Chapter 4 Flashcards
(44 cards)
Robert Koch
Studies disease causing bacteria
Developed methods to cultivate bacteria
1882 Fannie Hess suggested Agar
Generation time
Time it takes for bacteria population to double
Varies, environmental conditions
Microbial Growth formula
N_t= N_0 x 2^n
N_t is the # of cells in population at time t
N_0 is the initial number of cells
n is the number of generations at that point
Biofilm formation and structure
Free cells adhere to surfaces and multiply
Extra polymeric substances give slimy appearance
Cells communicate via chemical channels
Microorganisms friend or foe
Friend
Can foster growth of species otherwise an able to survive
Metabolic waste of one can serve as nutrient for other
Foe
Some synthesize toxic compounds to inhibit competitors
Gram negative bacteria use a needle like structure called type VI to inject toxic compounds into competing bacteria
Pure culture
Population of cells derived from a single cell; allows study of a single species
Only 1% of microorganisms can be cultured
Culture medium: What is used to grow cells, contains nutrients and it can be a liquid broth or solid gel
Stock culture
Maintained pure culture
Cells can be frozen at -70°C or freeze dried for long term storage
Glycerol to prevent ice
Closed system or batch culture
Culture in which nutrients are not added, nor are wastes removed
Agar plates, tubes, or flasks of broth
The growth curve
Lag phase
Exponential log phase
Stationary phase
Death phase
Phase of prolonged decline
Lag phase
No increase in cells
Cell synthesize growth enzymes
Delay depends of conditions
Exponential log phase
Cell divide constantly (generation time)
Most sensitive to antibiotics
Primary metabolites: are produced, such as amino acids
Secondary metabolites: such as antibiotics are produced as waste accumulate
Stationary phase
Nutrient levels too low to sustain growth
Some die, some grow
Secondary metabolites still produced
Death phase
Viable cells decrease
Cells die constantly
Phase of prolonged decline
Some fraction may survive
Those that adapted to conditions
Positions of colony
Edge of colony: little completion for O2, nutrients = exponential growth
Center of colony: depleted O2, accumulates toxins = death phase
Open systems
Culture to which nutrients are continually added and waste products removed
Chemostat: Provides an open system that can maintain continuous growth
Microbial growth factors
Temperature
atmosphere
pH
water availability
Psychrophiles
-5 to 15°C
Found in Arctic and Antarctic regions
Psychrotrophs
15 to 30°C
Spoilage of refrigerated foods
Mesophiles
25 to 45°C
Pathogenic: 35 to 40°C
Thermophiles
45 to 70°C
Common in hot springs and compost heaps
Hyperthermophiles
70° or greater
Usually archaea
Found in hydrothermal vents
Resist denaturing of proteins because of amino sequence stability
Position of bacterial growth O2 requirements (5)
Obligate aerobes: require O2
Facultative aerobes: use O2, but don’t require it
Obligate anaerobes: cannot use O2
Microaerophiles: require small amounts of O2 only
Aerotolerant anaerobes: obligate fermenters, can but don’t use O2
Reactive oxygen species
Harmful by-products of using oxygen in aerobic respiration
Superoxide and hydrogen peroxide
Damages cells
