PHA112 Micro 3 (Structure)2020.pdf

MPharm Programme Microbial Structure Dr Callum Cooper [email protected] Learning Objectives Describe general details of bacterial morphology and provide specific examples Describe general details of bacterial cell structures Internal subcellular structures External structures Describe g...

MPharm Programme Microbial Structure Dr Callum Cooper [email protected] Learning Objectives Describe general details of bacterial morphology and provide specific examples Describe general details of bacterial cell structures Internal subcellular structures External structures Describe general details of viral morphology and structures Bacterial cell structure: What do we need to know? Morphology (structure) Colonies Individual cell Internal components External components How these can relate to physiology and pathogenicity Bacterial cell structure: Morphology On a large scale bacteria form colonies Aggregates of individual bacteria Can take on different shapes, colours, sizes Depends on species Can be used as a very inaccurate form of classification Bacterial cell structure: Morphology Huge variety of different bacterial cell shapes; Size ranges from 1 to 10µm Have to be observed under a microscope Cocci (spheres) Bacilli (Rodshaped) Spiral bacteria Bacterial cell structure: Cocci Monococcus- single cells e.g. Micrococcus flavus Diplococcus- paired cells e.g. Nisseria gonorrhoeae Staphylococci: grouped cells e.g Staphylococcus aureus Bacterial cell structure: Cocci Streptococci: chained cells e.g. Streptococcus pyogenes Tetrads: groups of 4 cocci in the same plane e.g. Micrococcus luteus Sarcina : cuboidal arrangements of 8 cocci Bacterial cell structure: Cocci Diplococcus Tetracoccus Monococcus Bacterial cell structure: Bacilli Bacillus: Single rod e.g Bacillus cereus Diplobacilli: Two Bacilli side by side e.g Coxiella burnetii Streptobacilli: Chains of Bacilli e.g. Streptobacillus moniliformis (Rat Bite Fever) Bacterial cell structure: Spiral bacteria Spirellum: A rigid spiral Gramnegative bacterium e.g. Campylobacter jejuni or Helicobacter pylori Spirochete: thin, long more flexible e.g Treponema pallidium Bacterial cell components: Overview Prokaryotic cells are simpler in structure than eukaryotic cells Share some features but vary in others WILL ONLY FOCUS ON THE DIFFERENCES Bacterial cells can adapt more readily to environmental changes than eukaryotic cells Ability to metabolise wider range of substrates Bacterial cell components: General Bacterial cell components can be broken into the following general categories; Structural Genetic material Ribosomes Motility Nucleoid Plasmid Protein production Cell wall Plasma membrane Flagella Pilli Specialist structures Endopores Capsules and Slime Bacterial external cell components: Cell wall Nearly all bacteria have a cell wall (peptidoglycan) Provides shape Protects against osmotic lysis Bacteria can be divided into two major groups depending on structure; Gram positive cells have a single plasma membrane Gram negative have two plasma membranes Cell surface OM PG PPS IM Gram Positive Gram Negative Cytoplasm Bacterial external cell components: Peptidoglycan Peptidoglycan is a polymer of sugar and amino acids Alternating residues of β-(1,4) linked Nacetylglucosamine (NAG) and Nacetylmuramic acid (NAM). Attached to NAM is a chain of 3 to 5 amino acids. Peptidoglycan layer lets particles ≤~2nm through in both Gram Positive and Gram negative Layer varies in thickness between Gram Positive and Gram Negative 90% of cell weight in Gram Positive 10% of cell weight in Gram Negative Gram Negative Gram Positive PG Bacterial external cell components: Plasma membrane Comprises of; Lipid bilayer Proteins Lipopolysaccharide (Gram Neg) Retains cytoplasm and segregates internal environment Provides support for proteins Selectively permeable Plasma membrane: Lipid Bilayer Comprises of Amphipathic phospholipids Hydrophilic “head points towards external environment Hydrophobic fatty acid “tail” towards bilayer centre NO sterols (e.g. cholesterol) Pentacyclic hopanoids Plasma membrane: Membrane proteins Two main types of proteins; Integral proteins Integral proteins Peripheral proteins ~75% of membrane proteins Tightly attached or stretched across lipid bilayer Functions include ion transport Peripheral proteins ~25 % of membrane proteins Aqueous solubility Cholesterol oxidases (depletes eukaryotic cells of cholesterol) Plasma membrane: Lipopolysaccharide Lipopolysaccharide (LPS) contributes to structural integrity of bacterial cells Can stimulate a pro-inflammatory immune response Consists of 3 domains O antigen Core antigen Lipid A Small amounts can cause illness Endotoxemia → septic shock LPS content highly controlled in sterile manufacturing Limulus amebocyte lysate (LAL) assay By Mike Jones - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10422301; By Asturnut (talk) - I (Asturnut (talk)) created this work entirely by myself., CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=27534108 Bacterial external cell components: Flagella Involved in bacterial motility (movement) Positioning and quantity of flagella are dependent on species Most commonly; Monotrichous (e.g. V. cholerae) Lophotrichous Amphitrichous Peritrichous (e.g. E. coli) Long compared to bacterial cell (~10µm) Powered by H+ flow (occasionally Na+) Involved in pathogenesis Crucial for virulence of V. cholerae Flagella propel H. pylori through mucus lining in stomach Bacterial external cell components: Pilli Can also be known as Fimbriae Found mainly in Gram negative bacteria Two main types; Conjugative pili (allows transfer of DNA between 2 bacteria) Type IV pili (can generate twitching motility) Bacterial external cell components: Capsules and Slime layers Usually comprised of polysaccharides Exact composition varies by species (e.g. D-glutamic acid capsule in B. anthracis) If organised and permanent = Capsule If loosely formed = Slime layer Not required for in vitro growth Has to be induced Can help in attachment to surfaces Protection from adverse conditions Bacterial internal cell components: Nucleoid Main component of bacterial genetic material Not membrane bound Single chromosome of double stranded DNA Bacterial genome of approx. 0.6-10Mbp (human genome 3000Mbp) RNA and protein also present DNA highly coiled and wrapped around nucleoid proteins NOT the same as histones Bacterial internal cell components: Plasmids Extra chromosomal pieces of DNA Can replicate autonomously within the host Can vary in size between 1- >200Kbp Can sometimes be present in Eukaryotic cells Can be transferred between cells Often only contain non-essential genes; Antibiotic resistance Virulence characteristics (e.g. pXO1 in B. anthracis) Bacterial internal cell components: Ribosomes Ribosomes are sites of protein synthesis Bacterial ribosomes contain 2 subunits Small 30S Large 50S Different to Eukaryotic ribosomes (size, sequence and structure) make them a target for antibiotics Bacterial endospores Ability to form spores exists in some bacterial species Sporulation triggered by adverse conditions (e.g lack of nutrients) Most notably Bacillus spp. and Clostridial spp. Acts as a survival mechanism increasing resistance to Temperature, pH, chemical biocides etc Metabolically inert Important in some human disease Clostridium difficile associated diarrhoea (CDAD) Anthrax (caused by B. anthracis) Can be viewed using phase contrast microscopy or stained Bacterial cell structure: Multicellular microorganisms Chains of cells forming long filaments Trichomes (e.g. cyanobacteria) Cells remain attached following cell division Cells separated by cross-walls (septa) Hyphae (e.g. Streptomycetes) Tube-like filaments which may or may not have septa (crosswalls) - i.e. cytoplasm may be continuous May form a dense mycelial mat cf. filamentous fungi Close spatial and physiological relationships allow specialization Viral Structures Simpler than bacterial or fungal cell structures; Genetic material Protein coat Receptors Lipid envelope (optional) Viruses can also infect prokaryotes Bacteriophages Phages are non-pathogenic Useful model organism Most bacteriophages (~95%) belong to the Caudovirales Myoviridae Siphoviridae podoviridae Viral Structures Summary Definition of different bacterial structures Important components of bacterial cell and their roles Introduced viral structures Extra reading Prescotts Microbiology: Parts I; sections 3 & 5 Brock Microbiology Part I; section 2