Microbial Metabolism and Growth

Microbial Growth

• Bacteria reproduce by Binary Fission

• cell division can occur rapidly depending in nutrient levels, etc.

• Ex: E. Coli can divide every 20 min at 37 degrees C

Two major factors

• Environmental factors: temp, pH, Osmotic conditions

• Chemical: proper concentrations of C, H, O, N, P, S, some trace elements, and some organic cofactors

Endospore

• dormant stage

• cells hang out till things get better

• don’t have a death phase

Direct cell count

• use stained slides that have a grid for counting

• tedious and time consuming

• difficult to know if it is living or is it dead

Indirect Cell Count

• serial dilution

• plates are inoculated

• incubated and colonies counted

• Number of colonies X dilution factor = # of bacteria

• can tell if dead or alive

Other ways of measuring

• Spectrometer

  • measure cloudiness in a test tube as the number of cells increase

• Coulter counter

  • electronically counts number of bacteria as bacteria passes through a tiny tube

Mesophiles

• grow best in moderate temp

• 25-40

• most of our lab microbs

Psychrophiles

• adapt and grow at cooler temp

• below 25

• Listeria

Thermophiles

• high temps

• Thermus aquaticus - survives at 60 degrees

Leprosy bacilli

• prefer 30 degrees

• most pathogens prefer 37 degrees

pH

• bacteria grow best at 6.5-7.5

• Fungi at slightly acidic 5-5.5

• Helicobacter pylori - survives stomach acid

Hydrostatic Pressure

• some bacteria grow well in ocean at pressures that can crush submarines like an egg

Osmotic pressure

Hypertonic → higher salt

• Halophiles, Vibrio bacteria, V. cholera

Nutrients

• Autotrophs: producers, make own food

• Heterotrophs: require preformed food, most microbes

• Chemoautotrophs: unique metabolism, use chemical energy from inorganic molecules

Oxygen

• Obligate aerobes: require molecular oxygen

• Obligate anaerobes: require no oxygen

  • organic molecule as final electron acceptor

  • Clostrida

• Facultative anaerobes - with or w/o Oxygen

• Microaerophile: grow best in lower oxygen and high CO2

Oxygen is toxic

• oxidizes and destroys vital cell chemicals

• SOD: superoxide dismutase

  • enzyme that makes toxic oxygen into less toxic hydrogen peroxide

• Catalase: converts hydrogen peroxide to oxygen and water

Fastidious

• hard to grow

• need enriched media (blood, egg)

• impossible parasitic-fastidious nature (syphilis, leprosy)

Catabolism

• makes ATP

Adenosine Triphosphate (ATP)

• ribonucleotide

• phosphate, adenine, ribose

• made, energy stores, broken down, release energy

Enzymes

• lower EA

• organic catalyst

• protein

Three stages

1. Glycolysis

   1. anaerobic

   2. cytoplasm

2. Krebs cycle

   1. mitochondria

   2. aerobic

3. Electron transport (with chemiosmosis)

   1. Aerobic

   2. mitochondria

Krebs cycle

• series of oxidation steps

fermentation

• many microbes ferment sugars and other substrates to make ATP without oxygen

• products: ethanol, CO2, lactic acid, acetic, acid

• microbes can use a different electron acceptor

Pentose Phosphate pathway

• ribose 5 phosphate metabolism protects E. coli from antibiotic lethality