An Overview of Microbiology

Transcription

1 An Overview of Microbiology Microbiology - The study of microscopic life - microorganisms Why study microorganisms? What are microorganisms? I. What is a cell? Cells are highly organized structures An organismʼs basic unit of structure and function. Cell provides for the following essential characteristics of life Order Reproduction Heredity Evolutionary adaptation Growth and development Metabolism Response to environment Homeostasis All cells are separated from the external environment by a plasma membrane All cells contain DNA at some stage in their lifetime. They are storehouses of information. Cells are also capable of interpreting this information Where did the first cells come from? All present day cells have apparently evolved from the same ancestor. 1

2 II. Cellular Organization Unicellular - single cell e.g., - bacterium Multicellular - cellular associations and differentiation but lack tissues (next level in the hierachy of biological organization) e.g., - filamentous blue green algae - mushrooms - fungal fruiting bodies i) Variation in cell size Smallest cell - mycoplasma (0.1 to 1.0 µm in diameter) Typical bacterial cells - 10 x larger (1 to 10 µm in diameter) Eukaryotic cells - 10 x larger than bacteria ( µm) Largest cell - Ostrich egg yolk - the size of a small orange (5-10 cm in diameter) Notable Exceptions Epulopiscium fishelsoni - Bacterial cell 60 X 800 µm Thiomargarita namibiensis - Bacterial cell up to 0.75 mm in diameter Nanochlorum eukaryotum - eukaryotic algae - cells 1 to 2 µm in diameter ii) Cell types Prokaryotic cell least complex no membrane bound nucleus no membrane bound organelles Domains: Bacteria and Archaea generally smaller Eukaryotic cell most complex membrane bound nucleus membrane bound organelles Domain Eukarya generally larger 2

3 iii) Viruses exception to the rule - acellular composed predominantly of protein and nucleic acid - lack cell or plasma membrane Not a dynamic open system like a cell They have no means of independent life support, rely on host's metabolic machinery if infect host they are capable of directing viral reproduction infect virtually all living cells Smallest virus is 10 nm in diameter; Largest viruses ~ 300 nm in diameter III Diversity of Life & Evolutionary Relationships > 1.8 million species have been identified. Taxonomy - The branch of biology concerned with the naming (nomenclature) and classification of organisms. Systematics - The study of biodiversity in an evolutionary context Taxonomic Hierarchies Organizational levels taxon (pl. - taxa) Ideally Represent a coherent degree of homology i.e., genetic and evolutionary similarity Members of each taxon should be monophyletic (i.e., same evolutionary history; members of a genus had a common ancestor) Taxa Domain Kingdom Phylum Class Order Family Genus Species Scientific Names 3

4 IV. Diversity of microorganisms Prokaryotes & Eukaryotes Metabolism Tolerance for extreme environments V. Ecology and Microorganisms An important consideration is that "populations of cells rarely live alone in nature" They usually live in association with other populations - microbial communities Population - an assemblage of a single type of cells (single species). May be clones of an original parental cell. Interactions occur within and between populations and also between the organisms and their physical and chemical environments (ecosystem) VI. Laboratory Culture We often grow microorganisms in the laboratory and in order to do this must provide the appropriate conditions for growth Culture medium (plural = media) - aqueous solution containing necessary nutrients Semisolid medium agar Pure culture - a culture containing a single cell type Sterilization Microbes are ubiquitous How can you produce a pure culture from a heterogeneous mixture? Aseptic technique - used to prevent contamination during manipulation of cultures and sterile media Sterilize all media and implements for handling materials of interest Clean working area Limit exposure to potential sources of contamination 4

5 Preparation of Pure Cultures Streak plate technique Dilution Deposition of individual cells or clumps of cells (known as colony forming units or CFU) on agar medium Cell growth multiplication resulting in the production of colonies (visible mass of cells) each isolated colony on the streak plate is assumed to have originated from a single CFU (It is unknown whether the cells in the colony came from a single cell or a clump of cells) VII History i) First observations of microorganisms Robert Hooke (1665) Anton van Leeuwenhoek Cell Theory Matthias Schleiden (botanist; 1838) & Theodor Schwann (zoologist; 1839) i) all living things consist of cells. ii) all cells come from preexisting cells. ii) Birth of Microbiology - Late 19 th century Ferdinand Cohn ( ) founder of bacteriology mid 1800s Discovered genus Bacillus and endospore formation Simple methods for preventing contamination of sterile culture media Louis Pasteur ( ) - father of microbiology mid to late 1800's Important discoveries Anaerobic life - life without oxygen Industrial Microbiology Ethanol fermentation Pasteurization Vaccines rabies, anthrax Disproved the theory of spontaneous generation 5

6 Robert Koch ( ) Germ theory of disease Koch's Postulates (Fig 14.3) used to prove that a specific type of organism is the cause (etiological agent) of a specific disease (i.e., Bacillis anthracis and anthrax) 1. The causative agent must be present in all "animals" with the disease and absent from healthy "animals". 2. The agent of disease can be isolated from the diseased "animal" and can be cultivated in pure culture in the laboratory 3. The disease can be reproduced by inoculating a portion of the laboratory culture into healthy "animals". 4. The agent of disease can be re-isolated from the infected "animal" and again cultivated in the laboratory. Pure culture technique iii) Vaccination Edward Jenner Used cowpox virus to vaccinate against smallpox virus Vaccines now produced against many infectious agents vaccines may be live attenuated or avirulent strains of microorganisms, killed microorganisms or specific components of the etiologic agents iv) Chemotherapeutic Agents Antimicrobial compounds may be synthetic or isolated from natural sources (antibiotics) Antibiotics - substances produced by microorganisms that kill (bacteriocidal) or prevent the growth (bacteriostatic) of other microorganisms. Alexander Fleming (Scottish bacteriologist) discovered antibiotics in 1928 with the discovery of penicillin produced by a fungus called Penicillium chrysogenum Selman Waksman - early 1940's discovered streptomycin - Streptomyces griseus 6

7 iv Microbial Ecology Early 1900's Martinus Beijerinck ( ) nitrogen fixation sulfur cycling enrichment technique - use of specific culture media and incubation conditions that favour growth of one type of microorganism while constraining the growth of others. Sergei Winogradsky ( ) nitrifying bacteria (NH 4 + NO 2 -) chemoautotrophs The role of microbes in biogeochemical processes v) Microbial Genetics and Molecular Biology One Gene - One Enzyme Hypothesis Beadle and Tatum (1941) Neurospora DNA - Hereditary Molecule Bacterial transformation Griffith (1928) Streptococcus pneumoniae - transforming principle Avery, McCarty, and MacLeod (1944) identified DNA as transforming principle Transduction Alfred Hershey and Martha Chase (1952) - Labelled T2 phage protein or DNA DNA Structure Watson and Crick (1953) Biotechnology & Recombinant DNA Technology Late 1970's until present 7

8 VII What is the impact of microorganisms on humans? 1) Environment A number of microorganisms are essential for the cycling of nutrients We use these microbial processes to treat sewage and remove toxic compounds from the environment (bioremediation) 2) Disease Agents Our bodies are colonized by many different microbial species - normal microbiota Diseases are caused by pathogens and diseases caused by microorganisms are called infectious diseases Emerging infectious diseases - 3) Agriculture Microorganisms affect agricultural productivity in a number of ways o cause diseases of crop plants and livestock o may also be beneficial to crop plants and animals o Biotechnological applications 4) Food Industry Microorganisms cause spoilage of food Microorganims are also used in the production of a number of food and beverages 5) Biotechnology "The industrial use of living organisms or their components to improve human health and food production" (Campbell et al., 1999) "Those processes in which living organisms are manipulated, particularly at the molecular genetic level, to form useful products" (Prescott et al., 1999) Biotechnology/Molecular genetics has been used to produce genetically modified organisms (GMO) for the following applications o Transgenic crop plants and livestock o Production of industrial chemicals and enzymes o Production of pharmaceutical compounds (i.e., insulin) o Medical treatments (gene therapy) 8