Microbes Shape Our History Chapter 1 Notes

Microbes Shape our history Chapter 1 Chapter Objectives What is a Microbe? Microbes have shaped our: - Atmosphere - Geology - Energy Cycles Contribute to air we breathe Fix nitrogen into useable forms by plants Make essential vitamins - B12 Primary producers in food webs What is...

Microbes Shape our history Chapter 1 Chapter Objectives What is a Microbe? Microbes have shaped our: - Atmosphere - Geology - Energy Cycles Contribute to air we breathe Fix nitrogen into useable forms by plants Make essential vitamins - B12 Primary producers in food webs What is a Microbe? Humans have many partnerships with microbes - As many microbial cells as human - Food production and preservation - Mining for precious minerals - Biotechnology tools Small portion act as **pathogens** - Microbial allies outweigh our "enemies" What is a Microbe? Living organism that requires a microscope to be seen - Microbial cells range from mm to 0.2 µm (viruses much smaller) - Creates some contradictions - Some microbes can be seen without a microscope - Amoebas -- can span many millimeters Others form complex multicellular assemblages - Mycelia, biofilms Some multicellular organisms require microscopes to be seen -- not microbes - Mites What is a Microbe? Classified as members of a **species** - Shared genes and traits - Scientific names consist of **genus** and **species** - Genus capitalized while species lowercase, both italicized - *Staphylococcus epidermidis*, *Escherichia coli* - Classified according to genetic relatedness - Why does relatedness matter? - Relatedness is calculated by comparing DNA sequence in the **genome** What is a Microbe? Major trait used to distinguish microbes is presence or absence of a membrane enclosed nucleus **Prokaryotes** - Lack a nuclear membrane - Bacteria and archaea **Eukaryotes** - Possess a nuclear membrane - Fungi, protozoa, and algae What is a Microbe? **Prokaryotic** Bacteria - 0.2--20 µm - may grow as single cells, filaments, communities - ubiquitous - Archaea - genetically distinct from bacteria - "**extremophiles**" (methanogens) - nonpathogenic **Eukaryotic** Protozoa - motile, single-celled organisms - heterotrophs - may be free-living (ameba) or parasitic - Algae - contain **chloroplasts** and conduct **photosynthesis** - base of the food web - algal blooms What is a Microbe? **Eukaryotic** Fungi - nonmotile - **absorb** nutrients from surroundings - grow as single cells or as filaments - can cause disease, particularly in immunocompromised **Other** Viruses - **noncellular** - genetic material (DNA or RNA) - takes over the metabolism of a cell to generate more viruses - can cause disease - also used as biotechnology tools Microbes Shape Human History Have microbes affected human history? - Of course!! - Microbes have played an important role in human life - Microbes are responsible for killing more soldiers than war - Diseases have devastated human populations and changed cultural practices: - Tuberculosis - Leprosy - Smallpox - **Bubonic plague →** Renaissance - HIV - Catherine of Siena Viewing the Microbial World **Microscopes** revealed the microbial world [Robert Hooke] built first compound microscope - Only obtained 30x magnification [Antoine van Leeuwenhoek] was the first to observe single celled microbes - Cloth draper turned amateur microscopist - Spontaneous Generation **Spontaneous generation** -- theory that living microbes can arise spontaneously, without parental organisms [Lazzaro Spallanzani]: sealed flask experiment - Sealed flask of boiled meat broth grew no microbes - Cell fission [Louis Pasteur]: swan neck flask experiment - Began work as a chemist assisting with fermentation of alcohol - Swan neck flask permits air but no microbes to enter sterile medium - Even after Pasteur's experiment, debate remained - How might some organisms have been able to grow in a swan neck flask? - Medical Microbiology and Immunology By 18^th^ century the **germ theory of disease** developed - Specific diseases are caused by specific kinds of microbes [Florence Nightingale] noted connection between overcrowding and warfare with disease Used statistics to quantify role of disease in population mortality - Encouraged British government to improve hygiene Example of **epidemiology** in action - Public health Growth of Microbes in Pure Culture [Robert Koch] recognized the need for scientific method for identifying microbial cause of infectious disease - Anthrax, then tuberculosis - Pure cultures Growth of microbes in a **pure culture** is important for identification and patient diagnosis - Colonies - Petri dish - Agar - Demonstrated important principle of epidemiology -- **chain of infection** Developed first scientific method for establishing the microbial cause of a disease Koch's Postulates Problems: - Not all patients will experience symptoms for every disease - Some diseases are caused by exclusively human pathogens - Any others? - Immunization Prevents Disease - Identifying the cause of disease is only the first step - Lady Mary Montagu brought idea of **vaccination** from Turkey- introduced it to other parts of Europe - Still dangerous as some inoculated contracted serious disease - [Edward Jenner] used matter from cowpox lesions from milkmaids - Immunization - [Louis Pasteur] recognized that pathogens could be **attenuated** - He found attenuated microbes could not cause disease, but could provide **immunity** - Stimulating the immune system - **Immunization** -- stimulation of the immune response by intentional inoculation with a pathogen - Antiseptics and Antibiotics - Prior to work by Koch and Pasteur many patients died from infections transmitted by doctors - [Ignaz Semmelweis] promoted handwashing with **chlorine (an antiseptic)** prior to assisting with childbirth - Mortality rate of women during childbirth fell, still not widely accepted practice - [Joseph Lister] began sterilizing surgical instruments and wounds to create an **aseptic** environment for surgery - Received recognition with support from Koch and Pasteur - Fully developed aseptic environments for surgery by 20^th^ century - Antiseptics and Antibiotics - Antiseptics can't be taken internally - Researchers searched for a "magic bullet" - **Antibiotic** that will kill microbes but not harm the human host - Major advancement: realization that microbes produce antibiotic compounds - [Alexander Fleming] accidentally discovered penicillin as a contaminant on a plated culture of *Staphylococcus* - Noticed no growth around a mold contaminant on plate - Antiseptics and Antibiotics - In 1941 [Howard Florey] and [Ernst Chain] purified penicillin - Saved many Allied troop lives during World War II - First world war where antibiotics were available - Second half of 20^th^ century -- many power antibiotics discovered - Widespread and indiscriminate use of antibiotics has selected for **antibiotic resistant** pathogens - Multi-drug resistant strains of *M. tuberculosis* - Biotechnology is our tool in the "molecular arms race" - The Discovery of Viruses - Researchers were puzzled by the existence of disease causing microbes that could pass through filter pores that blocked larger microbial cells - Martinus Beijerinck studied tobacco mosaic disease - concluded it was caused by something small enough to pass through a filter - Wendell Stanley identified the filterable agent by crystallizing the infective particle from 4,000 kg of infected tobacco leaves - Tobacco mosaic virus - Microbes in Our Environment - Only about **0.1%** of microbial species can be cultured in the lab - Early microbiologist used nutrients that humans consume - Maybe some microbes require different nutrients? - Sergei Winogradsky -- studied microbes in wetlands - Found microbes that feed only on inorganic minerals (**lithotrophs**) - *Beggiatoa* fixes carbon into biomass without consuming an organic food - Developed **enrichment media** - Microbial ecologists demonstrated the role microbes play in **geochemical cycling** - Nitrogen fixation - Microbes in Our Environment Animals and Plants Evolved through Endosymbiosis - Microbial endosymbiosis is widespread in ecosystems - **Endosymbionts** -- organisms living symbiotically inside a larger organism - Lynn Margulis proposed that eukaryotic cells merged with bacteria to form composite cells - Respiring bacteria were engulfed by pre-eukaryotic cells and became mitochondria - Phototroph related to cyanobacteria were engulfed by eukaryotic cells and became chloroplasts - DNA sequence analysis showed that both of these organelles have circular DNA similar to modern bacteria - New Microbes Continue to Emerge - Microbe continued to be discovered even in habitats once thought uninhabitable - Hot springs of Yellowstone National Park - Bacterial DNA polymerase from this location is used in PCR technology - Carl Woese discovered that some organisms in Yellowstone have very different genomes than others - New prokaryotes were seen as distinct from of life -- the **archaea** - The DNA Revolution - Structure of DNA was determined using X-ray crystallography - Dorothy Hodgkin and [Rosalind Franklin] were pioneers - **Franklin** credited for discovering that DNA forms a double helix - She produced exceptional quality X-ray micrographs - Franklin's data was shared with **James Watson** - Along with **Francis Crick** they determined DNA bases pair in the interior of the DNA double helix - They published these findings without acknowledging Franklin