Aerobic Respiration
Anaerobic Respiration
Chemolithotrophic respiration
Phototrophic metabolism
Binary fission of bacteria
E.coli genome size: 4.6 x 10 6 nucleotides Generation time at optimal conditions: 20min DNA replication rate: 1000nt/s ≈ 1.2 x 10 6 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
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