Lecture 7: Growth And Control Of Growth

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BINARY FISSION

Back 1

-asexual reproduction
-genetically identical offspring
-allows for exponential growth

Front 2

Generation (doubling time)

Back 2

-the amount of time it takes bacteria every time it divides and reproduces
-varies from species to species

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BIOFILM and its importance

Back 3

-polymer encased microbial community
-bacteria grows on a surface
-sense and responds to environmental change, interacts with organisms in complex communities

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PURE CULTURE

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-single species from once cell
-used in laboratories
-can behave differently than in natural habitat
-only 1% have been cultured

Front 5

Bacterial Growth Curve

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-applies to liquid cultures
-lag phase
-exponential (log) phase
-stationary phase
-death phase
-phase of prolonged decline

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Lag Phase

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-not much growth
-starting, small population
-building macromolecules needed to produce more
-length depends on starting pop & richness of nutrients

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Exponential (log) Phase

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-population doubles every generation
-synthesis of 1* metabolites (required for growth)

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Stationary Phase

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-growth is 0
-# new cells = # of dying cells
- 2* metabolites (toxins, etc)

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Death Phase

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-# new cells < # dying cells
-fairly constant rate of decline

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Phase of Prolonged Decline

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-remaining bacteria are the most "fit"
-quick evolution of population

Front 11

What is optimal growth temperature?

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-temperature at which organism multiplies most rapidly
-enzymes determine optimal temp

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Does freezing or chilling food kill most bacteria? Why?

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-No
-Enzymes work better at higher temperatures
-cold slows them down
-membrane gels, growth slows or doesn't occur

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Does high heat kill most bacteria? Why?

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-yes
-high heat denatures the enzymes
-causes cell to collapse, thermal lysis

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PSYCHROPHILES

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-cold lovers
-10*C

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PSYCHROTROPHS

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-can grow in cold
-25*C, room temp

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MESOPHILES

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-warm lovers
-37*C, body temp

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THERMOPHILES

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-heat lovers
-60-70*C

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HYPERTHERMOPHILES

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-really heat lovers
-90-100*C
-very resistant to denaturing

Front 19

How do prokaryotes survive in extreme pH environments?

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-enzymes adapted to survive
-can control # p+ in cells

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How do some bacteria prevent plasmolysis in hypertonic environments?

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-pump ions so cell concentration is similar to environment, prevent osmosis

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How can oxygen be toxic to a cell?

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-oxygen oxidizes cells, takes e-
-anaerobic microbes cannot produce enzymes to protect from oxidation
-(superoxide dismutase, catalase)

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Describe the roles of superoxide dismutase and catalase in oxygen utilization and/or intolerance

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-protection from oxidation if have enzymes
-superoxide dismutase catalyzes superoxide into hydrogen peroxide and oxygen
-catalase breaks hydrogen peroxide into water and oxygen

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Obligate aerobes

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-need oxygen to survive
-& to produce energy in ETC
-have both enzymes

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Obligate anaerobes

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-No oxygen, anaerobic respiration
-DON'T have the enzymes

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Facultative anaerobes

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-can live w/out oxygen by doing fermentation
-prefers oxygen
-have both enzymes

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Microaerophile

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-small amount of oxygen (2-10%)
-produces catalase sometimes
-cant survive in too little or too much oxygen

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Aerotolerant aerophiles

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-(obligate fermenters)
-only do fermentation
-can survive in oxygen

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Neutrophiles

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- pH 5-8 (body pH)

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acidophiles

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- pH <5

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alkalophiles

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- pH > 8

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facultative

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-optional
-can have, but not neccesary

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Obligate

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-need to survive

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Major nutritional modes

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photoautotrophs- photosynthesis
photoheterotrophs- only prokaryotes
chemoautotrophs- only prokaryotes
chemoheterotrophs- us

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sterilization

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-highest level of bacterial control
-kill all microorganisms, bacteria, viruses, endospores
-heat, chemicals, irradiation, filtration

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Disinfection

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-gets rid of things that cause pathogens, things that cause disease
-disinfectant- surfaces
ex. bleach, lysol
-antiseptic- skin
ex. hydrogen peroxide, isopropyl alcohol

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Pasteurization

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-brief heat treatment
-reduce bacteria that would spoil food or containers

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Physical methods of microbial growth control and applications

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HEAT
*moist- boiling- low tech inexpensive destroys most organisms and viruses, doesn't destroy endospores
-pasteurization- significant reduces organisms, increase shelf life
-pressurized steam-
autoclave
*Dry- not as effective, requires longer times and higher temps-incineration- burning
-membrane filtration- fine filter traps bacteria and viruses
liquid or air
-radiation- zap w/ UV light- used for food
ionizing or non
-pressure- denatures proteins, uses less heat

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Chemical methods of microbial growth control and applications

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-(antiseptics/disinfectants)
-germicidal chemicals
-reacts with vital cell sites
-liquids- alcohol
-gas- ozone

Front 39

Describe how food products and other products can be preserved by preventing the growth of microbes

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-breads, cheeses, juices preserved by adding weak organic acids
-meats processed with nitrite or nitrate inhibit growth of endospores
-refrigeration inhibits growth by slowing or stopping enzyme reaction
-freezing stops microbial growth but some can survive and spoil once thawed
-salting and drying decreases availability of water in food below limits required for growth of most microbes, high concentration causes plasmolysis
-adding salt or sugar dehydrates cells

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plasmolysis

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shrinking of the cytoplasm of a plant cell due to the diffusion of water out of the cell into a hypertonic solution