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Microbial Growth What do they need to grow? • Physical needs – Temperature, proper pH, etc. • Chemical needs – Molecules for food, ATP production, coenzymes, etc. • Growth = increase in number, not size – Binary fission, some by budding – E coli growing • Generation time: doubling time – 1-2 hrs for most bacteria – E. coli can divide in 20 minutes in optimum conditions! What is the bacterial growth curve? • Graph shows a closed system • Lag phase – Cells acclimating – Preparing to divide • Log phase – Exponential growth – Generation time reaches constant minimum – Must susceptible to adverse conditions • Heat, radiation, drugs – Total growth • = # of cells X 2n • (n = number of generations) • Stationary phase – # dividing = # dying – Population stabilizes – Decrease in nutrients, increase in wastes • Death phase – # deaths > # new cells How can I measure bacterial growth directly? • Direct count – Plate counts – Serial dilutions • Then either pour plates or spread plates – Pro: only measures viable cells – Con: time consuming! Pro: only measures viable cells – Con: time consuming! How can I measure bacterial growth directly? • Direct microscopic count – Use gridded slide to count • Pro: no incubation time • Con: counts dead cells, too; hard to count moving bacteria – Take average and calculate back from dilution • Coulter counter How can I measure bacterial growth indirectly? • Turbidity – Cloudiness and more bacteria present – Use spectrophotometer • Percentage of transmission • Only works if you have at least a 1M cells per milliliter What are the physical requirements for growth? • Temperature – Each species has preferred temp range (over about 30 degrees C spread) – Dies quickly outside range • Minimum growth temp • Maximum growth temp • Optimum growth temp – Usually near top of range (close to max) What are the physical requirements for growth? • Temperature: Three groups • Psychrophiles (cold loving): 5-20 degrees C – Psychrotrophs: 20-30 degrees C • Contribute to food spoilage in refrigerator • Mesophiles (mod.temp): 25-40 degrees C – Most common – Often in animals • Thermophiles (hot): 4560 degrees C – Obligate thermophiles: only above 50 degrees C – Extreme thermophiles: above 80 degrees C • Archaea What are the physical requirements for growth? • pH – Most bacteria prefer 6.5-7.5 • When growing, pH changes • Additive to growth medium buffer pH – Phosphate salts, amino acids – Yeast, molds more tolerant of greater range • Optimum 5-6 • Acidophiles – Not many What are the physical requirements for growth? • Osmotic pressure – Bacteria are 80% to 90% water – Hypertonic solutions ________ water ____ cell • Results in plasmolysis – PM pulls away from cell wall – Retards bacterial growth – Why meat, butter, etc. salted – Extreme halophiles • Obligate halophiles – Bacteria in Dead Sea, 30% salt • Facultative halophiles – Can grow in up to 2% salt – Some in up to 15% – Salt not required for growth Anaerobic Culture Methods • Reducing media – Anaerobic jar – Contain chemicals (thioglycollate or oxyrase) that combine O2 – Heated to drive off O2 What are all the different “troph” types? Energy source: nonliving environment • Photoautotroph • Chemoautotroph Energy source: other organisms or sunlight • Photoheterotroph • Chemoheterotroph • Saprobe • Parasite What are the chemical requirements for growth? • Oxygen – Aerobe – Obligate aerobe – Anaerobe – Obligate anaerobe • Often harmed by oxygen • Clostriudium – Facultative anaerobe • Uses O2 when present • Can use anaerobic path or fermentation • E. coli – Aerotolerant anaerobes • Tolerate oxygen but don’t use it • Lactobacilli for cheese, pickles – Microaerophiles • Require oxygen at low concentration • Others include nitrogen, sulfur, phosphorus, etc. What are symbiotic relationships? • Mutualism – lichen • Commensalism – – – – Satellitism Microbial flora Lactobacillus E. coli • Parasitism What are non-symbiotic relationships? • Synergism – Roots & bacteria • Antagonism – Penicillium Photo from: http://scientificteaching.wisc.edu/products/PeanutFiles/imagesforsite/penicillium.jpg