Transcript Aerobic Respiration

Aerobic Respiration
Anaerobic Respiration
Chemolithotrophic respiration
Phototrophic metabolism
Binary fission of bacteria
• E.coli genome size: 4.6 x 106 nucleotides
• Generation time at optimal conditions:
20min
• DNA replication rate: 1000nt/s ≈ 1.2 x 106
nt/20min
• About 25% of genome can be replicated in
one generation time
Population growth
• Growth rate: change of cell number per unit time
• When growth is unlimited, growth rate is low at first,
increases logarithmically
• Plotted on semi-log paper, growth is a straight line
• Generation time: time required for one cell to grow into
two cells (varies from several minutes to months)
• Specific growth: instantaneous change in relative cell
numbers (µ)
• µ = ln(2)/generation time
Logarithmic growth
Batch growth stages
Lag and Exponential
• Lag phase
– Longer when inoculum conditions differed
– Some inocula may require synthesis
– Apparent lag caused by partial death of inoculum
• Exponential phase
– Logarithm of cell numbers increases linearly
– Specific growth rate is constant—characteristic of
growth conditions
– Cell physiology is constant—best source for
biochemical studies is late exponential phase
Stationary and Death
• Stationary phase
– Culture is eventually limited by substrate or nutrient exhaustion or
product accumulation
– Metabolism changes to accommodate the limitation
– Lysis of some cells may lead to growth in others
– Cell increase equals decrease (cryptic growth)
• Death phase
– Death is generally logarithmic, but slower than growth
– Sometimes death rate changes after hours or days
Calculating specific growth rate
Counting Chamber
Counting cells in a chamber
Quantitative plating
Pour plates
Pour-plating techniques
Optical density
Continuous culture
• Chemostat permits independent control of
population density and growth rate
• Dilution rate
• Concentration of limiting substrate
• Cultures can be maintained in exponential
growth rate for a long time
Temperature effects on growth
Temperature groups
Temperature groups
• Psychrophile
– maximum < 20 C
– Optimum 15 C
• Mesophile
– maximum > 20 C
– optimum < 45 C
• Thermophile
– optimum 45 to 70 C
•
Hyperthermophile
– optimum > 80 C
– highest known maximum about 113° C (Pyrolobus fumarii)
Growth in hot springs
Deep-sea hydrothermal systems
Effect of pH on growth
Effect of salinity on growth
Growth with low water activity
• Terms reflecting tolerance of low water activity
– Xerotolerant
– Xerophilic
• Terms relating to tolerance of salt
– Halotolerant
– Halophilic
• Slightly (~0.5 M)
• Moderately (0.5 to 1.5 M)
• Extremely (> 1.5 M)
Compatible Solutes
Effect of Oxygen on Growth
Protection from Oxygen
Demonstration of catalase