.)MycoplasmasBacteria that are naturally have no cell wallsIncludes Mycoplasma and UreaplasmaArchaeobacteriaHave unusual archaeobacterial cell walls with no peptidoglycanHave unusual metabolismsShare a more recent common ancestor with eukaryotes than with eubacteria (true bacteria)

IV. B. 3.Plasma MembraneStructurePhospholipid Bilayer with Associated Proteins Functions Maintain Cell Integrity Regulate Transport Specialized Functions in Bacteria

IV. B. 4.Cytoplasm & Cytoplasmic InclusionsComposition: Viscous aqueous suspension of proteins, nucleic acid, dissolved organic compounds, mineral saltsCytoplasmic Inclusions:Metachromatic Granules (Phosphate) Starch Granules Lipid Droplets Sulfur Granules

IV. B. 5.RibosomesSuspended in CytoplasmSites of Protein Synthesis

IV. B. 6.Bacterial DNAChromosomal DNA Plasmid DNA R-Plasmids F-Plasmids

IV. B. 7.PiliHair-like structures on cell surface Functions Attachment Conjugation

IV. B. 8.FlagellaFunctionMotility Almost all motile bacteria are motile by means of flagellaMotile vs. nonmotile bacteriaStructureFilament Composed of the protein flagellinHook & Rotor Assembly Permits rotational "spinning" movement

IV. B. 8.Flagella

Mechanism of MotilityRun and Tumble Movement controlled by the direction of the flagellar spinCounterclockwise spin = Straight Run Clockwise spin = Random Tumble

IV. B. 8.FlagellaChemotaxisResponse to the concentration of chemical attractants and repellantsAs a bacterium approaches an attractant: the lengths of the straight runs increaseAs a bacterium approaches a repellant: the lengths of the straight runs decrease

IV. B. 9.SporesFunction To permit the organism to survive during conditions of desiccation, nutrient depletion, and waste buildup Bacterial spores are NOT a reproductive structure, like plant or fungal sporesOccurrence Produced by very few genera of bacteria Major examples Bacillus Clostridium

IV. B. 9.SporesSignificance in Medicine & Industry Spores are resistant to killing Cannot be killed by 100C (boiling) Requires heating to 120C for 15-20 min (autoclaving or pressure cooking)

IV. B. 9.SporesSporulation The process of spore formation Governed by genetic mechanism A copy of the bacterial chromosome is surrounded by a thick, durable spore coat This forms an endospore within a vegetative cell When the vegetative cell dies and ruptures, the free spore is released

IV. B. 9.SporesSpore Germination When a spore encounters favorable growth conditions The spore coat ruptures and a new vegetative cell is formed

IV. C.Factors that Influence Bacterial GrowthGrowth vs. SurvivalBacteria may tolerate or survive under more extreme conditions than their growth conditions

IV. C.Factors that Influence Bacterial GrowthNutrient RequirementsEnergy Source Most bacteria are chemotrophs; a few are phototrophs Carbon Source Most bacteria are heterotrophs; a few are autotrophs Nitrogen, Phosphate, Sulfur, Trace Minerals

IV. C.Factors that Influence Bacterial GrowthNutrient Requirements (cont.)Special Requirements examples: amino acids and enzyme cofactors (vitamins) Fastidious bacteria: Strains that are difficult or impossible to culture due to special growth requirements

IV. C.Factors that Influence Bacterial GrowthTemperaturePsychrophiles Grow at ~0C - 20C Mesophiles Grow at ~20C - 45C Moderate Thermophiles Grow at ~45C - 70C Extreme Thermophiles Grow at ~70C - 100C

IV. C.Factors that Influence Bacterial GrowthpHAcidophiles Grow at ~pH 1.0 - pH 6.0 Neutrophiles Grow at ~pH 6.0 - pH 8.5 Alkalophiles Grow above pH 8.5

IV. C.Factors that Influence Bacterial GrowthOxygen Strict aerobes (Obligate aerobes) Use oxygen for respiration in their metabolism Require the presence of a normal oxygen concentration (~20%) for growth Strict anaerobes (Obligate anaerobes) Oxygen is a poison for these microbes Cannot grow at all in the presence of oxygen

IV. C.Factors that Influence Bacterial GrowthOxygen (cont.)Aerotolerate anaerobes Do not use oxygen, but oxygen is not a poison for these Can grow equally well with or without oxygen Facultative anaerobes Use oxygen for respiration, but can also grow without oxygen Grow better with oxygen that without oxygen

IV. C.Factors that Influence Bacterial GrowthOxygen (cont.) Microaerophiles Require low concentrations (~5% - 10%) of oxygen for growth