Fundamentals II: Introduction to Bacteriology and Bacterial Structure Janet Yother, Ph.D. Department of Microbiology jyother@uab.edu 4-9531 Learning Objectives • Fundamental properties of prokaryotes • Basic structures of bacteria • Gram-positive vs Gram-negative bacteria Domains (Kingdoms) Based on evolutionary relationships • Eukaryote (Plants, Animals, Protists, Fungi) • Eubacteria (Eubacteria) • Archaea (Archaea) Distinctive Features of Prokaryotic and Eukaryotic Cells Cell component Prokaryotes Eukaryotes Nucleus No membrane; single, (usually) circular chromosome Membrane-bound; a number of individual chromosomes Extrachromosomal DNA Often present (plasmids, phage) In organelles Organelles in Cytoplasm None Mitochondria (and chloroplasts in photosynthetic organisms) Cytoplasmic Membrane Respiration, secretion, macromolecular synthesis Lacks functions of prokaryotic membrane Cell Wall Peptidoglycan (absent in Mycoplasma) No peptidoglycan (cellulose, chitin in some) Sterols Absent (except in Mycoplasma) Usually present Ribosomes 70S (50S + 30S) 80S (60S + 40S) Bacterial Nomenclature • • • • • • • • • Kingdom Prokaryotae Division Gracilicutes Class Scotobacteria Subclass Order Spirochaetales Family Spirochaetaceae Tribe Genus Borrelia Species Borrelia burgdorferi BACTERIA Prokaryotic Cell Morphology BACTERIAL CELL • 50% protein • 20% nucleic acids (10x more RNA than DNA) • 10% polysaccharides • 10% lipids Bacterial Chromosomes • Single, circular, double-stranded DNA (exception - borrelia = linear) ori C ori C • Replication begins at unique point; bidirectional • Haploid (1 to 4 copies depending on growth rate) • 600 to >5000 kb* in size (smaller = more dependent on host/environment) • Up to 1 mm in length; supercoiled • Contained in nucleoid * ~1 kb/gene Bacterial Nucleoids • Chromosomal DNA (60%; 2-3% dry wt of cell) + RNA (30%) + Protein (10%) • No nuclear membrane • No histones (~6 chromosome-associated basic proteins involved in determining chromosomal structure) • Polyamines (e.g., spermidine and putrescine) neutralize negative charges on phosphates • Haploid chromosome in cytoplasm – 1 to 4 nuclear bodies/cell, number depends on growth rate (faster = more) • Can be membrane-associated (during cell division) Bacillus cereus Light Microscopy 2500x Feulgen strain Jawetz Med Micro 25e Escherichia coli Electron microscopy Extrachromosomal DNA • Plasmids - Replicate in cytoplasm, independent of chromosome. – – – – Double-stranded DNA; usually circular (borrelia = linear) Few to several hundred kb Few to several hundred copies per cell Conjugative (F, R), antibiotic resistance, metabolic, virulence • Bacteriophage - virus; – replicates in cytoplasm or integrates into chromosome – can contribute to virulence into Bacterial Structure Cytoplasmic Membrane • Lipid bilayer – – – – – Permeability barrier Active transport Electron transport Oxidative phosphorylation Photosynthesis • Affected by antibacterials – Detergents – Polymyxins (damage PEcontaining membranes) – Ionophores (disrupt membrane potential) Cell Wall • Shape • Barrier (osmotic resistance) • Comprised of highly crosslinked peptidoglycan • Affected by antibacterials (e.g, b-lactam antibiotics, lysozyme) • Basis for gram-stain Peptidoglycan • Backbone of N-acetyl glucosamine and Nacetyl muramic acid • Cross-linked by peptide bridges at MurNAc http://employees.csbsju.edu/hjakubowski/classes/ch331/cho/peptidoglycan.gif Peptidoglycan http://de.wikipedia.org/wiki/Peptidoglycan Peptidoglycans Transglycosylases [GlcNAc-MurNAc]n (TG) link [GlcNAc-MurNAc]n D-glu D-glu L-lys L-lys (gly)n Amidases (autolysins, e.g.) cleave L-ala L-ala Hydrolases (lysosyme, mutanolysin, e.g.) cleave (gly)n D-ala D-ala Transpeptidases (TP) link. b-lactams resemble TP substrates, block crosslinking of growing chain PG structures vary between/among Gm+ and Gm-. This = Gm+. b-lactams and Peptidoglycan Crosslinking [GlcNAc-MurNAc]n L-ala D-glu L-lys D-ala D-ala non-crosslinked peptidoglycan R Transpeptidase NH O C CH HN CH3 HC CH3 HOOC Terminal D-ala-D-ala CH2 C O NH O C CH N CH S C HC b-lactam ring HOOC (CH3)2 Benzylpenicillin (penicillin G) Gram Stain • Gram’s crystal violet (CV) • Potassium-iodide (KI) • Ethanol - decreases hydration of cell wall • Wash CV-I complexes trapped in thick cell walls (cells remain purple = gram-positive) • Safranin (red) thin cell walls don’t retain CV-I complexes, counterstained with safranin (red = gram-negative) Exceptions to gram-positive / gram-negative staining • Mycoplasmas - no cell wall. • Mycobacteria - lipid interferes with stain – Detected with acid fast stain (carbol fuschin retained following decolorization with HCl/EtOH) Both are related to gram-positives, based on genetic analyses (rRNA sequence) Gram-positives • • • • • Cytoplasmic Membrane Cell wall Lipoteichoic acid Teichoic acid Proteins Gram-positive Cell Walls • Thick peptidoglycan (10 to 100 nm) • Wall teichoic acids (WTA) - repeating units of phosphodiester-linked (negative charge) glycerol or ribitol backbone + side chains (D-ala, glucose). Covalently linked to PG (MurNAc) Bacillus subtilus W23 TA Repeat Ribitol-P Linkage Unit (LU) CH 2 OH O-CH 2 H-C-O-R 1 H-C-OH H-C-O-R 2 O H-O-C-H P O P CH 2 O O-CH 2 H-O-C-H O- OH CH 2 OH O O O O- O CH 2 OH O O P CH 2 O Peptidoglycan HNAc OH HNAc CH 2 P O O O O O - HO GlcNAc- HNAc peptide O(Glycerol-P) CH 2 O 2 -( N-acetylmannosamine )-GlcNAc-P-----MurNAc-GlcNAc-- (n) **Glycerol-P TAs also have linkage unit - R groups differ on R1 = H or Ala; R2 = H or Glc TA repeat and LU Gram-positive Teichoic Acids • Wall Teichoic Acids (WTA) – covalently linked to PG • Lipoteichoic acids (LTA) – similar to WTA but anchored to cytoplasmic membrane lipids; phosphodiester-linked (negative charge) • LTA and WTA • ion binding • charge maintenance • membrane integrity • adherence • anchor proteins • Cell walls - inflammation Gram-negatives • Cytoplasmic membrane • Cell Wall • Outer membrane • Lipopolysaccharide • Proteins Gram-negatives • Cell Wall – Thin peptidoglycan (1 layer; 2 nm) – No WTA or LTA • Periplasmic space - digestive and protective enzymes; transport • Outer membrane (OM) - blocks entry of large molecules (>800 Da). Not typical lipid bilayer. – Attached to PG by lipoprotein – Lipopolysaccharide (LPS) - forms outer leaflet of OM – OM proteins – transport; porins allow passive diffusion of low MW hydrophilic compounds (sugars, amino acids) OmpF Lipopolysaccharide (LPS) • Endotoxin - toxic shock; fever. leukopenia, hypotension, acidosis, DIC, death (OM)-Lipid A --- core polysaccharide --- O Ag toxic properties HM HM MM LM varies with species polysaccharide varies with strain 3 - 4 sugars/repeat Up to 25 repeats serotyping Gram-negative Surface (Cytoplasmic Membrane) Optional Features (Gram +/-) • Capsules - polysaccharide or protein (usually covalently linked to peptidoglycan) – Antiphagocytic (block C3b deposition or recognition), attachment • Surface Proteins - anchored in CM, OM, CW – Antiphagocytic, attachment • Flagella - protein. Rotates to propel cell. Flagella - peitrichous – Motility, chemotaxis, virulence (H-antigen) capsules - colony Flagella - EM capsules - microscope Flagella - unipolar Optional Features (Gram +/-) • Pili - protein. Shorter, narrower than flagella. • Common - peritrichous; attachment • F (sex) - single; gene transfer (conjugation; gram -) • Toxins - excreted; act on host cells; Clostridium botulinum; Vibrio cholerae • Enzymes - hyaluronidase, proteases, DNases • Endospores - dehydrated cells; Clostridium, Bacillus species (gram +) F-pilus