October 2 Flashcards
How do organisms deal with low aw?
In low water activity, an organism must obtain water from its environment by increasing its internal solute concentration and drawing water in by osmosis.
Internal solute concentration can be raised by pumping solutes into the cell or by synthesizing a solute.
In hypertonic solutions cells lose H2O
Compatible solutes counteract low aw in environment
Oxygen Classes of Microorganisms
Aerobes
Anaerobes
Facultative aerobes
aerotolerant aerobes
Microaerophiles
Aerobes
Require oxygen
Anaerobes
Do not require oxygen, some are killed by oxygen
Facultive aerobes
Can live with or without O2, can metabolize using aerobic or anaerobic methods
Aerotolerant Anaerobes
Can live in O2, but can’t use it
Microaerophiles
Use O2 in low amounts
How to test for Oxygen Requirements
Thioglycolate broth
Complex media with a small amount of agar making it viscous but still fluid
Thioglycolate reacts with O2 throughout the tube, O2 can penetrate only near the top of the tube
Catalase
Enzyme used to detoxify toxic forms of oxygen
Compare and Contrast Respiration and Fermentation
Fermentation: anaerobic, less ATP per molecule of glucose, e- acceptor/donor usually the same compounds
Respiration: aerobic or anaerobic, more ATP, glycolysis, e- acceptors different from e- donor, uses ETC
Fermentation
Lactic acid and mixed acid
No ETC
ATP produced via substrate level phosphylation
Classified by subrate fermentated or their products
Many organic compounds can be fermented
Lactic Acid Fermentation
Produces lactic acid from 2 pyruvate
homofermentive: only produces lactic acid
heterofermentive: produces lactic acid, EtOH, and CO2
Homofermentive
Only produce lactic acid
Lactobacillus acidophilus
Lactobacillus acidophilus
Homofermentive
found in yogurt
ferment lactose
lactic acid fermentation —> accumulation
Low pH inhibits growth of many microbes
Heterofermentive
Produces lactic acid, EtOH, and CO2
Leuconostoc mesenteroides
