Bacterial Types Lecture 1

By Dr. Mohamed Naguib Mohamed Associate Professor of Microbiology  Bacterial types Monomorphic (maintain a single shape) Some of the most deadly bacterial diseases, including leprosy, anthrax and plague, are caused by bacterial lineages with extremely low levels of genetic diver...

By Dr. Mohamed Naguib Mohamed Associate Professor of Microbiology  Bacterial types Monomorphic (maintain a single shape) Some of the most deadly bacterial diseases, including leprosy, anthrax and plague, are caused by bacterial lineages with extremely low levels of genetic diversity, the so-called ‘genetically monomorphic bacteria’. It has only become possible to analyze the population genetics of such bacteria since the recent advent of high- throughput comparative genomics. The genomes of genetically monomorphic lineages contain very few polymorphic sites.  Bacterial types or Pleomorphic (can have many shapes) Pleomorphic bacteria are those, which shows variable shape and size in a response to changing environmental conditions (ie. they can be rod shaped in a particular environment and in next moment they may be of coccoid shaped). eg. Deinococcus, Helicobacter pylori, Mycoplasma etc.  Cocci 1- Monococci 2- Diplococci: The cocci are arranged in pairs. Examples: Neisseria gonorrhoeae. 3- Streptococci: The cocci are arranged in chains, as the cells divide in one plane. Example: Streptococcus pyogenes. 4-Tetrads: The cocci are arranged in packets of four cells, as the cells divide in two plains. Examples: Aerococcus, Pediococcus and Tetragenococcus. 5- Sarcinae: The cocci are arranged in a cuboidal manner, as the cells are formed by regular cell divisions in three planes. Cocci that divide in three planes and remain in groups cube like groups of eight. Examples: Sarcina ventriculi, Sarcina ureae, etc. 6. Staphylococci: The cocci are arranged in grape-like clusters formed by irregular cell divisions in three plains. Examples: Staphylococcus aureus Bacilli  Bacilli Bacilli divide only across their short axis, so there are fewer groupings of bacilli than of cocci. a) Single bacilli (Most Bacilli): appear as single rods. Example: Bacillus cereus. b) Diplobacilli pairs: appear in pairs after division, Examples : Coxiella burnetii, Moraxella bovis, Klebsiella rhinoscleromatis, etc c) Streptobacilli appear in chains. Examples: Streptobacillus moniliformis D) Coccobacilli appear so short and stumpy that they appear ovoid. They look like coccus and bacillus. Examples: Haemophilus influenza.  Bacilli E) Palisades: The bacilli bend at the points of division following the cell divisions, resulting in a palisade arrangement resembling a picket fence and angular patterns that look like Chinese letters. Example: Corynebacterium diphtheriae F) Spore former Spore-forming bacteria include Bacillus (aerobic) and Clostridium (anaerobic) species.  Arrangement of Spiral Bacteria Spirilla (or spirillum for a single cell) are curved bacteria which can range from a gently curved shape to a corkscrew-like spiral. Many spirilla are rigid and capable of movement. A special group of spirilla known as spirochetes are long, slender, and flexible. 1. Vibrio They are comma-shaped bacteria with less than one complete turn or twist in the cell. Example: Vibrio cholerae  Arrangement of Spiral Bacteria 2. Spirilla They have rigid spiral structure. Spirillum with many turns can superficially resemble spirochetes. They do not have outer sheath and endoflagella, but have typical bacterial flagella. Example: Campylobacter jejuni, Helicobacter pylori, Spirillum winogradskyi, etc.  Arrangement of Spiral Bacteria 3. Spirochetes Spirochetes have a helical shape and flexible bodies. Spirochetes move by means of axial filaments, which look like flagella contained beneath a flexible external sheath but lack typical bacterial flagella. Examples: Leptospira species (Leptospira interrogans), Treponema pallidum, Borrelia recurrentis, etc.  Bacterial cells Bacterial cells lack a membrane bound nucleus. Their genetic material is naked within the cytoplasm. Ribosomes are their only type of organelle. The term “nucleoid” refers to the region of the cytoplasm where chromosomal DNA is located, usually a singular, circular chromosome. Bacteria are usually single-celled, except when they exist in colonies.  Cell Wall A wall located outside the cell membrane provides the cell support, and protection against mechanical stress or damage from osmotic rupture and lysis. The major component of the bacterial cell wall is peptidoglycan or murein. This rigid structure of peptidoglycan, specific only to prokaryotes, gives the cell shape and surrounds the cytoplasmic membrane. Peptidoglycan is a huge polymer of disaccharides (glycan) cross-linked by short chains of identical amino acids (peptides) monomers.  Cell Wall The backbone of the peptidoglycan molecule is composed of two derivatives of glucose: N-acetylglucosamine (NAG) and N- acetlymuramic acid (NAM) with a pentapeptide coming off NAM and varying slightly among bacteria. The NAG and NAM strands are synthesized in the cytosol of the bacteria. They are connected by inter-peptide bridges. They are transported across the cytoplasmic membrane by a carrier molecule called bactoprenol.  Cell Wall From the peptidoglycan inwards all bacterial cells are very similar. - The bacterial world divides into two major classes: Gram positive (Gram +) and Gram negative (Gram-). - The cell wall provides important ligands for adherence and receptor sites for viruses or antibiotics. Gram-Positive bacteria  Gram-Positive Cell Walls Many layers of peptidoglycan. + teichoic acids. repeating disaccharide attached by polypeptides. Lipoteichoic acid, links peptidoglycan to the plasma membrane wall teichoic acid, linked to the peptidoglycan layer. Gram-negative bacteria  Gram-Negative Cell Walls One layer of peptidoglycan + an outer membrane. (lipopolysaccharides (LPS), lipoproteins, and phospholipids) protects the cell from phagocytosis and from penicillin, lysozyme, and other chemicals. Periplasmic Space/ periplasm a gel-like fluid between the outer membrane and the plasma membrane. contains a high concentration of degradative enzymes and transport proteins. Characteristics Gram Positive Gram Negative Gram reaction Retain crystal violet dye and Can be decolorized to accept stain blue or purple counterstain (safranin)and stain pink or red Peptidoglycan layer Thick (multilayered) Thin (Single layered) Teichoic acids Present in many Absent Periplasmic space Absent Present Outer membrane Absent Present Lipopolysaccharides (LPS) Virtually none High content Lipid and Lipoprotein Low (Acid fast bacteria have High (because of presence of content lipid linked to peptidoglycan) outer membrane) Flagellar structure 2 rings in basal body 4 rings in basal body Toxins produced Exotoxins Endotoxins and exotoxins Gram Stain  Gram Stain The crystal violet–iodine complex combines with peptidoglycan. The decolorizer removes the lipid outer membrane of gram-negative bacteria and washes out the crystal violet.  Acid-Fast Stain The acid-fast stain is a laboratory test that determines if a sample of tissue, blood, or other body substance is infected with the bacteria that causes tuberculosis (TB) and other illnesses. Acid-Fast Stain Acid-Fast Stain  Acid-Fast Stain Binds strongly only to bacteria that have a waxy material in their cell walls. Acid-fast cell walls have a layer of mycolic acid outside a thin peptidoglycan layer. Used to distinguish Mycobacterium. Carbolfuchsin (red dye), heating, Washing with water, Treating with acid-alcohol (decolorizer/ removes the stain from non-acid-fast Bacteria)  Atypical Cell Walls 1- Mycoplasma :have NO cell walls Their plasma membranes are unique among bacteria in having lipids called sterols, which are thought to help protect them from lysis(rupture).  Atypical Cell Walls 2- Archaea (survive extremely harsh environments)walls composed of polysaccharides and proteins, but NOT peptidoglycan, Pseudomurein instead. 3 Types: Methanogens, Halophiles, & Thermophiles (optimum temp.= 70°C).  Plasma (Cytoplasmic) Membrane Phospholipids Bilayer& Proteins "fluid mosaic model" peripheral proteins - lie at the inner or outer surface of the membrane easily removed from the membrane by mild treatments may function as enzymes that catalyze chemical reactions, as a “scaffold” for support, and as mediators of changes in membrane shape during movement. Integral proteins proteins penetrate the membrane completely and are called transmembrane proteins channels that have a pore, or hole, through which substances enter and exit the cell can be removed from the membrane only after disrupting the lipid bilayer(by using detergents, for example).  Plasma (Cytoplasmic) Membrane Plasma membrane is selectively permeable.-Can be Damaged by alcohols.-Plasma membrane Functions: - Osmotic barrier. - Concentrate nutrients w/i the cell. - Site for Biosynthesis of cell wall and capsule compounds. - Locate certain enzymes (for breakdown of Food..)and organelles (E.g. Ribosomes). - Presence of Chromatophores, involved in photosynthesis.  Movement of Materials across Membranes: Passive (No energy required): from areas of higher to lower concentration - Simple diffusion - Facilitated diffusion - Osmosis Active (Require energy): from areas of low to high concentration - Group translocation  Capsules Gelatinous polysaccharide that surround cells. Enable adherence to surfaces (and bacterial infection/Virulence!), prevent desiccation, and may provide nutrients. Presence of a capsule can be determined by using negative staining. protect pathogens from phagocytosis. - S smooth capsules: Pathogenic. - R Rough capsules: Non-pathogenic. Streptococcus pneumoniae causes pneumonia Streptococcus mutans causes dental caries Bacillus anthracis (produces a capsule of d-glutamic acid) cause anthrax  Motility Some bacteria are motile, other are nonmotile. Flagella: long filamentous appendages consisting of a filament, hook, and basal body. Atrichous: Bacteria that lack flagella. If Flagella is present, it can be divided according to Numberand Arrangement into: Peritrichous: Distributed over the entire cell Monotrichous: A singleflagellum at one pole. Lophotrichous: A tuftof flagella coming from one pole. Amphitrichous: At both poles. Flagella is originated fromthe Cytoplasm (Not the cell wall).  Pili - Involved in Attachment, and transfer of DNA rather than for motility. - Shorter than flagella. - NOT originated from the cell wall. - Extends by the addition of subunits of pilin. E.g. in Neisseria gonorrhoeae  Cytoplasm The substance of the cell inside the plasma membrane 80% water, 20% proteins (enzymes), carbohydrates, lipids, inorganic ions, & glycogen. - Thick, aqueous, semitransparent, and elastic Ribosomes-70S ribosomes; consist of rRNAand protein.- - Function: Protein synthesis. Nucleoid :contains a single long, continuous, and - frequently circularly arranged thread of DNA (bacterial chromosome). Not enveloped, No histones. Plasmids (5 to 100genes)small, circular, double-stranded DNA molecules in bacteria. Function: Antibiotic resistance, tolerance to toxic metals, production of toxins, and the synthesis of enzymes. Used for gene manipulation in biotechnology Inclusions reserve deposits. Cells accumulate certain nutrients and use them when the environment is deficient. Metachromatic Granules: -Volutin, characteristic of Corynebacterium diphtheriae.-Stain red with certain blue dyes such as methylene blue. Polysaccharide Granules: Glycogen and starch, presence can be demonstrated using Iodine. Sulfur Granules: Derive energy by oxidizing sulfur. Thiobacillus (sulfur bacteria) Magnetosomes: Iron oxide (Fe3O4). Decompose hydrogen peroxide& Movement. Lipid Inclusions. Carboxysomes: Ribulose 1,5-diphosphate E.g. bacillus megaterium carboxylase. Gas Vacuoles.  Endospores Resting structures(highly durable dehydrated cells with thick walls and additional layers.) formed by some bacteria. Sporulation: endospore formation. Endospores do NOT carry out metabolic reactions. - Endospores contains a large amount of an organicacid called dipicolinic acid (DPA: protects the endospore DNAagainst damage. - Endospores could be Terminal, Subterminal, or Central. - Germination: endospore returning to its vegetative state. - Thick layers of peptidoglycan are laid down between the two membrane layers. Endospore formation stages  Three sources of energy in bacteria There are three types of bacteria which are classified on the basis of the nutritional requirements. There are photoautotrophs which can perform the process of carbon dioxide fixation and the source of energy is sunlight. The chemoautotrophs are the organisms which can use carbon dioxide as the source of carbon and inorganic compounds like ammonia and H2S. The chemoheterotrophs can use the energy and carbon from the organic compounds.  Photoautotrophs Photoautotrophs are organisms that can make their own energy using light and carbon dioxide via the process of photosynthesis. The word photoautotroph is a combination of autotroph, the word for an organism that makes its own food, and the prefix photo-, which means “light”. Green plants and photosynthetic bacteria are examples of photoautotrophs. They are not to be confused with photoheterotrophs, which also make energy from light but cannot use carbon dioxide as their sole source of carbon, and instead use organic materials.  Chemoautotrophic bacteria Chemoautotrophic bacteria get their energy from oxidizing inorganic compounds. In other words, instead of using the energy of photons from the sun, they break the chemical bonds of substances that don’t contain carbon in order to get their energy. Some of the inorganic chemicals chemoautotrophic bacteria use are hydrogen sulfide, ammonia and iron. For example, the sulfur-eating bacteria Thiothrix oxidizes hydrogen sulfide to produce water and sulfur. The energy that is stored in the chemical bonds of the hydrogen sulfide molecule is released during the reaction. The bacteria use this energy along with carbon dioxide to make sugars and carbohydrates. Chemoautotrophic bacteria often live in extreme environments like deep sea vents in the ocean, hence their other name, extremophiles.  Chemoheterotrophs Chemoheterotrophs are organisms that get their energy source and carbon source from organic sources. Chemoheterotrophs must consume organic building blocks that they are unable to make themselves. Most get their energy from organic molecules such as  Enzymes of microorganisms Microbial enzymes are known to be superior enzymes obtained from different microorganisms, particularly for applications in industries on commercial scales.... Various established classes of enzymes are specific to perform specialized catalytic reactions and have established their uses in selected bio-processes. Reaction pathway  Enzyme structure  Enzymes are proteins  They have a globular shape  A complex 3-D structure  The active site  One part of an enzyme, the active site, is particularly important  The shape and the chemical environment inside the active site permits a chemical reaction to proceed more easily © H.PELLETIER, M.R.SAWAYA ProNuC Database  Cofactors Nitrogenase - click for Jmol version  An additional non- protein molecule that is needed by some enzymes to help the reaction  Tightly bound cofactors are called prosthetic groups  Cofactors that are bound and released easily are called coenzymes  Many vitamins are coenzymes Nitrogenase enzyme with Fe, Mo and ADP cofactors Jmol from a RCSB PDB file © 2007 Steve Cook H.SCHINDELIN, C.KISKER, J.L.SCHLESSMAN, J.B.HOWARD, D.C.REES STRUCTURE OF ADP X ALF4(-)-STABILIZED NITROGENASE COMPLEX AND ITS IMPLICATIONS FOR SIGNAL TRANSDUCTION; NATURE 387:370 (1997) The substrate The substrate of an enzyme are the reactants that are activated by the enzyme Enzymes are specific to their substrates The specificity is determined by the active site The Lock and Key Hypothesis  Fit between the substrate and the active site of the enzyme is exact  Like a key fits into a lock very precisely  The key is analogous to the enzyme and the substrate analogous to the lock.  Temporary structure called the enzyme-substrate complex formed  Products have a different shape from the substrate  Once formed, they are released from the active site  Leaving it free to become attached to another substrate The Lock and Key Hypothesis S E E E Enzyme- Enzyme may substrate be used again complex P P Reaction coordinate  The Lock and Key Hypothesis  This explains enzyme specificity  This explains the loss of activity when enzymes denature  The Induced Fit Hypothesis  Some proteins can change their shape (conformation)  When a substrate combines with an enzyme, it induces a change in the enzyme’s conformation  The active site is then moulded into a precise conformation  Making the chemical environment suitable for the reaction  The bonds of the substrate are stretched to make the reaction easier (lowers activation energy) The Induced Fit Hypothesis Hexokinase (a) without (b) with glucose substrate http://www.biochem.arizona.edu/classes/bioc462/462a/NOTES/ENZYMES/enzyme_mechanism.html  This explains the enzymes that can react with a range of substrates of similar types  Factors affecting Enzymes  substrate concentration  pH  temperature  inhibitors Substrate concentration: Non-enzymic reactions Reaction velocity Substrate concentration The increase in velocity is proportional to the  substrate concentration Substrate concentration: Enzymic reactions Vmax Reaction velocity Substrate concentration Faster reaction but it reaches a saturation point when all the  enzyme molecules are occupied. If you alter the concentration of the enzyme then Vmax will  change too. The effect of pH Optimum pH values Enzyme activity Trypsin Pepsin 1 3 5 7 9 11 pH The effect of pH  Extreme pH levels will produce denaturation  The structure of the enzyme is changed  The active site is distorted and the substrate molecules will no longer fit in it  At pH values slightly different from the enzyme’s optimum value, small changes in the charges of the enzyme and it’s substrate molecules will occur  This change in ionisation will affect the binding of the substrate with the active site. The effect of temperature  At high temperatures proteins denature  The optimum temperature for an enzyme is the temperature at which maximum activity of enzyme is achieved  The minimum temperature is the temperature below which the enzyme activity is not detected  The maximum temperature is the temperature above which the enzyme activity is not detected because enzyme is protein in nature and high temperature may denaturate enzyme. Thank you