Module 2 - Bacterial Anatomy (for Students).pdf

2Microbial Cell Structure and Function Lecture Presentations by Florabelle Querubin De La Salle University © 2021 Pearson Education, Ltd.  Chapter 2 Contents I. The Cell Envelope II. Cell Surface Structures and Inclusions III. Cell Locomotion IV. Eukaryotic Microbial Cells (r...

2Microbial Cell Structure and Function Lecture Presentations by Florabelle Querubin De La Salle University © 2021 Pearson Education, Ltd.  Chapter 2 Contents I. The Cell Envelope II. Cell Surface Structures and Inclusions III. Cell Locomotion IV. Eukaryotic Microbial Cells (reading assignment) © 2021 Pearson Education, Ltd.  I. The Cell Envelope The cell envelope consists of a series of layered structures that surround the cytoplasm and govern cellular interactions with the external environment. (1) It governs transport of nutrients into the cell and wastes out of the cell (2) It is the site of energy conservation (3) It governs cell shape (4) It protects the cell from mechanical stress (5) It can help the cell attach to surfaces and even protect the cell from attack © 2021 Pearson Education, Ltd.  2.1 The Cytoplasmic Membrane The cytoplasmic membrane surrounds the cytoplasm—the mixture of macromolecules and small molecules inside the cell—and separates it from the environment. The cytoplasmic membrane is physically rather weak but is an ideal structure for its major cellular function: selective permeability. © 2021 Pearson Education, Ltd.  2.1 The Cytoplasmic Membrane Bacterial Cytoplasmic Membranes functional group / choline © 2021 Pearson Education, Ltd.  2.1 The Cytoplasmic Membrane Bacterial Cytoplasmic Membranes Transmembrane proteins integral membrane proteins that extend completely across the membrane embedded proteins loosely attached proteins © 2021 Pearson Education, Ltd.  2.1 The Cytoplasmic Membrane Archaeal Cytoplasmic Membranes The polar head fatty acids in Bacteria and Eukarya groups in archaeal lipids can be sugars, ethanolamine, or a variety of other molecules. © 2021 Pearson Education, Ltd.  2.1 The Cytoplasmic Membrane Cytoplasmic Membrane Function © 2021 Pearson Education, Ltd.  2.1 The Cytoplasmic Membrane Cytoplasmic Membrane Function Transport proteins - not simply ferrying proteins but instead function to accumulate solutes against the concentration gradient. Transport proteins typically display high sensitivity and high specificity. Low- affinity transporter when the nutrient is present at high external concentration High-affinity transporter when the nutrient is present at low concentration © 2021 Pearson Education, Ltd.  2.2 Transporting Nutrients into the Cell cells accumulate solutes against the Active Transport and Transporters concentration gradient. extremely high substrate affinity (1) the transported substance is chemically modified during the transport process, and (2) an energy-rich organic compound (rather than the proton motive force) drives the transport event. ATP- binding cassette three components: a binding solute and a proton are solute and a proton are protein, a transmembrane transported in opposite cotransported in the protein channel, and an ATP- directions same direction hydrolyzing protein © 2021 Pearson Education, Ltd. Bacteria vs Archaeal Membrane Bacteria Archaea Lipid bilayer Lipid monolayer Ester-linked lipids Ether-linked lipids Straight chain fatty Branched fatty acids acids  2.3 The Cell Wall To withstand this turgor pressure – that can cause cell lysis –, the cell envelopes of most Bacteria and Archaea have a layer outside the cytoplasmic membrane called the cell wall. Besides protecting against osmotic lysis, cell walls also maintain cell shape and rigidity. © 2021 Pearson Education, Ltd.  2.3 The Cell Wall © 2021 Pearson Education, Ltd.  2.3 The Cell Wall Bacterial Cell Walls The cell walls found in Bacteria contain a rigid polysaccharide called peptidoglycan (PG) that confers structural strength on the cell. Note: PG is unique to Bacteria and is not found in Archaea or Eukarya. Amino acid composition vary considerably between bacterial species © 2021 Pearson Education, Ltd.  2.3 The Cell Wall Bacterial Cell Walls Strands of peptidoglycan run parallel to each other around the circumference of the cell In gram-positive bacteria, peptide cross-links often contain a short peptide “interbridge” – vary confer strength around the circumference of the cell between species 2-3 layers in gram-negative bacteria (2-7 nm thick) can be 15 or more layers thick in gram-positive bacteria (20-35 nm) © 2021 Pearson Education, Ltd.  2.3 The Cell Wall Bacterial Cell Walls Source: OpenStax and the American Society for Microbiology Press. Microbiology.  2.3 The Cell Wall Bacterial Cell Walls Teichoic acids in gram-positive bacteria composed of glycerol phosphate or ribitol phosphate with attached molecules of glucose or d-alanine (or both). covalently linked to PG covalently bonded to membrane lipids – lipoteichoic acids contribute to structural integrity, regulation of cell growth, cation binding, virulence, antimicrobial resistance, and biofilm formation (Schneewind and Missiakas, 2017) © 2021 Pearson Education, Ltd.  2.3 The Cell Wall Bacterial Cell Walls Peptidoglycan can be destroyed by lysozyme (present in human secretions), an enzyme that cleaves the glycosidic bond between N- acetylglucosamine and N-acetylmuramic acid Many antibiotics, including penicillin, also target peptidoglycan Whereas lysozyme destroys preexisting peptidoglycan, penicillin blocks the formation of peptide cross-links, which compromises the strength of the peptidoglycan, leading to cell lysis. © 2021 Pearson Education, Ltd.  2.3 The Cell Wall Archaeal Cell Walls Archaea lack peptidoglycan and typically lack an outer membrane immune from Gram stain reaction is not very destruction useful for predicting the structures by both lysozyme and of archaeal cell envelopes penicillin Most Archaea lack a polysaccharide- containing cell wall and instead have an S-layer, which is a rigid protein shell that functions to prevent osmotic lysis just as does the bacterial cell wall Methane-producing Archaea (methanogens) contain a polysaccharide called pseudomurein, which is structurally remarkably similar to peptidoglycan (the term murein is from the Latin word for “wall” and was an old term for peptidoglycan) © 2021 Pearson Education, Ltd.  2.4 LPS: The Outer Membrane spans the gap between the LPS layer and the peptidoglycan layer Major differences of OM from CM: presence of polysaccharide molecules covalently bound to lipids presence of porins – transmembrane proteins that allow nonspecific transport of solutes © 2021 Pearson Education, Ltd.  2.4 LPS: The Outer Membrane LPS functions: facilitate surface recognition virulence factors for some bacterial pathogens contribute to the mechanical strength of the cell © 2021 Pearson Education, Ltd.  2.4 LPS: The Outer Membrane Structure and Activity of LPS Ionic bonds to divalent cations (such as Ca2+ and Mg2+) between adjacent LPS – provides strength to the OM Lipid A – fatty acids are bonded through the amine groups from a disaccharide composed of glucosamine phosphate toxicity – endotoxin  produced by Salmonella and enteropathogenic strains of Escherichia coli transmitted in contaminated foods are classic examples © 2021 Pearson Education, Ltd.  2.4 LPS: The Outer Membrane The Periplasm and Porins These extracellular proteins reside in the periplasm, a space of about 15 nm located between the outer surface of the cytoplasmic membrane and the inner surface of the outer membrane. hydrolytic enzymes – initial degradation of polymeric substances binding proteins – begin the process of transporting substrates chemoreceptors – govern the chemotaxis response proteins that construct extracellular structures (such as peptidoglycan and the outer membrane) from precursor molecules secreted through the cytoplasmic membrane © 2021 Pearson Education, Ltd.  2.4 LPS: The Outer Membrane The Periplasm and Porins The outer membrane is relatively permeable to small molecules because of proteins called porins that function as channels for the entrance and exit of solutes. Nonspecific porins form water-filled channels for very small hydrophilic substances Specific porins contain a binding site for one or a group of structurally related substances © 2021 Pearson Education, Ltd.  Antibiotics and their target OpenStax and the American Society for Microbiology Press. Microbiology.  The Cell Wall of other Bacteria Mycoplasmas Absence of cell wall Sterol and lipoglycans in the cytoplasmic membrane Mycoplasma mycoides. Metal-shadowed transmission electron micrograph. © 2021 Pearson Education, Ltd.  2.5 Diversity of Cell Envelope Structure S-Layers found in many Bacteria (5-20 nm) and in nearly all Archaea (70 nm) consists of a paracrystalline monolayer of interlocking molecules of protein or glycoprotein always the outermost layer of the cell envelope © 2021 Pearson Education, Ltd.  2.5 Diversity of Cell Envelope Structure S-Layers Functions: Archaea – can take the role of the cell wall and are responsible for providing structural strength, protecting the cell from osmotic lysis, and conferring cell shape can also facilitate cell surface interactions, such as attachment increase the ability of some bacterial pathogens to cause disease by either promoting adhesion or protecting the cell from host defenses © 2021 Pearson Education, Ltd.  2.5 Diversity of Cell Envelope Structure Alternative Configurations of the Cell Envelope classic gram-negative type gram-negative envelope and typical archaeal cell envelope pathogenic bacterium whose cell bacterial cell envelope an S-layer envelope consists of only a CM many Archaea have only an S-layer outside of their cytoplasmic membrane methanogenic Archaea also have cell walls made of pseudomurein that may or may not have an outer S-layer heat-loving Ignococcus, an Archaea, have an outer membrane composed largely of archaeal isoprenoid lipids and lacks LPS Mycoplasmas – contain sterols in their cytoplasmic membranes to add strength and rigidity; little osmotic pressure when living within the cytoplasm of another cell © 2021 Pearson Education, Ltd.  II. Cell Surface Structures and Inclusions © 2021 Pearson Education, Ltd.  2.6 Cell Surface Structures Capsules and Slime Layers A sticky coat of polysaccharide formed outside of the cell envelope Capsule – polysaccharide is organized in a tight matrix that excludes small particles and is tightly attached to the cell Slime layer – polysaccharide is loosely attached; it will not exclude particles and is more difficult to see microscopically © 2021 Pearson Education, Ltd.  2.6 Cell Surface Structures Capsules and Slime Layers Functions: attachment of microorganisms to solid surfaces – can form biofilm contributing to the infectivity of a bacterial pathogen and preventing dehydration (bacterial outer surface layers bind water) © 2021 Pearson Education, Ltd.  2.6 Cell Surface Structures Fimbriae, Pili, and Hami Pili are thin (2–10 nm in diameter) filamentous structures made of protein that extend from the surface of a cell and can have many functions Short pili that mediate attachment are often called fimbriae Functions: conjugative pili – conjugation electrically conductive pili – nanowires type IV pili – twitching motility © 2021 Pearson Education, Ltd.  2.6 Cell Surface Structures Fimbriae, Pili, and Hami SM1 group of Archaea resembles a tiny grappling hook resemble type IV pili except for their barbed terminus, which functions to attach cells both to surfaces and to each other © 2021 Pearson Education, Ltd.  2.7 Cell Inclusions Carbon Storage Polymers Poly-β-hydroxybutyric acid (PHB) (C4) Polymer can vary in length from as short as C3 to as long as C18 carbon- and energy- storage polymers synthesized by cells when there is an excess of carbon Glycogen polymer of glucose carbon and energy and is produced when carbon is in excess © 2021 Pearson Education, Ltd.  2.7 Cell Inclusions Polyphosphate, Sulfur, and Carbonate Minerals Polyphosphate inorganic phosphate (PO43-) source of phosphate for nucleic acid and phospholipid biosynthesis when phosphate is limiting can be broken down to synthesize the energy-rich compound ATP from ADP Sulfur granules (elemental sulfur, S0, from oxidation of sulfide) oxidize reduced sulfur compounds, such as hydrogen sulfide (H2S) generates electrons for use in energy metabolism or CO 2 fixation © 2021 Pearson Education, Ltd.  2.7 Cell Inclusions Polyphosphate, Sulfur, and Carbonate Minerals unicellular cyanobacterium Gloeomargarita forms intracellular granules of benstonite, a carbonate mineral that contains barium, strontium, and magnesium might function as ballast to maintain cells of this cyanobacterium in their habitat could be a way to sequester carbonate (a source of CO 2) to support autotrophic growth Biomineralization microbiological process of forming minerals © 2021 Pearson Education, Ltd.  2.7 Cell Inclusions Gas Vesicles structures that confer buoyancy and allow the cells to position themselves in regions of the water column that best suit their metabolisms Blooms – cyanobacteria that form massive accumulations; on or near the lake surface where sunlight is most intense, and photosynthesis can occur at maximal rates impermeable to water and solutes but permeable to gases Gas vacuoles – cluster of vesicles © 2021 Pearson Education, Ltd.  2.7 Cell Inclusions Magnetosomes bacteria can orient themselves within a magnetic field biomineralized particles of the magnetic iron oxides magnetite [Fe(II)Fe(III)2O4] or greigite [Fe(II)Fe(III)2S4] Magnetotaxis – the process of migrating along Earth’s magnetic field lines © 2021 Pearson Education, Ltd.  2.8 Endospores highly differentiated dormant cells that function as survival structures and can tolerate harsh environmental conditions, including extreme heat, radiation, chemical exposure, drying, and nutrient depletion Endospores are not reproductive structures, such as the spores of fungi, but are rather the dormant stage of a bacterial life cycle: vegetative cell  endospore  vegetative cell © 2021 Pearson Education, Ltd.  2.8 Endospores Endospore Formation and Germination Sporulation – process of cellular differentiation that results in endospore formation (a) a highly refractile free endospore. (b) Activation : The spore becomes less refractile as the spore is hydrated. (c) Germination : the spore begins to develop into a vegetative cell. (d) Outgrowth : the vegetative cell emerges and begins to divide. © 2021 Pearson Education, Ltd.  2.8 Endospores Endospore Structure and Features © 2021 Pearson Education, Ltd.  2.8 Endospores Endospore Structure and Features Core – contains DNA and ribosomes and develops from the cytoplasm Inner membrane – from the cytoplasmic membrane Cortex – composed of peptidoglycan Outer membrane – special membrane formed during sporulation Endospore coat – composed of layers of spore-specific proteins Exosporium – outer proteinaceous layer © 2021 Pearson Education, Ltd.  2.8 Endospores Endospore Structure and Features Calcium-dipicolinic acid complex forms about 10% of the dry weight of the endospore  bind water (dehydrate endospore) inserts between bases in DNA  stabilize DNA against heat denaturation Small acid-soluble spore proteins (SASPs) bind tightly to DNA in the core and protect it from potential damage from ultraviolet radiation, desiccation, and dry heat alter the physical structure of DNA, causing it to become more compact carbon and energy source for the outgrowth of a new vegetative cell from the endospore during germination © 2021 Pearson Education, Ltd.  2.8 Endospores The Sporulation Cycle © 2021 Pearson Education, Ltd.  Plasmid circular dsDNA that can exist and replicate independently of the chromosome or may be integrated with it not required for growth and reproduction carry genes w/c confer selective advantages ✓ drug resistance ✓ pathogenicity ✓ new metabolic activities https://www.genome.gov/genetics-glossary/Plasmid Prokaryote vs Eukaryote Bacteria Archaea  III. Cell Locomotion © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility Bacteria are motile by swimming due to a structure called the flagellum (plural, flagella); an analogous structure called the archaellum is present in many Archaea. tiny rotating machines that function to push or pull the cell through a liquid Bacterial flagella are long, thin appendages (15–20 nm wide, depending on the species) free at one end and anchored into the cell at the other end. © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility Flagella and Flagellation Polar flagellation, the flagella are attached at one or both ends of a cell A group of many flagella (called a tuft) may arise at one end of the cell, a type of polar flagellation called Bacteria flagella types, illustration - Stock Image F035/5695. (2023, August 31). Science Photo Library. lophotrichous https://www.sciencephoto.com/media/1244673/view/bacteria-flagella-types-illustration When a tuft of flagella emerges from both poles of the cell, flagellation is called amphitrichous. In peritrichous flagellation, flagella are inserted around the cell surface. © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility Flagella and Flagellation move slowly in a straight move more rapidly and line, stop and then head off continuously, and some are in a new direction able to reverse their direction © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility Flagella Structure and Activity The main part of the flagellum, called the filament, is composed of many copies of a protein called flagellin. A wider region at the base of the filament called the hook consists of a single type of protein and connects the filament to the flagellum motor in the basal body. © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility Flagellum motor: rotor In gram-negative bacteria: An outer ring, called the L ring, is anchored in the outer membrane A second ring, called the P ring, is anchored in the peptidoglycan layer. A third set of rings, called the MS and C rings, are located within the cytoplasmic membrane and the cytoplasm, respectively. In gram-positive bacteria, which lack an outer membrane, only the inner pair of rings is present. © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility Flagellum motor: stator Surrounding the inner rings and anchored in the cytoplasmic membrane and the peptidoglycan is the stator, which is composed of Mot proteins. On the cytoplasmic side of the MS ring is the export apparatus, a type III secretion system that facilitates synthesis of the flagellum. © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility Flagella Structure and Activity Rotation of the flagellum occurs at the expense of the proton motive force. About 1200 protons are translocated by each rotation of the flagellum. © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility A flagellar filament Flagellar Synthesis grows not from its (1) The MS ring is synthesized first and inserted into base the cytoplasmic membrane. Approximately 20,000 (2) Then other anchoring proteins are synthesized along with the hook and the cap before the flagellin protein filament forms. molecules are needed to make one filament. (3) Flagellin molecules synthesized in the cytoplasm are exported through the export apparatus present on the cytoplasmic side of the basal body. (4) Cap proteins assist flagellin molecules to assemble in the proper fashion at the flagellum tip © 2021 Pearson Education, Ltd.  2.9 Flagella, Archaella, and Swimming Motility Archaella proteins are unrelated to those of flagella, and in evolutionary terms are more closely related to type IV pili smaller than flagella, measuring about 10–13 nm in width not hollow and are assembled from their bases driven by ATP hydrolysis Archaea swim much more slowly than Bacteria © 2021 Pearson Education, Ltd.  2.10 Surface Motility Surface motility results in distinctive colony morphology because cells can move out and away from the center of the colony Gliding bacteria (a, b) The large filamentous cyanobacterium Oscillatoria (b) Oscillatoria filaments gliding on an agar surface (c) Masses of the bacterium Flavobacterium johnsoniae gliding away from the center of the colony (d) Nongliding mutant strain of F. johnsoniae © 2021 Pearson Education, Ltd.  2.10 Surface Motility Twitching Motility requires type IV pili, which extend from one pole of the cell, attach to a surface, and then retract to pull the cell forward energy comes from ATP hydrolysis gram-negative bacterium Pseudomonas  biofilm formation Myxobacteria: social motility, which is caused by twitching, and adventurous motility, which is caused by gliding Movement in groups is facilitated by type IV pili and the secretion of extracellular polysaccharides © 2021 Pearson Education, Ltd.  2.10 Surface Motility Gliding Motility smooth motion along the long axis of a cell without the aid of external propulsive structures; a continuous movement Gliding bacteria are typically filamentous or rod-shaped helical intracellular track made of proteins that run in a continuous loop around the cell “gliding motors,” rotary motors that are driven by the proton motive force; similar to flagellar motor adhesion proteins that grab onto surfaces on the outside of the cell © 2021 Pearson Education, Ltd.  2.11 Chemotaxis Chemotaxis – a response to chemicals; Gliding bacteria Phototaxis – a response to light; filamentous cyanobacteria © 2021 Pearson Education, Ltd.  2.11 Chemotaxis Chemotaxis in Peritrichously Flagellated Bacteria cell moves about its environment in random fashion through a series of runs and tumbles During chemotaxis cells will tend to move toward the attractant over time, but cells do not move continuously nor directly toward the attractant; instead, they exhibit a behavior flagellar motor rotates known as a biased random clockwise walk. flagellar motor rotates counterclockwise © 2021 Pearson Education, Ltd.  2.11 Chemotaxis Chemotaxis in Peritrichously Flagellated Bacteria Cells sample the concentration of attractant not over space, but rather over time If the concentration goes up, runs become longer and tumbles less frequent, but if the concentration goes down, runs become shorter and tumbles more frequent. © 2021 Pearson Education, Ltd.  2.11 Chemotaxis Chemotaxis in Peritrichously Flagellated Bacteria For a repellent, the same mechanism applies, but the response is reversed, with longer runs triggered by a decrease in concentration of the repellent. Chemoreceptors – membrane proteins that sense attractants and repellents; sense the concentration of particular chemicals and transduce this information to flagella, causing them to alter their rotation © 2021 Pearson Education, Ltd.  2.11 Chemotaxis Chemotaxis in Polarly Flagellated Bacteria polarly flagellated bacteria rely on Brownian motion (i.e., random movement) when stopped to reorient the cell © 2021 Pearson Education, Ltd.  2.11 Chemotaxis Measuring Chemotaxis Chemotaxis assay – a small glass capillary tube is immersed into a suspension of motile bacteria; chemical gradient extends from the tip of the capillary into the surrounding medium chemotactic bacteria will swim into the capillary even if it does not contain an attractant It is possible to quantify chemotactic behavior using a video camera that captures the positions of bacterial cells © 2021 Pearson Education, Ltd. with time and records the motility tracks of each cell  2.12 Other Forms of Taxis Osmotaxis – movement with respect to a gradient of ionic strength Hydrotaxis – movement with respect to a gradient of available water Aerotaxis – movement with respect to gradients of O2 Phototaxis – movement with respect to a gradient in light intensity © 2021 Pearson Education, Ltd.  2.12 Other Forms of Taxis Phototaxis Phototrophic purple bacteria placed on a microscope slide illuminated with a spectrum of light move preferentially toward certain wavelengths Scotophobotaxis – swim into darkness outside the illuminated field of view of the microscope; response only to the absence of light Photoreceptor - senses a gradient of light that interacts with the same cytoplasmic proteins that control flagellar rotation in chemotaxis © 2021 Pearson Education, Ltd.  2.12 Other Forms of Taxis Aerotaxis and Magnetotaxis Aerobic organisms require O2 and may exhibit a positive aerotactic response, swimming toward increasing concentrations of O 2. Microaerophiles often use aerotaxis to position themselves at an optimum concentration of O 2 (usually between 1% and 5% O2). Magnetosomes are found in specialized microaerophiles, referred to as magnetotactic bacteria. Magnetosomes allow magnetotactic bacteria to align themselves with these magnetic field lines. © 2021 Pearson Education, Ltd. ------ End of Presentation ------