Bacterial Structure and Growth A.Bacterial Cells: An Overview B.Bacterial Cell Structures C.Factors that Influence Bacterial Growth

A.Bacterial Cells: An Overview Shapes & Arrangements –Round Bacteria Coccus Staphylococcus Diplococcus Tetrad Streptococcus Sarcina –Rod-shaped Bacteria Bacillus Streptobacillus Diplobacillus Coryneform bacteria

A.Bacterial Cells: An Overview Shapes & Arrangements (cont.) –Curved & Spiral Bacteria Vibrio Spirillum Spirochaete

A.Bacterial Cells: An Overview Sizes –Typically ~  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

A.Bacterial Cells: An Overview

B.Bacterial Cell Structures 1. Capsules 2. Cell Wall 3. Plasma Membrane 4. Cytoplasm & Cytoplasmic Inclusions 5. Ribosomes 6. Bacterial DNA 7. Pili 8. Flagella 9. Spores

B. 1. Capsules The cell capsule is a very large structure of some prokaryotic cells, such as bacterial cells. It is a polysaccharide layer that lies outside the cell envelope of bacteria, and is thus deemed part of the outer envelope of a bacterial cell. It is a well-organized layer, not easily washed off, and it can be the cause of various diseases.prokaryotic cellspolysaccharidecell envelopebacteria

B. 1. Capsules The capsule—which can be found in both Gram- negative bacteria and Gram-positive bacteria should not be confused with the second lipid membrane (or bacterial outer membrane), which contains lipopolysaccharides and lipoproteins and is found only in Gram-negative bacteria. When the amorphous viscid secretion (that makes up the capsule) diffuses into the surrounding medium and remains as a loose undemarcated secretion, it is known as slime layer.Gram- negative bacteriaGram-positive bacteriabacterial outer membranelipopolysaccharideslipoproteinsslime layer

B. 1. Capsules (cont.) Functions The capsule is considered a virulence factor because it enhances the ability of bacteria to cause disease (e.g. prevents phagocytosis). The capsule can protect cells from engulfment by eukaryotic cells, such as macrophages. A capsule-specific antibody may be required for phagocytosis to occur.

B. 1. Capsules (cont.) Capsules also contain water which protects the bacteria against desiccation. They also exclude bacterial viruses and most hydrophobic toxic materials such as detergents. Capsules also help cells adhere to surfaces.

B. 2. Cell Wall Gram Staining –Method developed by Gram in 1888 –Gram-positive cells stain purple Gram-negative cells stain pink –Later, it was discovered that the major factor determining Gram reactions is the bacterial cell wall structure –“Gram-positive” & “Gram-negative” These terms can mean either: Staining results, or Types of cell wall structure

B. 2. Cell Wall Peptidoglycan Structure Murein is a unique type of peptidoglycan, a polymer of disaccharides (glycan) cross- linked by short chains of amino acids (peptide). Many types of peptidoglycan exist. All Bacterial peptidoglycans contain N-acetylmuramic acid, which is the definitive component of murein.

B. 2. Cell Wall The cell walls of Archaea may be composed of protein, polysaccharides, or peptidoglycan-like molecules, but never do they contain murein. This feature distinguishes the Bacteria from the Archaea.

B. 2. Cell Wall Gram-positive Cell Wall In the Gram-positive Bacteria (those that retain the purple crystal violet dye when subjected to the Gram-staining procedure), the cell wall consists of several layers of peptidoglycan. Running perpendicular to the peptidoglycan sheets is a group of molecules called teichoic acids which are unique to the Gram-positive cell wall.

B. 2. Cell Wall -Gram-negative Cell Walls In the Gram-negative Bacteria (which do not retain the crystal violet), the cell wall is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane. The outer membrane of Gram-negative bacteria invariably contains a unique component, lipopolysaccharide (LPS or endotoxin), which is toxic to animals. In Gram-negative bacteria the outer membrane is usually thought of as part of the cell wall.

B. 2. Cell Wall Variations on Cell Wall Architecture –Acid-fast Cell Walls Similar to Gram-positive structure, but have Mycolic Acid: A waxy lipid Require special acid-fast staining technique Includes Mycobacterium and Nocardia

B. 2. Cell Wall Variations on Cell Wall Architecture (cont.) –Mycoplasmas Bacteria that are naturally have no cell walls Includes Mycoplasma and Ureaplasma –Archaeobacteria Have unusual archaeobacterial cell walls with no peptidoglycan Have unusual metabolisms Share a more recent common ancestor with eukaryotes than with eubacteria (“true bacteria”)

B. 3. Plasma Membrane Structure –Phospholipid Bilayer with Associated Proteins Functions –Maintain Cell Integrity –Regulate Transport –Specialized Functions in Bacteria

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

B. 5. Ribosomes bacteria contain ribosomes, often grouped in chains called polyribosomes, for the production of proteins, but the structure of the bacterial ribosome is different from that of eukaryotes and Archaea.

B. 5. Ribosomes Bacterial ribosomes have a sedimentation rate of 70S (measured in Svedberg units): their subunits have rates of 30S and 50S. Some antibiotics bind specifically to 70S ribosomes and inhibit bacterial protein synthesis. Those antibiotics kill bacteria without affecting the larger 80S ribosomes of eukaryotic cells and without harming the host.

B. 6. Bacterial DNA Genetic information in bacteria is stored in the sequence of DNA in two forms, that is bacterial chromosome and plasmid.

B. 6. Bacterial DNA The following are the properties of a bacterial chromosome 1-Location: Within nucleoid region, not surrounded by nuclear envelope 2-Number: 1 chromosome each cell

B. 6. Bacterial DNA 3-Component: Single, double stranded, circular DNA. Also contains RNA and proteins that take part in DNA replication, transcription and regulation of gene expression. DNA does not interact with protein histone. 4-Information: Contain genes essential for cellular functions.

B. 6. Bacterial DNA In addition to chromosome, bacterial cells may also contain another genetic element, plasmid

B. 6. Bacterial DNA Features of plasmid Location: In cytosol of bacterial cells-1 Number: From 1 to several-2 Size: Much smaller than chromosomes-3 4-Components: Single, double stranded, circular DNA 5-Information: Contains drug resistant genes as well as heavy metal resistant genes. Not essential for growth and metabolism of bacteria.

B. 7. Pili Hair-like structures on cell surface Functions –Attachment –Conjugation

B. 8. Flagella Function –Motility Almost all motile bacteria are motile by means of flagella Structure –Filament Composed of the protein flagellin –Hook & Rotor Assembly Permits rotational "spinning" movement

B. 8. Flagella Mechanism of Motility –“Run and Tumble” Movement controlled by the direction of the flagellar spin –Counterclockwise spin = Straight Run Clockwise spin = Random Tumble

B. 8. Flagella Chemotaxis –Response to the concentration of chemical attractants and repellants –As a bacterium approaches an attractant: the lengths of the straight runs increase –As a bacterium approaches a repellant: the lengths of the straight runs decrease

B. 9. Spores Function –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 spores Occurrence –Produced by very few genera of bacteria –Major examples Bacillus Clostridium

B. 9. Spores Significance in Medicine & Industry –Spores are resistant to killing –Cannot be killed by 100°C (boiling) –Requires heating to 120°C for min (autoclaving or pressure cooking)

B. 9. Spores Sporulation –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

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

C.Factors that Influence Bacterial Growth Growth vs. Survival –Bacteria may tolerate or survive under more extreme conditions than their growth conditions

C.Factors that Influence Bacterial Growth Nutrient Requirements –Energy Source Most bacteria are chemotrophs; a few are phototrophs –Carbon Source Most bacteria are heterotrophs; a few are autotrophs –Nitrogen, Phosphate, Sulfur, Trace Minerals

C.Factors that Influence Bacterial Growth Nutrient 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

C.Factors that Influence Bacterial Growth Temperature –Psychrophiles Grow at ~0°C - 20°C –Mesophiles Grow at ~20°C - 45°C –Moderate Thermophiles Grow at ~45°C - 70°C –Extreme Thermophiles Grow at ~70°C - 100°C

C.Factors that Influence Bacterial Growth pH –Acidophiles Grow at ~pH pH 6.0 –Neutrophiles Grow at ~pH pH 8.5 –Alkalophiles Grow above pH 8.5

C.Factors that Influence Bacterial Growth Oxygen –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

C.Factors that Influence Bacterial Growth Oxygen (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

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