Prokaryotes: Bacteria and Archaea PDF

Topic 6 Prokaryotes: Bacteria and Archaea Learning objectives (LOBs) Describe the structure and morphology of prokaryotes Identify the role of pathogenic bacteria in human disease. Reading: Chapter 27 The Three Domains of Life Living organisms are classified into 3 domains: – Bacteria – Archaea – Eu...

Topic 6 Prokaryotes: Bacteria and Archaea Learning objectives (LOBs) Describe the structure and morphology of prokaryotes Identify the role of pathogenic bacteria in human disease. Reading: Chapter 27 The Three Domains of Life Living organisms are classified into 3 domains: – Bacteria – Archaea – Eukarya The Three Domains of Life Domain Bacteria and domain Archaea: – consist of unicellular prokaryotes Domain Eukarya: the eukaryotes, divided into 4 kingdoms – Protists – Fungi – Plants – Animals Life’s three domains 4 µm Bacteria are the most diverse and widespread prokaryotes and are now divided among multiple kingdoms. DOMAIN ARCHAEA Live in extreme environments, such 0.5 µm as salty lakes and boiling hot springs. Domain Archaea includes multiple kingdoms. The photo shows a colony composed of many cells. Protists are unicellular eukaryotes and some simple multicellular relatives. Scientists are currently debating how to split the protists into several kingdoms. Kindom Fungi is defined in part by the nutritional mode of its members, such as this mushroom, which absorb nutrients after decomposing organic material. Kingdom Plantae consists of multicellula eukaryotes that carry out photosynthesis, the conversion of light energy to food. Kindom Animalia consists of multicellular eukaryotes that ingest other organisms. Figure 1.15 Βasic categories of living organisms Prokaryotic Εukaryotic Μicroοrganisms Αrchaea Βacteria Protists Fungi Μacroοrganisms Do not exist Animals Plants Micro-organisms Μicro-organisms: Μicroscopic organisms consisting from either 1 cell (unicellular) or a group of cells (multicellular) Micro-organisms categories: - Βacteria: unicellular prokaryotic microorganisms - Αrchaea: unicellular prokaryotic microorganisms - Protists: eukaryotic microorganisms (e.g. protozoa, algae) - Fungi: eukaryotic microorganisms (e.g. yeasts, mushrooms) - Viruses: non-cellular pathogens Historical evidence for existence of micro-organisms Pathogenic micro-organisms cause infectious diseases Example: ¼ of the European population died of plague during Middle Ages Pasteur (1870): discovered the role of pathogenic bacteria in transmission of infectious diseases Koch (1892): discovered Vibrio cholerae as the pathogen that causes cholera Alexander Fleming (1929): discovered the antibiotic penicillin Infectious disease control due to discovery of antibiotics and vaccination History of pandemics viral bacterial 7 M (MAR 15, 2024, ONGOING) 0.06% 6.2M Yersinia pestis bacterium: caused plague (Black Death) World epidemics Disease Year Causative agent Deaths Antonine plague 165-180 Smallpox or measles 1 million Justinian plague 541-542 Yersinia pestis 30-50 million Japanese smallpox epidemic 735-737 smallpox 1 million Black Death 1347-1351 Yersinia pestis 200 million Smallpox 1520-1980 Variola major virus 56 million Italian plague 1629-1632 Yersinia pestis 1 million London plague 1655 Yersinia pestis 100 000 Cholera epidemics 1817-1923 Vibrio cholerae >1 million Third plague (China/India) 1885 Yersinia pestis 12 million Yellow fever (USA) End of 19th century Yellow fever virus 150 000 World epidemics Disease Year Causative agent Deaths Russian flu 1889-1890 H2N2 1 million Spanish flu 1918-1920 H1N1 40-50 million Asian flu 1957-1958 H2N2 1.1 million Hong Kong flu 1968-1970 H3N2 1 million AIDS 1981-present HIV 40 millions SARS 2002-2003 Coronavirus 770 Swine flu 2009-2010 H1N1 200 000 Ebola 2014-2016 Ebolavirus 11 000 MERS 2012- present Coronavirus 850 COVID-19 2019- present Coronavirus >7 millions (ongoing) Quarantine Historical facts: The word originates from the phrase quarantina giorni meaning 40 days Refers to the 40 day duration that Venetian ships coming from countries with active plague epidemics remained under quarantine in the sea before they approached Venice port Prokaryotes Unicellular micro-organisms Consist of 1 prokaryotic cell Replicate much faster than eukaryotes Smaller in size than eukaryotic cells Divided into 2 domains: - Βacteria - Αrchaea Can thrive almost everywhere, even under extreme conditions (too acidic, salty, cold, dry or hot for most other organisms) Domain Bacteria 2 major categories: - Εubacteria: includes pathogenic bacteria => cause diseases - Cyanobacteria: - non-pathogenic -have chlorophyll and perform photosynthesis => produce oxygen -live in lakes, oceans, etc -role in nitrogen fixation (conversion of nitrogen into ammonia => used by the plants) Domain Archaea Αrchaea (Archaebacteria): live in extreme conditions - Halophiles: - in salty lakes - Methanogens: - in the digestive track - anaerobes - produce methane - Thermoacidophiles: - in acidous, sulphur-rich hot springs - optimum temperatures of 70 - 80 ° C and pH 2-3 Archaea initially named Archaebacteria due to their morphological similarities with Bacteria However, phylogenetic analysis later on revealed a lot of molecular similarities with eukaryotes Prokaryotes: Bacteria and Archaea Εubacteria Cyanobacteria Αrchaea Βacteria Archaea Sulphur-rich hot springs Taxonomy: classification of living organisms Species Genus Ursus americanus (American black bear) Ursus Family Order Class Phylum Ursidae Carnivora Mammalia Chordata Animalia Figure 1.14 Eukarya Kingdom Domain Τaxonomy of living organisms Phylum Class Order Family Genus Species Sub-species Variety Strain (in Bacteria) Nomenclature of micro-organisms Same principles as the rest of the living organisms Binomial nomenclature: modern system of naming living organisms invented by Carolus Linnaeus (1707–1778) Species name = Genus + characteristic property Example: Staphylococcus aureus Staphylococcus=genus aureus= property Structural and functional properties of prokaryotes Earth’s first organisms were prokaryotes Prokaryotes are unicellular, but some species form multicellular colonies Prokaryotic cell size: 1–10 µm (smaller than eukaryotic cells: 10–100 µm) Variable morphology: a variety of shapes Morphology of Prokaryotes Spherical shape (cocci): -e.g. Staphylococci, Streptococci Rod-shaped (rods): e.g. bacilli (e.g. E.coli) Spiral shape: - e.g. Vibrio cholerae: shape C or S - e.g. Spirilla and Spirochetes 1 m 1 m 3 m Figure 27.2 (a) Spherical (b) Rod-shaped (c) Spiral Morphology of prokaryotes Differences between prokaryotic and eukaryotic cells Prokaryotic cell characteristics: Smaller in size Absence of nuclear membrane Absence of membrane-bound organelles (e.g. mitochondria or chloroplasts) No organised replicative cell cycle (mitosis)-replicate by binary fission instead Their cell wall has different composition from eukaryotic cell walls Prokaryotic-Eukaryotic cell morphology Prokaryotic cell Eukaryotic cell Lysosome Εndoplasmic reticulum Figure 27.UN03 Prokaryotic cell structure Fimbriae Cell wall Plasma membrane Nucleoid (region with circular chromosome) Capsule Sex pilus Cytoplasm Flagella Prokaryotic cell structure Cell-Surface Structures: Prokaryotic cell wall - Cell wall function: maintains cell shape protects the cell prevents cell from bursting in a hypotonic environment (osmotic pressure) - role in cell division Prokaryotic cell wall Eukaryotic cell walls: made of cellulose (plant cells) or chitin (fungi) Bacterial cell walls: contain peptidoglycan - Peptidoglycan: a network of polysaccharides and polypeptides Archaea cell wall: contain polysaccharides and proteins but lack peptidoglycan Peptidoglycan structure N-acetyl-glucosamine (NAG) N-acetyl-muramic acid (NAM) Oligopeptide chain Glycine residues (bridge) Gram staining: Gram (+) and Gram (-) bacteria Gram staining: staining technique used to classify bacteria in 2 major categories based on cell wall composition - the crystal violet dye used for staining (violet colour) 1. Gram-positive bacteria: - their cell walls mainly consist of peptidoglycan - they absorb crystal violet => purple (violet) colour 2. Gram-negative bacteria: - their cell walls consist of a small amount of peptidoglycan and large amount of lipopolysaccharides (LPS) - do not absorb crystal violet => pink colour Gram-positive and Gram-negative bacteria cell walls Plasma membrane Plasma membrane Figure 27.3 Gram - staining (a) Gram-positive bacteria: peptidoglycan traps crystal violet Gram-positive bacteria (b) Gram-negative bacteria: crystal violet is easily rinsed away => pink-red colour Gram-negative bacteria Carbohydrate portion of lipopolysaccharide Cell wall Peptidoglycan layer Cell wall Plasma membrane 10 m Gram (+) bacteria: purple (violet) Outer membrane Peptidoglycan layer Plasma membrane Gram (-) bacteria: pink Gram staining Gram (+) bacteria Gram (-) bacteria Gram (+) bacteria: cell wall structure Composition:peptidoglycan Examples of Gram (+) bacteria: - Staphylococci - Streptococci - Micrococci Gram (+) bacteria: Cell wall structure peptidoglycan Gram (-) bacteria: cell wall structure Composition: peptidoglycan + outer lipopolysaccharide (LPS) membrane Periplasm = Peptidoglycan + lipoproteins - space between inner and outer membrane Composition of outer LPS membrane: - phospholipids (PE, PG, DPG) - proteins: glycoproteins, lipoproteins - lipopolysaccharides (LPS) = lipids + sugars Examples of Gram (-) bacteria: Escherichia coli, Shigella, Salmonella Gram (-) bacteria cell wall structure Functional differences between Gram (+) and Gram (-) bacteria Gram (+) bacteria: peptidoglycan cell wall - Resistant to physical stress - Sensitive to lysozyme and penicillin Gram (-) bacteria: outer lipopolysaccharide layer - Resistant to lysozyme and penicillin Many antibiotics (e.g. penicillin) target the peptidoglycan and damage bacterial cell walls => Gram-negative bacteria are more likely to be antibiotic resistant Capsule Capsule: a polysaccharide or protein layer that covers some prokaryotes On the external side of the cell wall Only present in some prokaryotes Associated with the increased virulence of pathogenic bacteria Virulence: the ability of an infectious agent to produce disease => a measure of the severity of the disease it causes Capsule function Protects bacteria from phagocytosis by leukocytes Protects bacteria from digestion upon phagocytosis Protects them from infection by phages and drying Capsule Figure 27.4 Capsule Bacterial cell wall Bacterial capsule Tonsil cell 200 nm Fimbriae (pili) Some prokaryotes have fimbriae Number: 1-400 per bacterium Fimbriae function: - attachment of bacteria to each other or to other cells that they infect - Sex pili: special type of fimbriae (longer than regular fimbriae) that allow prokaryotes to exchange DNA Fimbriae Figure 27.5 Fimbriae Fimbriae 1 m Conjugation: DNA transfer between bacteria Conjugation: transfer of genetic material between prokaryotic cells through the sex pili Unidirectional process: one cell gives the DNA and the other cell receives Used for plasmid transfer from one bacterium to the other Plasmids: small circular extrachromosomal DNA molecules, some carry genes responsible for antibiotic resistance (R plasmids) The donor cell attaches to a recipient by a pilus, pulls it closer, and transfers DNA F plasmid: a plasmid required for the production of pili => the bacteria that have it act as DNA donors Figure 27.12 Conjugation Sex pilus 1 m Figure 27.13a-3 Conjugation: plasmid transfer between bacteria F plasmid Bacterial chromosome F+ cell F+ cell (donor) Mating bridge F− cell (recipient) Bacterial chromosome F+ cell Conjugation and transfer of an F plasmid Bacteria containing the F plasmid function as DNA donors during conjugation R Plasmids: Antibiotic Resistance R plasmids: carry genes for antibiotic resistance Antibiotics: drugs used to kill microorganisms (including bacteria) - However they cannot kill non-cellular pathogens such as viruses Bacteria with specific R plasmids are resistant to certain antibiotics R Plasmids: Antibiotic Resistance Natural selection favors the bacteria carrying genes for resistance in a population exposed to antibiotics  Antibiotic-resistant strains of bacteria are becoming more common (e.g. MRSA= methicillin resistant staphylococcus aureus)  Treatment of bacterial infections becomes harder  Antibiotics should only be used when truly necessary Antibiotics do NOT treat viral infections such as common cold and flu Frequent use of antibiotics leads to the development of resistance by the microorganisms => they are inactive when we need them Antibiotics: Do not over-use them! Motility of prokaryotes Taxis: the ability of bacteria to move toward or away from a stimulus Chemotaxis: the movement toward or away from a chemical stimulus Prokaryotic motility structures: - Flagella (most bacteria) - Αxial filaments (in Spirochetes) - Polysaccharide fibers (in Flexibacter polymorphus) Flagella Most motile bacteria propel themselves by flagella Flagella may be scattered about the surface or concentrated at one or both ends Flagella of Bacteria, Archaea, and Εukaryotes are composed of different proteins Type of movement: rotation (CW or CCW) Flagella Helical protein filaments Size: 3-12 μm long, diameter 0.02 μm 1-100 flagella per bacterium Categories of bacteria depending on location of flagella: - Monotrichous: 1 flagellum (e.g. Vibria) - Lophotrichous: multible flagella located at one end (e.g. Spirilla) - Amphitrichous: a single flagellum on each of two opposite ends - Peritrichous: have multiple flagella projecting in all directions (e.g. E.coli, Clostridium Parabotulinum) Flagella flagellum Types of bacteria depending on flagella location Μonotrichous Peritrichous Lophotrichous Types of bacteria depending on flagella location A= monotrichous B= lophotrichous C= amphitrichous D= peritrichous Prokaryotic flagellum structure Motor: responsible for rotation of flagellum - located within cell wall and plasma membrane - Energy for rotation comes from proton motive force (H+ pump) Hook: located just outside of cell wall Filament: - made by subunits of the protein flagellin - clockwise (CW) or counter-clockwise manner (CCW) rotation Figure 27.6 Prokaryotic flagellum structure Flagellum Filament Hook Motor Cell wall Plasma membrane Rod Peptidoglycan layer 20 nm Axial filaments In Spirochetes Located lengthwise between the bacterial plasma membrane and outer membrane (in the periplasmic space) Movement type: twisting motion (snake-like motion) Axial filaments Polysaccharide fibers Some bacteria move by crawling or sliding (e.g. Flexibacter polymorphus) using polysaccharide fibers instead of flagella Cytoplasmic membrane (plasma membrane) Composition:phospholipids and proteins Phospholipids in prokaryotic plasma membrane: - Phosphatidyl-glycerol (PG) - Phosphatidyl-ethanolamine (PE) - Phosphatidic acid (PA) - Diphosphatidyl-glycerol (DPG) Selectively permeable (semi-permeable) Membrane lipids Lipid composition (%) of different membranes Lipids Plasma membrane Hepatocytes Erythrocytes Myelin Mitochondria Bacteria Cholesterol Phosphatidyl-ethanolamine Phosphatidyl-serine Phosphatidyl-choline Phosphatidy-inositol Phosphatidyl-glycerol Sphingomyelin Cerebrosides Various lipids Adapted from: Margaritis et al, Biology of the Cell. Plasma membrane Proteins Phospholipids Internal Organization and DNA Prokaryotic cells lack complex compartmentalization They do not have a membrane-bound nucleus and membrane-bound organelles Mesosomes: - infoldings of the plasma membrane - specialized membranes that perform metabolic functions in some prokaryotes - Function: - cellular respiration (in aerobic prokaryotes) or photosynthesis (e.g. in cyanobacteria) - Formation of diaphragm during cytokinesis Figure 27.7 Mesosomes 1 m 0.2 m Respiratory membrane Thylakoid membranes (a) Aerobic prokaryote (b) Photosynthetic prokaryote Prokaryotic ribosomes Ribosomes= RNA + proteins Function: protein synthesis Polysomes = ribosomes + mRNA Prokaryotic ribosomes consist of different subunits than eukaryotes - 30S (small subunit) and 50S (large) subunits => Some antibiotics (e.g. tetracycline) inhibit bacterial ribosomes without inhibiting human (eukaryotic) ribosomes Nucleoid Nucleoid: the region that contains the prokaryotic chromosome, not surrounded by a nuclear membrane Prokaryotic chromosome = double-stranded circular DNA molecule - Smaller than eukaryotic genome - Αbsence of histones (only present in eukaryotic chromosomes) - Supercoiled to fit the nucleoid region Nucleoid Prokaryotes may contain extra-chromosomal elements: - Plasmids: small circular DNA molecules, some carry genes responsible for antibiotic resistance (R plasmids) - Βacteriophages (phages): viruses that infect bacteria (have DNA genome) Prokaryotic chromosome DNA strands Figure 27.8 Prokaryotic chromosome Chromosome Plasmids 1 m Plasmids: extra-chromosomal elements Endospores Some prokaryotes are sporogenic => they have the ability to form endospores (spores) Endospores are formed under harsh conditions (e.g. very high or very low temperature, dry environment) Εndospores: - metabolically inactive - remain viable in harsh conditions for years - resistant to temperature, dryness, UV light, enzymes, chemicals and drugs The endospores can grow back to the prokaryotic (vegetative) cell once in optimal conditions Examples of sporogenic bacteria: Bacilli, Clostridia Endospore structure Cytoplasmic membrane Cortex: resistance to high temperature Coat Εxospore Figure 27.9 Endospore Endospore Coat 0.3 m Bacillus anthracis: causes anthrax Reproduction and adaptation Key features of prokaryotic reproduction: – They reproduce quickly by binary fission – They have short generation times (can divide every 1–3 hours) Their short generation time allows rapid evolution of prokaryotes => adaptive evolution of bacteria (adaptation) – Example of adaptive evolution of bacteria: development of antibiotic resistance Prokaryotes are not “primitive” but are highly evolved Binary Fission Origin of replication 1 Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. 2 Replication continues. One copy of the origin is now at each end of the cell. 3 Replication finishes. The plasma membrane grows inward (mesosomes), and new cell wall is deposited (cell plate formation). Figure 12.11 4 Two daughter cells result. Cell wall E. coli cell Two copies of origin Origin Plasma Membrane Bacterial Chromosome Origin Genetic diversity in prokaryotes Prokaryotes have considerable genetic variation Three factors contribute to this genetic diversity: – Rapid reproduction – Mutation – Genetic recombination Rapid reproduction accumulation of mutations in a prokaryotic population high genetic diversity rapid evolution Genetic Recombination Genetic recombination: combination of DNA from two sources => contributes to genetic diversity Horizontal gene transfer: movement of genes among individuals from different species => Prokaryotic DNA from different individuals can be brought together by: - Transformation: uptake and incorporation of foreign DNA by prokaryotic cells from their surroundings - Transduction: the exchange of DNA between bacteria mediated by bacteriophages (viruses that infect bacteria) - Conjugation: transfer of genetic material between prokaryotic cells in direct contact (through sex pili) Figure 27.11-4 Phage Transduction A+ B+ Donor cell A+ B+ A+ Recombination A+ A− B− A+ B− Recipient cell Recombinant cell Nutritional and metabolic adaptations in prokaryotes Prokaryotes are categorized in 4 groups based on their energy and carbon source: – Phototrophs: obtain energy from light – Chemotrophs: obtain energy from chemicals – Autotrophs: require CO2 as a carbon source – Heterotrophs: require an organic nutrient as a carbon source Nutritional and metabolic adaptations in prokaryotes Four major categories based on mode of nutrition: – – – – Photoautotrophs Chemoautotrophs Photoheterotrophs Chemoheterotrophs Table 27.1 (e.g. purple-sulphur bacteria) (e.g. purple and green nonsulphur bacteria) Oxygen Metabolism Prokaryotes are categorized based on their ability to metabolize oxygen: – Obligate aerobes: require oxygen for cellular respiration – Obligate anaerobes: poisoned by oxygen and use fermentation or anaerobic respiration – Facultative anaerobes: can survive with or without oxygen Nitrogen Metabolism Nitrogen is essential for the production of amino acids and nucleic acids Prokaryotes can metabolize nitrogen in a variety of ways Nitrogen fixation: conversion of atmospheric nitrogen (N2) to ammonia (NH3) by some prokaryotes Prokaryotic phylogenic taxonomy using molecular systematics Until 20th century, prokaryotic taxonomy based on phenotypic criteria (morphology) Phylogenic taxonomy: the study of evolutionary relationships among groups of organisms using molecular sequencing data and morphological data Molecular systematics: molecular sequencing data Molecular systematics application to prokaryotic phylogeny investigation => splitting of prokaryotes into Bacteria and Archaea Molecular systematics: continues work on the phylogeny of prokaryotes Polymerase chain reaction (PCR): rapid sequencing of prokaryotic genomes Many new groups of Archaea revealed Figure 27.15 Eukaryotes Euryarchaeotes Crenarchaeotes UNIVERSAL ANCESTOR Nanoarchaeotes Domain Archaea Korarchaeotes Domain Eukarya Phylogenic taxonomy of Prokaryotes Proteobacteria Spirochetes Cyanobacteria Gram-positive bacteria Domain Bacteria Chlamydias Figure 27.UN01 Eukarya Archaea Bacteria Archaea Archaea morphologically resemble Bacteria However, they share certain traits with Bacteria and other traits with Eukaryotes Most archaea live in extreme environments (extremophiles) - Extreme halophiles: live in highly saline environments - Extreme thermophiles: thrive in very hot environments - Methanogens: - live in swamps, marshes and digestive track - produce methane as a waste product - obligate anaerobes (poisoned by oxygen) Table 27.2 Figure 27.16 Archaea: thermophiles Bacteria Bacteria include the vast majority of prokaryotes of which most people are aware Major groups (phyla) of bacteria: 1. Proteobacteria 2. Cyanobacteria 3. Chlamydia 4. Spirochetes 5. Gram-positive bacteria Figure 27.17a Proteobacteria These are Gram-negative bacteria Includes several pathogenic species Alpha Beta Gamma Delta Epsilon Proteobacteria Figure 27.17-a Proteobacteria subgroups Subgroup: Alpha Proteobacteria Subgroup: Beta Proteobacteria Alpha 2.5 m Gamma Proteobacteria Delta Epsilon Rhizobium (arrows) inside a root cell of a legume (TEM) Nitrosomonas (colorized TEM) Subgroup: Delta Proteobacteria Subgroup: Epsilon Proteobacteria Thiomargarita namibiensis containing sulfur wastes (LM) Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) 2 m 300 m 200 m Subgroup: Gamma Proteobacteria 1 m Beta Helicobacter pylori (colorizedTEM) Subgroup: Alpha Proteobacteria Many species of this subgroup are closely associated with eukaryotic hosts (symbiosis) Endosymbiotic theory: mitochondria have evolved from aerobic alpha-proteobacteria through endosymbiosis Examples: - Rhizobium: forms root nodules in legumes and fixes atmospheric N2 - Agrobacterium: produces tumours in plants and is used in genetic engineering Subgroup: Beta-Proteobacteria (pathogenic) Neisseriae: Bordetella pertussis: causes whooping cough (pertussis) Neisseriae morphology: Diplococci (EM) Meningococcal septicaemia Subgroup: Gamma Proteobacteria Examples: Pathogenic bacteria: e.g. Legionella, Salmonella, and Vibrio cholerae Opportunistic pathogens: - Escherichia coli: - resides in the intestines of many mammals and is not normally pathogenic but part of the normal flora - However, it can cause opportunistic infections in immunosuppressed patients (e.g. AIDS patients, patients receiving chemotherapy or immunosuppressive drugs) - Some strains can cause haemorrhagic diarrhoea Ε. coli Gram staining Salmonella enteritidis EM Vibrio cholerae Vibrio cholera: causes cholera - Symptoms: prolonged diarrhoea (5-15 days) -Transmission via contaminated, non-chlorinated water, in undeveloped countries -Toxin production (e.g. enterotoxin) => dehydration and death Morphology Dehydrated patient due to continuous diarrhoea Figure 27.17e Subgroup: Delta Proteobacteria No pathogenic species 300 m Subgroup: Delta Proteobacteria Fruiting bodies of Chondromyces crocatus, a myxobacterium (SEM) Example: slime-secreting myxobacteria (soil decomposers) Subgroup: Epsilon Proteobacteria Contains many pathogens: - Campylobacter: causes food poisoning (complications: blood poisoning) - Helicobacter pylori: causes stomach ulcers and gastric cancer Helicobacter pylori (colorized TEM) Ηelicobacter pylori Gastritis, ulcers, gastric cancer Ηelicobacter pylori Other Bacteria groups Spirochetes 5 m 2.5 m Chlamydias Leptospira, a spirochete (colorized TEM) Chlamydia (arrows) inside an animal cell (colorized TEM) Cyanobacteria 40 m 5 m Gram-Positive Bacteria Oscillatoria, a filamentous cyanobacterium Streptomyces, the source of many antibiotics (SEM) 2 m Figure 27.17-b Hundreds of mycoplasmas covering a human fibroblast cell (colorizedSEM) 2. Chlamydias Obligate parasites that live within animal cells Chlamydia trachomatis: causes non-gonococcal urethritis (sexually transmitted disease, STD) Chlamydia (arrows) inside an animal cell (colorized TEM) Scarring of fallopian tubes=> infertility 3. Spirochetes Spiral-shaped bacteria Some are parasites: - Treponema pallidum: causes syphilis (sexually transmitted disease) - Borrelia burgdorferi: causes Lyme disease (transmitted by ticks) "classic“ bull's-eye rash (erythema) Leptospirosis: symptoms Leptospira: a spirochete (colorized TEM) Jaundice (due to liver infection) Kidney infection Zoonosis= transmitted by animals(rodents) 4. Cyanobacteria Photoautotrophs => generate oxygen by photosynthesis Endosymbiotic theory: Chloroplasts likely evolved from cyanobacteria by endosymbiosis Oscillatoria, a filamentous cyanobacterium 5. Gram-Positive Bacteria Gram-positive bacteria include several pathogenic species: – Actinobacteria (Actinomycetes): soil decomposers, cause cutaneous infections – Bacillus anthracis: causes anthrax – Corynebacterium diphtheriae: causes diphtheria – Clostridium botulinum: causes botulism – Clostridium tetani: causes tetanus – Several Staphylococcus and Streptococcus species: e.g. Staphylococcus aureus, Streptococcus pneumoniae – Mycobacteria: Mycobacterium tuberculosis and Mycobacterium leprae – Mycoplasmas: the smallest known cells (no cell wall) Figure 27.17j 5 m Gram-Positive Bacteria: Actinomycetes Streptomyces: the source of many antibiotics (e.g streptomycin) Actinomycoses: infections caused by Actinomycetes Bacillus anthracis: causes athrax Gram staining (CSF) Clostridium botulinum Contaminates improperly canned food Produces the neurotoxin botulinum toxin (botox)=> causes botulism Causes paralysis by inhibiting the release of the neurotransmitter acetylcholine at the neuromuscular junction synaptic cleft Death due to respiratory muscle failure Clostridium tetani Causes tetanus (τέτανος = stretch). Symptoms: convulsive muscle spasms (convulsions of skeletal muscle) and paralysis Due to toxin production => can be fatal if untreated Transmission: bacteria enter through a break in the skin (cut/puncture wound) by a contaminated object Characteristic “arching” muscle spasms associated with tetanus Corynebacterium diptheriae Causes diphtheria (a serious upper respiratory tract infection) Characteristic symptoms: - Pseudomembrane formation in the pharynx, trachea, etc - Diphtheria toxin: inhibits protein synthesis (translation) => cell/tissue and organ damage Pseudomembranes (dead tissue) Gram-Positive Bacteria: Mycoplasmas 2 m Μycoplasma hominis and Ureaplasma urealyticum - Cause non-gonococcal urethritis Figure 27.17k Mycoplasmas covering a human fibroblast cell (colorized SEM) Mycobacteria and Mycoplasmas Both genera include species that are phylogenetically Gram+ but structurally neither Gram+ nor Gram– That’s because they do not absorb the crystal violet dye Εxplanation: Mycoplasmas: don’t have a cell wall => they cannot be classified as Gram+ or – according to the wall. Mycobacteria: have a unique lipid-rich (waxy) cell wall (do not have the LPS outer layer that Gram- bacteria have). Therefore, we use other types of dyes, such as methylene blue, to stain these types of bacteria. Mycobacteria are classified as acid-fast (resistant) Gram-positive bacteria due to their lack of an outer (LPS) layer. Prokaryotes roles in the biosphere Chemical recycling Ecological interactions Chemical Recycling Prokaryotes are involved in recycling of chemical elements between the living and non-living components of ecosystems Decomposers: chemoheterotrophic prokaryotes that break down dead organisms and waste products Prokaryotes can increase the availability of nitrogen, phosphorus, and potassium for plant growth => used in fertilizers e.g. bacteria in fertilizers Ecological Interactions Symbiosis: an ecological relationship in which two species live in close contact Host: the larger organism Symbiont: the smaller organism Prokaryotes often form symbiotic relationships with larger organisms Types of symbiotic relationships: -Mutualism: both symbiotic organisms benefit -Commensalism: one organism benefits while neither harming nor helping the other organism - Parasitism: an organism called a parasite harms but does not kill its host -Parasites that cause disease are called pathogens Prokaryotes have both beneficial and harmful impacts on humans Pathogenic prokaryotes Beneficial prokaryotes Beneficial prokaryotes: Mutualistic Bacteria Part of our normal flora About 500–1000 species of bacteria live in the human intestines Many of these break down food that is undigested by our intestines (cannot be digested by our own enzymes) Pathogenic Bacteria Pathogenic prokaryotes cause about 50% of all human diseases Pathogenic prokaryotes typically cause disease by releasing toxins Exotoxins: - Products of bacterial metabolism - cause disease even if the prokaryotes that produce them are not present - Mainly secreted by Gram (+) bacteria Endotoxins: - Lipopolysaccharides (LPS) part of the outer membrane of the Gram (-) bacteria cell wall - released when bacteria die (due to phagocytosis) and their cell walls break down Pathogenic bacteria cause infectious diseases Pathogenic Bacteria Horizontal gene transfer can spread genes associated with virulence (e.g. by conjugation) Horizontal gene transfer: movement of genes among individuals from different species Some pathogenic bacteria are potential weapons of bioterrorism (e.g. Bacillus anthracis) Common pathogenic bacteria species Staphylococcus aureus: causes toxic shock syndrome, food poisoning (gastroenteritis), pneumonia - MRSA= methicillin-resistant strain of St. aureus Streptococcus pneumoniae (pneumococcus): causes pneumococcal meningitis Bacillus cereus: causes food poisoning (gastroenteritis) Neisseria meningitidis (meningococcus): causes meningococcal meningitis Νeisseria gonorrhoeae (gonococcus): causes gonococcal urethritis (gonorrhea, STD) Escherichia coli (E.coli): opportunistic infections Mycobacterium tuberculosis: causes tuberculosis Mycobacterium leprae: causes leprosy Staphylococcus aureus Gram staining (LM) Colonies (EM) Staphylococcus aureus infections Streptococci Gram staining Colonies form chains (LM) Various Streptococcal infections Pneumococcal meningitis Meningitis due to pneumococcus (Streptococcus pneumoniae) Streptococcus pneumoniae in CSF (400x) of meningitis patient septicaemia Mycobacterium tuberculosis Tuberculosis: lung infection characterised by chronic cough with blood-containing sputum M. tuberculosis presence in patient sputum M. tuberculosis (EM) Mycobacterium leprae: causes leprosy Prokaryotes in Research and Technology Prokaryotes used in DNA technology (engineering): – E. coli is used in gene cloning – Agrobacterium tumefaciens: used to produce transgenic plants (GMOs) Bacteria can be genetically engineered to produce vitamins, antibiotics, and hormones (e.g. insulin production) Summary: human pathogenic Bacteria Species /Genus name Disease Bacterial group/subgroup Neisseria meningitidis (meningococcus) Νeisseria gonorrhoeae (gonococcus) Meningococcal meningitis Beta-proteobacteria Gonococcal urethritis (gonorrhoea; STD) Beta-proteobacteria Escherichia coli Opportunistic infections (e.g. gastroenteritis, haemorrhagic diarrhoea) Gastroenteritis (food poisoning) Gamma-proteobacteria Salmonella enteritidis Legionella Legionnaires' disease (legionellosis) Gamma-proteobacteria Gamma-proteobacteria Vibrio cholerae Cholera Gamma-proteobacteria Campylobacter Food poisoning, blood poisoining Epsilon-proteobacteria Helicobacter pylori Gastritis, stomach ulcers and gastric cancer Epsilon-proteobacteria Treponema pallidum Syphilis (STD) Spirochetes Borrelia burgdorferi Lyme disease Spirochetes Leptospira Leptospirosis Spirochetes Summary: human pathogenic Bacteria Species /Genus name Disease Bacillus cereus Food poisoning (gastroenteritis) Gram-positive bacteria Bacillus anthracis Anthrax Gram-positive bacteria Clostridium botulinum Botulism (paralysis) Gram-positive bacteria Clostridium tetani Tetanus Gram-positive bacteria Actinomycetes (Actinobacteria) Actinomycoses (skin infection) Gram-positive bacteria Staphylococcus aureus Toxic shock syndrome food poisoning (gastroenteritis), pneumonia Gram-positive bacteria Pneumococcal meningitis Gram-positive bacteria Tuberculosis Gram-positive bacteria Mycobacterium leprae Leprosy Gram-positive bacteria Mycoplasma hominis Ureaplasma urealyticum Chlamydia trachomatis Non-gonococcal urethritis (STD) Gram-positive bacteria Non-gonococcal urethritis (STD) Chlamydias Streptococcus pneumoniae (pneumococcus) Mycobacterium tuberculosis Bacterial group/ sub-group Summary: human pathogenic Bacteria Species /Genus name Disease Bacterial group/subgroup Corynebacterium diphtheriae Diphtheria Gram-positive bacteria Clostridium tetani Tetanus Gram-positive bacteria Bordetella pertussis Pertussis (whooping cough) Beta-proteobacteria DTP vaccine: anti-bacterial vaccine (Diphtheria-Tetanus-Pertussis) Prokaryotic cell structure Structure Function Cell wall Protects cell from mechanical damage/osmotic pressure Cell (plasma) membrane Semi-permeable=> controls what enters/exits the cell Capsule (only in some prokaryotes) Protects bacteria from phagocytosis/digestion/drying Fimbriae (only in some prokaryotes) Attachment of bacteria to each other or to other cells that they infect Sex pili (special type of fimbriae Allow prokaryotes to exchange DNA longer than regular fimbriae; in some prokaryotes) Flagella (only in some prokaryotes) Motility (movement) Nucleoid Region where bacterial chromosome is found SBA example 1 What disease does Neisseria meningitidis cause? A. B. C. D. E. Botulism Gastroenteritis Gonorrhea Meningitis Tetanus SBA example 2 What bacterial group does Leptospira belong to? A. B. C. D. E. Chlamydias Cyanobacteria Gram-positive bacteria Proteobacteria Spirochetes