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Midterm

MICR 2420 Post Midterm 1 Notes

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Department
Microbiology
Course
MICR 2420
Professor
Steven Seah
Semester
Winter

Description
MICR 2420 Post Midterm Microbial Growth & Nutrition Counting Bacteria and Bacteria Growth Cycle  Bacteria need to be in liquid in order to be counted  Solid samples must be suspended in liquid  Expressed in terms of: o #bacteria/mL of liquid o #bacter/g of solid Direct Microscopic Count  Microorganisms are counted directly by placing dilutions on a special slide called a Petroff- Hausser counting chamber  Slide has wells and an etched grid  Ex: -6 Within the large square, it can hold 8.0 x10 , there is 7 microbes. 7/8.0 x10-6 = 8.75x10 bacteria/mL Plate Count  Theory is that one bacteria can form a colony  One of the most commonly used  Important to dilute so you don’t have too many colonies form  Use between 30-300 colonies Fluorescent-activated Cell Sorter  Fluorescent tagged cells are passed through a small orifice and passed a laser  Detectors measure light scatter in the forward direction (measure of particle size) and to the side (particle shape or granularity)  Very expensive, and few labs have them Advantages Disadvantages Direct count Cheap Hard to count motile bacteria Hard to count when liquid is opaque Plate count Cheap Need right dilution for countable number of colonies No motility issues FACS Accurate Expensive Need fluorescent tag It dirty, it will count dirt particles as cells Microbial Growth & Cell Division  Bacteria divide by binary fission, where one cell makes two  Two daughter cells are identicle  Bacteria x 2^(number of divisions) = total bacteria Batch Culture 1. lag phase – bacteria are preparing their cell machinery for growth 2. log phase – growth approximates an exponential curve 3. stationary phase – cells stop growing and shit down growth machinery while turning on stress response to help retain viability 4. death phase – cells die with a ‘half-life’ similar to radioactive decay, a negative exponential curve Continuous Culture  an open system where fresh medium is continuously added and an equal amount of waste is removed  can maintain bacterial populations longer  human GI tract works this way Biofilms  many bacteria in nature form specialized, surface attached communities called biofilms  can be constructed by one or multiple species and can form on a range of organic or inorganic surfaces  held together by exopolysaccharides, a secreted polymer of sugar  more resistant to antibiotics, need a higher dose to kill them  when stuck, bacteria on the bottom/inside have less access to nutrients  they can cause diseases in o catheters o lungs – pneumonia o prosthetics o gums/teeth o stomach  in the environment o can colonize in pipes and block them o found in hot springs in Yellowstone o stromatolites are fossilized biofilms  biotechnological applications o waste water treatment  bacteria that clean the water form a biofilm  become denser than water  sink to the bottom and separate from clean water o microbial fuel cells A Microbe Diet: How to grow bacteria in the lab Organic Macroelements  Carbon, oxygen, hydrogen o Constituents of major biological molecules: carbs, proteins, lipids, nucleic acids  Nitrogen o Constituent of proteins, nucleic acids, amino acids  Phosphorus o Constituent of nucleic acids, phospholipids  Sulfer o In some amino acids and proteins Inorganic Macroelements  Metal ions: potassium, calcium, magnesium, sodium, iron o Required in some enzymes o Electron carriers o Membrane stability Trace Elements  Metal ions: iron, cobalt, manganese, molybdenum, zinc, copper, nickel, chromium, selenium, tungsten o Not all bacteria require these o Required for some enzymes Supplements: vitamins, amino acids, nucleotides etc. NASA & Alien Bacteria  Nasa though to have discovered bacteria that used arsenic in place of phosphorus  Had an arsenic DNA backbone  Not possible because arsenic ester bonds are weak compared to phosphorus and very unstable in water o They would fall apart in the cytoplasm Exxon Valdez Oil Spill  Bioremediation: use of living organisms to clean up waste  Crude oil = mixture of water souble hydrocarbons o There are bacteria that can degrade these hydrocarbons  Bioaugmentation: the introduction of a group of natural microbial strains or a genetically engineered variant to treat contaminated soil or water Bacteria Growth Media in the Lab Defined Media  The precise chemical composition of the media is known  Instead of using a carbon source like glucose, it can be
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