BIOL 3340 Chapter 3

Microbial Cell Structure

Types of Cells Two major classes: eukaryotes & prokaryotes. Differences: the materials making up the nucleus of eukaryotic cells are separated from the rest of the cell by the nuclear membrane, whereas in prokaryotic cells these materials are not separated. All animals and plant cells are eukaryotic including fungi. Bacteria, cyanobacteria and the mycoplasmas are prokaryotic.

Size, Shape, and Arrangement of Bacterial cells Cocci (s., coccus) – spheres diplococci (s., diplococcus) – pairs streptococci – chains staphylococci – grape-like clusters tetrads – 4 cocci in a square sarcinae – cubic configuration of 8 cocci

……Size, Shape, and Arrangement Bacilli (s., bacillus): – rods coccobacilli – very short rods vibrios – resemble rods, comma shaped spirilla (s., spirillum) – rigid helices spirochetes – flexible helices mycelium – network of long, multinucleate filaments Check on line lab Manual for Bacterial shapes)

……Size, Shape, and Arrangement Sizes: Typically ~  m (with some exceptions) Typical coccus: ~ 1  m (e.g. Staphylococcus)Staphylococcus Typical short rod: ~ 1 x 5  m (e.g. E. coli)E. coli Barely within the best resolution of a good compound light microscopecompound light microscope

Bacterial Shapes

Cell Structure of Procaryotes Prokaryotic cells The constituents of a typical bacterium are as follows: Bacterial Cell Wall and Capsule – bacteria are surrounded by a cell wall, which not only contains polysaccharide but also contains protein and lipid. In some bacteria, the cell wall is surrounded by the capsule. The cell wall and capsule provide shape and form to the bacterium and also acts as a physical barrier between the bacterium and its environment. Nucleoids – in bacteria the nuclear material is concentrated in a region called the nucleoid within the cytoplasm.

A typical Bacterial Cell

….Cell Structure There is no membrane-bound nucleus in prokaryotes. Instead the DNA is located within a specialized region of the cytoplasm of the cell called the nucleoid region. There is no nuclear membrane surrounding the nucleoid. Bacterial flagella – many bacteria possess one or more flagella for locomotion.

Gram-negative Cell Walls and Acid Fast Fast cell wall in Chapter 3

Procaryotic Cell Membranes Cell Membranes: membranes are an absolute requirement for all living organisms. plasma membrane encompasses the cytoplasm some procaryotes also have internal membrane systems

Functions of the Plasma Membrane separation of cell from its environment selectively permeable barrier some molecules are allowed to pass into or out of the cell transport systems aid in movement of molecules detection of and response to chemicals in surroundings with the aid of special receptor molecules in the membrane

Fluid Mosaic Model of Membrane Structure

…..Plasma membrane

…Phospholipid layer polar ends interact with water hydrophillic nonpolar ends insoluble in water hydrophobic

Membrane Proteins Peripheral proteins: loosely associated with the membrane and easily removed Integral proteins embedded within the membrane and not easily removed

Procaryotic Cytoplasm Cytoplamic Matrix: Cytoplasm contains the nucleoid, ribosomes and inclusion bodies lacks organelles bound by unit membranes composed largely of water is a major part of the protoplasm (the plasma membrane and everything within)

..Cytoplasmic Matrix Viscous aqueous suspension of proteins, nucleic acid, dissolved organic compounds, mineral salts Network of protein fibers similar to the eukaryotic cytoskeleton. Cytoplasmic Inclusion Bodies: granules of organic or inorganic material that are stockpiled by the cell for future use. some are enclosed by a single-layered membrane

….Cytoplasmic inclusions Cytoplasmic inclusions: Glycogen Granules Glycogen Poly-  -hydroxybutyrate granules Poly-  -hydroxybutyrate granules Lipid droplets Gas vacuoles Metachromatic granules (Phosphate crystals or volutin granules) Metachromatic granules Sulfur Granules

Ribosomes Ribosomes: complex structures consisting of protein and RNA sites of protein synthesis smaller than eucaryotic ribosomes procaryotic ribosomes  70S eucaryotic ribosomes  80S

The Nucleoid Nucleoid: irregularly shaped region location of chromosome usually 1/cell not membrane-bound

The Procaryotic Chromosome The Chromosomes: usually a closed circular, double-stranded DNA molecule looped and coiled extensively

Plasmids Plasmids: usually small, closed circular DNA molecules exist and replicate independently of chromosome have relatively few genes present

Procaryotic Cell Walls Prokaryotic Cell Wall: rigid structure that lies just outside the plasma membrane (detail to continue)

Functions of Cell Wall provides characteristic shape to cell protects the cell from osmotic lysis may also contribute to pathogenicity very few procaryotes lack cell walls

Cell Walls of Bacteria Gram Staining developed by Gram in 1888: bacteria are divided into two major groups based on the response to gram-stain procedure gram-positive bacteria stain purple gram-negative bacteria stain pink staining reaction due to cell wall structure

Gram Positive and Gram negative

Gram-Positive Cell Walls Gram positive bacteria composed primarily of peptidoglycan Gram positive bacteria composed primarily of peptidoglycan Peptidoglycan are polymers which contains N-acetylglucosamine and N- acetylmuramic acid and several different amino acids Peptidoglycan are polymers which contains N-acetylglucosamine and N- acetylmuramic acid and several different amino acids Walls contain teichoic acid ( polymers of glycerol or ribitol joined by phosphate groups) Walls contain teichoic acid ( polymers of glycerol or ribitol joined by phosphate groups)

..Gram-Positive Cell Walls The periplasmic space lies between plasma membrane and cell wall and is smaller than that of gram-negative bacteria The periplasmic space lies between plasma membrane and cell wall and is smaller than that of gram-negative bacteria periplasm has relatively few proteins periplasm has relatively few proteins enzymes secreted by gram-positive bacteria are called exoenzymes enzymes secreted by gram-positive bacteria are called exoenzymes

Gram-Negative Cell Walls consist of a thin layer of peptidoglycan surrounded by an outer membrane consist of a thin layer of peptidoglycan surrounded by an outer membrane outer membrane composed of lipids, lipoproteins, and lipopolysaccharide (LPS) outer membrane composed of lipids, lipoproteins, and lipopolysaccharide (LPS) no teichoic acids no teichoic acids

…..Gram Negative more complex than gram-positive walls more complex than gram-positive walls periplasmic space differs from that in gram-positive cells periplasmic space differs from that in gram-positive cells may constitute 20-40% of cell volume may constitute 20-40% of cell volume many enzymes present in periplasm many enzymes present in periplasm

Gram Positive and Negative cell Wall

Assignments Features of a prokaryotic cell Features of a prokaryotic cell List the differences between a gram positive and gram negative cell wall. List the differences between a gram positive and gram negative cell wall.

Variations on Cell Wall Architecture Acid-fast Cell WallsAcid-fast Cell Walls: Acid-fast Cell Walls Many genera in the “High GC gram-positive” bacterial group contain mycolic acids, embedded in the peptidoglycan. Many genera in the “High GC gram-positive” bacterial group contain mycolic acids, embedded in the peptidoglycan.mycolic acidsmycolic acids Mycolic acids are a class of waxy, extremely hydrophobic lipids. Mycolic acids are a class of waxy, extremely hydrophobic lipids. Certain genera contain very large amounts of this lipid, and are difficult to gram stain. Certain genera contain very large amounts of this lipid, and are difficult to gram stain. These genera may be identified by the “acid- fast” staining technique. These genera may be identified by the “acid- fast” staining technique.“acid- fast” staining technique“acid- fast” staining technique Includes Mycobacterium and Nocardia. Includes Mycobacterium and Nocardia.MycobacteriumNocardiaMycobacteriumNocardia

..Variations on Cell Wall Architecture MycoplasmasMycoplasmas: Mycoplasmas Bacteria that are naturally have no cell walls Bacteria that are naturally have no cell walls Bacteria Includes Mycoplasma and Ureaplasma Includes Mycoplasma and Ureaplasma ArchaeaArchaea : Archaea Have archaea cell walls with no peptidoglycan Have archaea cell walls with no peptidoglycanarchaea cell walls archaea cell walls Many have cell walls containing pseudomurein, a polysaccharide similar to peptidoglycan but containing N- acetylglucosamine and N- acetyltalosaminuronic acid. Many have cell walls containing pseudomurein, a polysaccharide similar to peptidoglycan but containing N- acetylglucosamine and N- acetyltalosaminuronic acid.

Capsules, Slime Layers, and S-Layers Layers of material lying outside the cell wall capsules capsules usually composed of polysaccharides usually composed of polysaccharides well organized and not easily removed from cell well organized and not easily removed from cell slime layers slime layers similar to capsules except diffuse, unorganized and easily removed. similar to capsules except diffuse, unorganized and easily removed. a capsule or slime layer composed of polysaccharides can also be referred to as a glycocalyx a capsule or slime layer composed of polysaccharides can also be referred to as a glycocalyx

Glycocalyx

S-layers: S-layers: regularly structured layers of protein or glycoprotein. regularly structured layers of protein or glycoprotein. in bacteria the S-layer is external to the cell wall. in bacteria the S-layer is external to the cell wall. Regular “floor tile” pattern. Regular “floor tile” pattern. Regular “floor tile” pattern Regular “floor tile” pattern Function not clear -- Stability? Function not clear -- Stability?

Functions of Capsules, Slime Layers, and S-layers protection from host defenses (e.g., phagocytosis) protection from host defenses (e.g., phagocytosis) protection from harsh environmental conditions (e.g., desiccation), chemicals or osmotic stress protection from harsh environmental conditions (e.g., desiccation), chemicals or osmotic stress attachment to surfaces attachment to surfaces facilitate motility facilitate motility nutrient Storage nutrient Storage

Pili and Fimbriae Fimbriae (s., fimbria) short, thin, hairlike, proteinaceous appendages up to 1,000/cell short, thin, hairlike, proteinaceous appendages up to 1,000/cell mediate attachment to surfaces mediate attachment to surfaces sex pili (s., pilus): similar to fimbriae except longer, thicker, and less numerous (1-10/cell) similar to fimbriae except longer, thicker, and less numerous (1-10/cell) required for mating required for mating

Fimbriae

…Fimbriae Function s: Mobility Mobility Almost all motile bacteria are motile by means of flagella Almost all motile bacteria are motile by means of flagellabacteria Motile vs. non motile bacteria. Motile vs. non motile bacteria. Different species have different flagella arrangements Different species have different flagella arrangementsflagella arrangementsflagella arrangements Structure: Structure: Filament composed of the protein flagellin Filament composed of the protein flagellin Hook & Rotor Assembly & Permits rotational "spinning" movement Hook & Rotor Assembly & Permits rotational "spinning" movement

…Fimbriae

Chemotaxis movement towards a chemical attractant or away from a chemical repellent movement towards a chemical attractant or away from a chemical repellent concentrations of chemical attractants and chemical repellents detected by chemoreceptors on surfaces of cells concentrations of chemical attractants and chemical repellents detected by chemoreceptors on surfaces of cells

Bacterial Endospores Bacterial Spores are formed by some bacteria as dormant structures. are formed by some bacteria as dormant structures. resistant to numerous environmental conditions e.g heat, radiation,chemicals, nutrient depletion, resistant to numerous environmental conditions e.g heat, radiation,chemicals, nutrient depletion, desiccation, and waste buildup. desiccation, and waste buildup. Bacterial spores are NOT a reproductive structure, like plant or fungal spores. Bacterial spores are NOT a reproductive structure, like plant or fungal spores. Produced by very few genera of bacteria Produced by very few genera of bacteriabacteria Major examples Bacillus & Clostridium Major examples Bacillus & ClostridiumBacillusClostridiumBacillusClostridium

…endospores Sporogenesis

Sporogenesis Sporogenesis: Also called endospore formation or sporulation Also called endospore formation or sporulation normally commences when growth ceases because of lack of nutrients normally commences when growth ceases because of lack of nutrients A copy of the bacterial chromosome is surrounded by a thick, durable spore coat. A copy of the bacterial chromosome is surrounded by a thick, durable spore coat. When the vegetative cell dies and ruptures, the free spore is released. When the vegetative cell dies and ruptures, the free spore is released. When spore encounters favorable growth conditions, spore coat ruptures and a new vegetative cell is formed. When spore encounters favorable growth conditions, spore coat ruptures and a new vegetative cell is formed.

..Sporogenesis Complex multistage process

Spore Germination

Bibliography d d d d o3340/home.html o3340/home.html o3340/home.html o3340/home.html Lecture PowerPoints Prescott’s Principles of Microbiology-Mc Graw Hill Co. Lecture PowerPoints Prescott’s Principles of Microbiology-Mc Graw Hill Co. biology.suite101.com/article.cfm/cell_structure biology.suite101.com/article.cfm/cell_structure biology.suite101.com/article.cfm/cell_structure biology.suite101.com/article.cfm/cell_structure n5_2.htm n5_2.htm n5_2.htm n5_2.htm