Bacteria

BACTERIA ⦿ Size of Bacteria - 0.2 – 1.5 µm in diameter - 3 – 5 µm in length Diversity of Microorganisms I. Bacteria (Sing. Bacterium) Include two groups:  Eubacteria: Peptidoglycan cell walls.  Archaebacteria: Lack peptidoglycan cell walls. Shapes: Several forms:      Bacilli: Rod like. (Sing. Bacillus) Cocci: Spherical. (Sing. Coccus) Spiral: Corkscrew or curved Square Star shaped Diversity of Microorganisms I. Bacteria (Sing. Bacterium) Divide by binary fission (not mitosis). Source of nutrients varies:  Heterotrophs: Consume organic chemicals.  Autotrophs: Make their own food. Include photosynthetic bacteria. Motility: Many can “swim” by using moving appendages:  Cilia: Small hair like structures  Flagella: Large whip like structures. ⦿ Shape of Bacteria • Cocci – spherical/ oval shaped • Bacilli – rod shaped • Coccobacilli – rods with spherical ends • Vibrios – comma shaped • Spirilla – rigid spiral forms • Spirochetes – flexible spiral forms • Actinomycetes – branching filamentous bacteria Comma shaped Spirilla Spirochetes Coccus Cocci in pair – Diplococcus Tetrad – groups of four Cocci in chain - Streptococci Cocci in cluster - Staphylococci ⦿ Anatomy of Bacterial Cell • Outer layer - two components: 1. Rigid cell wall 2. Cytoplasmic (Cell/ Plasma) membrane – present beneath cell wall • Cytoplasm - gel-like substance enclosed within the cell membrane contains cytoplasmic inclusions, ribosomes, mesosomes and nucleoid • Additional structures - plasmid, slime layer, capsule, flagella, fimbriae (pili) and spores. ⦿ Structure & Function of Cell Components CELL WALL •Outermost layer, encloses cytoplasmic membrane 1. Confers shape and rigidity 2.Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape. 3. Composed of Mucopeptide (peptidoglycan/ murein): formed by N-acetyl glucosamine (NAG) & N-acetyl muramic acid (NAM) alternating in chains, held by peptide chains. 4. Can not be seen by direct light microscopy and do not stain with simple stains. 5. Carries bacterial antigens – important in virulence & immunity. 6. Chemical nature of the cell wall helps to divide bacteria into two broad groups – Gram positive & Gram negative . 7. Gram +ve bacteria have simpler chemical nature than Gram –ve bacteria. 8. Several antibiotics may interfere with cell wall synthesis e.g. Penicillin, Cephalosporins ⦿ Gram positive cell wall • The Gram-positive cell wall is peptidoglycan multilayered cytoplasmic membrane. composed of a thick, sheath outside of the • Teichoic acids are linked to and embedded in the peptidoglycan, and lipoteichoic acids extend into the cytoplasmic membrane Gram negative cell wall • The Gram-negative cell wall is composed of an outer membrane linked to thin single-layered peptidoglycan by lipoproteins. • The peptidoglycan is located within the periplasmic space that is created between the outer and inner membranes. • The outer membrane includes *porins, which allow the passage of small hydrophilic molecules across the membrane, and **lipopolysaccharide molecules that extend into extracellular space. ⦿ Property of bacteria Gram Positive Gram Negative Thickness of wall 20-80 nm 10 nm Number of layers in wall 1 2 Peptidoglycan content >50% 10-20% Teichoic acid in wall + - Lipid & lipoprotein content 0-3% 58% Protein content 0% 9% Lipopolysaccharide 0 13% Sensitive to penicillin Yes Less sensitive Digested by lysozyme Yes Weakly Cytoplasmic (Plasma) membrane • Thin layer 5-10 nm, separates cell wall from cytoplasm. • Acts as a semi-permeable membrane: controls the inflow and outflow of metabolites. • Composed of lipoproteins with small amounts of carbohydrates. Cytoplasm • Colloidal system of variety of organic & inorganic solutes in viscous watery solution = Cytoplasmic Components 1. Ribosomes: 2. Mesosomes: place of protein synthesis (70 S) 1. Multi-laminated structures formed as invaginations of plasma membrane. 2. Principal sites of respiratory enzymes. 3. Coordinate cytoplasmic nuclear & division during binary fission 4. More prominent in Gram +ve bacteria 3. Intracytoplasmic inclusions: Reserve of energy & phosphate for cell metabolism e.g. Metachromatic granules in diphtheria bacilli 4. Nucleus: • No nucleolus • No nuclear membrane • Oval or elongated bodies generally 1 per cell • Genome – single, circular double stranded DNA (one chromosome). • Divides by binary fission =Additional Organelles 1. Plasmid • Extra-nuclear genetic elements consisting of DNA • Transmitted to daughter cells during binary fission • May be transferred from one bacterium to another by conjugation • Not essential for life of the cell • Confer the resistance certain properties e.g. drug resistance because plasmid carries some genes responsible for drug 2. Capsule & Slime layer: • Viscous layer secreted around the cell wall. • Polysaccharide / polypeptide in nature a) Capsule – sharply defined structure, antigenic in nature • Protects bacteria from lytic enzymes • Inhibits phagocytosis • Stained by negative staining using India Ink • Can be demonstrated by Quellung reaction (capsule swelling reaction). b) Slime layer – is loosely associated with the bacterium and can be easily washed off, whereas a capsule is attached tightly to the bacterium and has definite boundaries. 3. Flagella • Long (3 to 12 µm) filamentous surface appendages • Organs of locomotion • Composed of proteins called flagellins • The number and distribution of flagella on the bacterial surface are characteristic for a given species - hence are useful in identifying and classifying bacteria • Flagella may serve as antigenic determinants (e.g. the H antigens of Gram-negative enteric bacteria) • Presence shown by e.g. hanging drop motility preparation test. • Each flagellum consists of 3 1. parts: Filament 2. 3. Hook Basal body Polar/ Monotrichous – single flagellum at one pole Lophotrichous – tuft of flagella at one pole Amphitrichous – flagella at both poles Peritrichous – flagella all over Amphilophotrichous – tuft of flagella at both ends 4. Fimbriae/ Pili • Thin, hair like appendages on the surface of many Gram negative bacteria • 10-20µ long, acts as organs of adhesion (attachment) allowing bacteria to colonize environmental surfaces or cells and resist flushing • Made up of proteins called pilins. • Pili can be of two types A. Common pili - short & abundant B. Sex pili - very long pili & small number (one to six), helps in conjugation (process of transfer of DNA) 5. Spores : • Highly adverse resistant resting stages formed during environment (depletion of nutrients). • Formed inside the parent cell, hence called Endospores • Very resistant to heat, radiation and drying and can remain dormant for hundreds of years. • Formed by bacteria like Clostridium and Bacillus Shape & position of bacterial spore Oval central Spherical central Nonbulging Oval sub terminal Oval sub terminal Oval terminal Spherical terminal Free spore Bulging Character Nucleus Prokaryotes Eukaryotes Nuclear membrane Absent Present Nucleolus Absent Present Chromosome One circular Cell division Cytoplasmic membrane Binary fission One or more paired and linear Mitosis Structure and phospholipid bilayer, Composition lacks sterols phospholipid bilayer containing sterols Function Capable of endocytosis and exocytosis Incapable of endocytosis (phagocytosis and pinocytosis) and exocytosis Character Prokaryotes Eukaryotes Cytoplasm Mitochondria Absent Present Lysosomes Absent Present Golgi apparatus Absent Present Endoplasmic reticulum Absent Present Vacuoles Absent Present Ribosomes 70 S 80 S Character Prokaryotes Eukaryotes Cell Wall Present Animals & Protozoans – Absent Plants, Fungi & Algae Present Peptidoglycan – complex carbohydrate Cellulose or chitin Flagella Flagella/ Cilia Composition Locomotor organelles