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 growingE 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 2 n (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)

Temperature: Three groups Psychrophiles (cold loving): 5-20 degrees C –Psychrotrophs: degrees C Contribute to food spoilage in refrigerator Mesophiles (mod.- temp): degrees C –Most common –Often in animals Thermophiles (hot): 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 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 O 2 –Heated to drive off O 2

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 O 2 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: