CELLMOL Bacterial-growth
Chapter 1: Introduction
Exponential Growth
Growth expressed mathematically as 2 raised to 2, progression number of 2.
Relationship between initial and final cell numbers during exponential growth.
Formula for quantifying microbial growth in the presence of specific substances.
Generation time expressed as t over n, where t is the duration of growth and n is the number of generations.
Logarithmic Expression
Formula for calculating the number of generations: 3.3 times log n minus log n sub 0.
Logarithmic expression can be further simplified into log of n equals to log of n sub 0 plus n log 2.
Data Extrapolation from Graph
Example of data extraction from a graph showing population growth.
Doubling time of cells calculated from the graph.
Calculation of generation time based on the data extracted from the graph.
Data Example
Initial number of cells: 5 times 10 to the 7.
Final number of cells: 10 to the 8.
Generation time: 2 hours.
Illustration of initial and final cell numbers on a graph after 2 hours.
Chapter 2: Cell To Cells
Population Growth
It takes about 2 hours for a population to double from 5x10^7 to 10^8.
Formula to compute the number of generations needed for cell doubling: 3.3 times (log n - log n0).
The number of generations required for cell doubling is 1.
Formula to check the generation time: g = t / n.
The slope formula is 0.301n / t or 0.301 / g.
Microbial Growth
Formulas for microbial growth during the exponential phase: 0.301 / g and v = 1 / g.
Specific growth rate (k) and division rate (1 / g) are important growth expressions.
Division rate measures the number of generations per unit of time in an exponentially growing culture.
Microbial Growth Cycle
Phases of microbial growth curve: lag phase, exponential phase, stationary phase, and death phase.
Lag phase: Cells need to adapt to the environment before actively dividing.
Exponential phase: Cells actively divide and double at a specific time interval.
Stationary phase: No net increase in cell number, cells grow in size but do not double.
Exam Focus
Specific growth rate and division rate may not be asked in exams.
Exam questions may involve computing initial/final cell numbers or generation time.
Summary
Understanding population growth, microbial growth phases, and key formulas is crucial in studying cell growth and division.
Chapter 3: Population Of Cells
Growth Phases of Cells
Log phase, exponential phase, stationary phase, and death phase.
In a closed system or batch culture, cells go through these phases.
Lag phase has fewer cells, exponential phase has actively dividing cells, and stationary phase has limited nutrients.
Death phase follows the stationary phase where cells eventually die.
Viable Count in Batch Culture
Viable count measures cells that can still reproduce or multiply.
Cells in the death phase are not viable and cannot multiply or divide metabolically.
Individual cells are hard to quantify in batch culture; focus is on the population of cells.
Cryptic Growth in Stationary Phase
In the stationary phase, there is a balance between cell division and cell death.
Some cells continue to grow while others die, resulting in no net increase in cell number.
This phenomenon is known as cryptic growth.
Continuous Culture
In a continuous culture or chemostat culture, cells can be maintained at the exponential phase.
Factors like population density and growth rate can be controlled by adjusting limiting nutrients and flow rates.
Researchers can manipulate the system by adding or removing nutrients and cells to optimize growth conditions.
Comparison: Batch Culture vs. Continuous Culture
Batch culture involves placing nutrients and observing the products after a certain period.
Continuous culture allows for maintaining cells at specific growth phases by adjusting nutrient concentrations and flow rates.
Chapter 4: Count The Cells
Batch Culture vs. Continuous Culture
In batch culture, nutrients are added only once, while in continuous culture, substrates are added and products are removed in a continuous cycle.
Batch culture involves leaving the nutrient media with microbial cells for a specific period, leading to changes in substrate and waste product concentrations over time.
Continuous culture maintains a balance between substrate and waste product concentrations by adding and removing them continuously.
Effect of Dilution Rate on Bacterial Concentration
Dilution rate, determined by flow rate and volume of the culture vessel, affects bacterial concentration.
High dilution rates can wash out the population as cells struggle to utilize available nutrients.
Too low dilution rates can lead to cell death due to limited nutrients.
Methods for Measuring Microbial Growth
Three main methods: microscopic counts, viable counts, and turbidimetric methods.
Microscopic counts involve counting cells, whether viable or dead, but results can be unreliable due to the expertise required.
Total cell count is an example of a microscopic count method using a counting chamber and specific volume samples for liquid cultures.
Microscopic Count Procedure
Use a microscope and counting chamber to count cells in specific volume samples.
Count cells within small squares and along specific lines while excluding cells on certain lines.
Ensure accuracy by following specific counting guidelines to distinguish microbial cells from debris.
Chapter 5: Number Of Cells
Calculation of Total Cell Count
Formula: Total number of cells x 25 large squares x 50 x 10^3
Question posed on why to multiply by 50 and 10^3
Emphasis on the total cell count as the result
Challenges in Cell Counting
Difficulty in distinguishing between live and dead cells
Motile cells pose a challenge due to movement
Need to immobilize cells for accurate counting
Methods for Cell Counting
Direct count method: Utilizing broth culture and dilution for total cell count
Flow cytometer: Quantifying cells using laser beams and stained cells
Equipment description and process explained
Ability to quantify single viable cells
Application in microbial ecology and advanced research
Viable Cell Count
Definition: Measurement of living cells capable of reproduction
Methods: Spread plate method and pour plate method
Importance of sample dilution for accurate quantification
Differentiation and process of spread plate method described
Chapter 6: Cells Or Colonies
Incubation and Counting Colonies
After incubation, count the number of colonies on the agar surface.
In the pour plate method, add sample, then molten agar, and incubate to see colonies on and within the agar.
Pour plate method allows quantification of more cells compared to spread plate method.
Serial Dilution
Dilute samples to prepare for enumeration.
Perform serial dilution to get different dilution levels for accurate counting.
Transfer samples between tubes to achieve desired dilution levels.
Counting Colonies
Spread plate method used for counting colonies at different dilution levels.
Aim for 150 to 250 colonies for accurate microbial enumeration.
Values outside this range are labeled as "too numerous to count" or "too few to count."
Calculating Colony Forming Units (CFU)
Multiply the number of colonies by the dilution factor to get CFU per ml.
CFU is based on the assumption that one colony comes from one cell.
Great Plate Anomaly
Direct microscopic counts may reveal more organisms than recoverable on plates.
Counts from plate methods may not fully represent the microbial population in nature.
Microorganisms in nature are likely higher than those counted using plate methods due to the exclusion of dead cells.
Chapter 7: Conclusion
Plate Count Method
Counts only viable cells, excluding dead cells.
Different organisms have different nutrient requirements based on their genotype.
Nutrient media in the lab is prepared to support growth of specific organisms.
Some organisms are unculturable in vitro, leading to their exclusion from lab cultures.
Turbidimetric Method
Measures optical density at specific wavelengths to quantify microbial growth.
Turbidity indicates the amount of light transmitted through the sample.
Standard curve