#generation time

Animal Tissue Culture 3

Generation time is defined as:

Generation time, synonymous with doubling time, quantifies interval needed for population to double during exponential phase, reflecting duration of one complete mitotic cycle comprising G1 phase where cells assess nutrient sufficiency and growth factor signaling via Ras-MAPK and PI3K-Akt inducing cyclin D, S phase where DNA polymerase alpha-primase and delta synthesize new genome with fidelity checks, G2 phase where mitotic proteins such as cyclin B and Cdk1 accumulate, and M phase involving spindle formation, chromosome segregation, and cytokinesis. Mathematically derived from growth curves using formula doubling time = t * log2 / log(Nt/N0) where N0 initial cell number and Nt final. Typical values for mammalian continuous lines range 15-24 hours, primary cells longer. Knowledge distinct from attachment time required for spreading, time to death due to stress, or differentiation duration requiring lineage-specific factors. Accurate determination enables feeding schedule optimization, prediction of harvest times for bioprocessing, synchronization of transfection windows when mitosis enhances nuclear entry, and comparison of growth rates under treatment versus control.

Ref: Freshney Ch.13 Generation time one division; Lodish MBoC Ch.13 Cell cycle timing G1 S G2 M doubling time calculation.

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Microbial Physiology

A bacterial culture has a generation time of 30 minutes. How many generations will occur in 3 hours?

Number of generations links time and doubling interval through simple division when cells stay in exponential growth without nutrient limitation. Relation n equals t divided by g, where t total growth period, g generation time. If g 30 minutes equals 0.5 hour, three hours equals 180 minutes. Division yields six generations theoretical. Because population doubles each generation following Nt equals N0 times two to nth power, exponential amplification quickly creates massive biomass from small inoculum. Variation in g with temperature and medium changes actual n; experimentally determined by plating at intervals counting colony forming units. Understanding t over g conversion essential for preparing inocula of defined density, calculating mutation rates via Luria Delbruck fluctuation assuming exponential expansion, and predicting spoilage. In industrial fermentations, extending exponential phase by feeding increases n, while entering stationary truncates. Mathematical simplicity masks underlying complex regulation of DnaA initiation, divisome assembly ensuring constant g during balanced growth phase before substrate exhaustion slows progression.

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Calculating number of generations n=t/g.

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Microbial Physiology

The formula for calculating generation time (g) in bacterial growth is:

Quantitative estimation of bacterial growth uses relationship between elapsed time and number of doublings. Definition generation time g equals total incubation time t divided by number of generations n realized in that interval, g equals t over n. Generation number derived from cell counts using formula n equals log2 Nt over N0 equals log10 Nt minus log10 N0 over 0.301, where N0 initial density, Nt final. This equation derives from geometric progression Nt equals N0 times 2 to n. Therefore knowing t and n yields g, alternatively g predicts expected increase. Reciprocal relationship gives specific growth rate mu equals ln2 over g equals 0.693 over g. Correct dimensionality requires time units. Formulas multiplying N0 and Nt or adding lack theoretical basis. Laboratory application: plot log viable count versus time slope gives mu, intercept N0, g calculated. Accurate derivation essential for designing chemostat dilution rates equal to mu to maintain steady state, evaluating bacteriostatic agents reducing mu, and modeling infection dynamics where generation time dictates time to reach pathogenic threshold load.

Ref: Brock Biology of Microorganisms, 16th ed., Chapter 6: Formula for generation time g=t/n.

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Microbial Physiology

What is the generation time in bacterial growth?

Generation time defines kinetic metric of prokaryotic proliferation, interval required for population to double in cell number during balanced growth. Since bacteria propagate by binary transverse fission, each mother cell splits into two genetically identical daughters after chromosome replication, partition via ParABS, and septal wall formation by divisome. Therefore cell number doubling corresponds to one complete cell cycle. During exponential phase generation time g remains constant, specific growth rate mu equals 0.693 over g. Values vary dramatically: Vibrio natriegens fastest known 10 minutes, Escherichia coli 20 minutes in Luria broth at 37C, Bacilus subtilis 30 minutes, Mycobacterium tuberculosis 18 hours, Mycobacterium leprae days. Medium richness, temperature near optimum, aeration, pH influence g. Measuring g via viable counts plotting log CFU versus time allows calculation of growth yield, prediction of contamination load in food safety, optimization of starter cultures, and assessment of fitness costs associated with antibiotic resistance mutations altering ribosomal or division kinetics.

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Generation time and doubling.

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Microbial Physiology

A bacterial culture is observed for 8 generations in 2 hours. What is the generation time?

Generation time also called doubling time is fundamental growth parameter defined as time interval required for microbial population to double during exponential phase under defined optimal conditions. It is calculated as g equals t divided by n where t is time of exponential growth observed and n is number of generations occurring during that interval measured by viable counts. Dividing total duration by generations yields average time per division cycle encompassing chromosome replication, segregation and septum formation via FtsZ ring. Typical fast-growing Escherichia coli in rich LB medium at 37 degrees Celsius doubles approximately every 20 minutes giving three generations per hour, while obligate slow grower Mycobacterium tuberculosis doubles every 18 to 24 hours reflecting complex lipid-rich wall synthesis and lengthy DNA replication. Knowledge of g permits quantitative prediction of cell density after given time via Nt equals N0 times two to power n, essential for timing subculture to avoid overgrowth, calculating specific growth rate mu equals 0.693 over g, and optimizing inoculum ratios to achieve target biomass for fermentation processes and probiotic production.

Ref: Prescott's Microbiology, 11th ed., Chapter 6: Generation Time Calculation and Bacterial Division Kinetics.

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