Bacteria reproduce by
Binary fissionThe cell doubles in massDNA replicates and the two strands separateThe cell wall and cell membrane begin to invaginateA cross wall formsThe cell separates
Cytokinesis
Is an inward pinching of the cell membrane and cell wall to separate the cell into two genetically identical cells
Doubling Time
The generation (or doubling) time is the interval of time between successive binary fissionsIn pathogens, a shorter doubling time means a shorter incubation period of disease
Growth Curve
Lag phase - Getting used to new environmentLog phase - Exponential growthStationary phase - Birth rate = death rateDeath phase - Waste (typically acid) contaminates the environment and causes death
A Bacterial Growth Curve Illustrates the Dynamics of Growth
During the lag phase, no cell division occurs while bacteria adapt to their new environmentWhen reproductive and death rates equalize, the population enters the stationary phaseThe accumulation of waste products and scarcity of resources causes the population to enter the decline (exponential death) phaseExponential growth of the population occurs during the logarithmic (log) phaseHuman disease symptoms usually develop during the log phaseWhen reproductive and death rates equalize, the population enters the stationary phaseThe accumulation of waste products and scarcity of resources causes the population to enter the decline (exponential death) phase
Endospores
Highly resistant structure formed by Bacillus and Clostridium when nutrient supplies are lowA stress cell undergoes asymmetrical cell division creating a small prespore and a larger mother cell separated by the transverse septum.
Prespore contains
CytoplasmDNADipicolinic acid which stabilizes DNA and proteins
Mother cell
Matures the prespore into and endospore then disintegrates, freeing the spore
Endospore
Resistant to heat and desiccationUndergo very few chemical reactions
Free spore contains
Cell membraneCortexSpore coat - thick peptidoglycanDNAProtein stabilizer - EDTA, similar to Dipicholinic acid
Spore formers
Mostly G+Bacillus anthracis - anthraxClostridium botulinum - botulismClostridium tetanii - tetanusClostridium perfringens - gas gangrene
Spores will survive
2 hours boiling
When will a spore germinate?
When environmental conditions are again favorable, protective layers break down and the spore germinates into a vegetative cell
Growth requirements
TemperatureOxygenpHPressure
Temperature
Each prokaryotic species has an optimal temperature for growth and about a 30? range of acceptable temperatures
Psychrophiles
Grow optimally below 15?C, and make up the largest portion of all prokaryotes on Earth
Thermophiles
Multiply best around 60?C, living in compost heaps and hot springs
Hyperthermophiles
Are Archaea that grow optimally above 80?C, found in seafloor hot-water vents
Mesophiles
Thrive at the medium temperature range of 10? to 45?C, including pathogens that thrive in the human body
Oxygen
Many prokaryotes are obligate aerobes, which require oxygen to grow.Streptococcus
Anaerobes
ClostridiumDo not or cannot use oxygen;
Obligate anaerobes
Are inhibited or killed by oxygen
Facultative prokaryotes
Grow either with oxygen, or in reduced oxygen environments
Thioglycollate broth
Can be used to test an organism?s oxygen sensitivity
Carnophilic bacteria
Require an atmosphere low in oxygen and rich in carbon dioxide
Microphilic bacteria
Likes a small amount of oxygen
pH
The majority of species grow optimally at neutral (~7.0) pH
Acidophiles
Acid-tolerant prokaryotesFor example, those used to turn milk into buttermilk, sour cream, and yogurt
Hydrostatic and Osmotic Pressure
Barophiles can withstand incredibly high hydrostatic pressureFor example, psychrophiles living at the bottom of the ocean
Halophiles
Are salt-tolerant prokaryotesThey can maintain optimal osmotic pressure without suffering from plasmolysis
What materials are used to grow bacteria in the lab?
BrothLiving TissueAgar
Agar
General PurposeEnrichedSelectiveDifferentialSynthetic
General Purpose Growth Medium
A complex medium is a chemical unidentified medium such as a nutrient broth or nutrient agar
Living tissue
Primarily for growing rickettsia
Synthetic medium
In a synthetic medium, the chemical composition of the medium is knownEach amino acid is added individuallyPrimarily for genetic research
Selective medium
Contains ingredients to inhibit growth of certain species and allow the growth of othersSS agar = Salmonella & Shigella
Manitol salt agar
Will only grow staphylococcus. Contains phenol red dye. Staph aureus produces acid and turns dye yellowStaph epidermidis does produce acid, so the dye turns redder.
Differential medium
Contains specific chemical to indicate species that possess or lack a biochemical process
Enriched medium
Some "fastidious" organisms require an enriched medium containing specific nutrientsBloodCooked blood (chocolate)
Can all prokaryotes be cultured?
Many prokaryotes cannot be cultured in a laboratory
Pure culture
A pure culture is a population consisting of only one species of prokaryote
Pour Plate
The pour-plate isolation method allows separation of species through dilution of a sampleMolten agar is poured over a culture in a culture dish
Steak plating
Method for isolating colonies The streak-plate isolation method spreads out individual cells to form discrete colonies of species
Population grows measure 3 ways
Turbidity - cloudinessDirect measurements - actually countIndirect methods - measure dry weight of the cell population to get an indication of the mass. Oxygen uptake in metabolism can also be measured as an indication of metabolic activity.
Standard plate count
In the standard plate count procedure, colonies grow on a plate containing a sample of diluted brothThe number of colonies indicates the original number of viable (living) cells in the broth