Determination of Growth curve of yeast and compute growth rate & growth yield

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Yeast growth rate calculation, yeast population growth, yeast doubling time calculator, how to calculate specific growth rate from growth curve

BACKGROUND

Yeasts are unicellular eukaryotic fungus that have a 5–10 m particle size. They belong to the group of organisms known as ascomycetes, which also includes species from the genera Neurospora and Sordaria. Yeasts have basic nutritional requirements, and they need reduced carbon sources including glucose, sucrose, fructose, and maltose to produce energy.

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The cytoskeleton of the yeast cell, which consists of the three primary components microfilaments, microtubules, and intermediate filaments, as well as the nucleus, endoplasmic reticulum, mitochondrion, Golgi apparatus, and vacuole, is identical to that of the animal cell.

Indefinitely reproducing yeast cells can be either haploids (n) or diploids (2n).

Meiosis, in which one diploid cell goes through premeiotic S-phase and two meiotic divisions to produce four haploid cells enclosed in ascospore walls, or sexual reproduction, in which two haploid cells of opposing mating types (a and ά) communicate with each other using proteins called pheromones, is how the transition between haploid and diploid phases of the life cycle is accomplished.

Growth curve of yeast and compute growth rate & growth yield

The stable haploid cells can also procreate by mitosis.

Studies on the growth of the yeast population necessitate the inoculation of live cells from a pure culture into a sterile medium and the culture’s incubation under ideally controlled environmental conditions. The dynamics of microbial development are seen using a population growth curve, which is created by charting the increase in cell number, metabolic activity, or absorbance against the incubation period. Cells typically multiply quickly.

The curve can be used to define the growth cycle stages and make it easier to assess yeast cell numbers and growth rate as expressed by its generation time, thereby determining how long it takes for a microbial population to double.

Lag phase, log (exponential) phase, stationary phase, and death (decline) phase are the stages of a typical development curve. Each of these phases denotes a specific growth stage that corresponds to a typical physiological shift in the cell culture.

REQUIREMENTS

S. no.
1 Saccharomyces cerevisiae (Baker’s yeast),
2 Glucose,
3 Yeast peptone dextrose agar (YPDA) [Yeast 5 gm, Peptone 10 gm, Dextrose 20 gm, Agar 15 gm, Distilled water 1000 ml, pH 5]
4 Yeast peptone dextrose broth (YPDB) [Yeast 5 gm, Peptone 10 gm, Dextrose 20 gm, Distilled water 1000 ml, pH 5]
5 Test tubes,
6 Inoculation lope,
7 Spectrophotometer,
8 Autoclave,
9 Distilled water,
10 Shaker incubator,
11 Petri dishes.

PROCEDURE

  1. Prepare yeast peptone dextrose agar (YPDA) and yeast peptone dextrose broth (YPDB), autoclave it at 121˚c and 15 psi for 15 min.
  2. One gramme of glucose add to the 10 ml YPD broth along with Saccharomyces cerevisiae, and incubate overnight at shaking condition.
  3. The grown culture was serially diluted with sterile distilled water, use 10-3 and 10-4 dilutions.
  4. 1 ml of aliquots from the selected dilution pour into the petri dish, molten YPD agar poured into the petri plates, swirled clockwise and anticlockwise for uniform layer and allow to solidify, incubate for 24-48 hr.
  5. Well isolated colonies were picked, transferred into the 10 ml YPD broth and incubate at room temperature for 24-48 hr., and use this as stock solution.
  6. The 5 ml stock culture was added to the 200 ml YPD broth, incubate at room temperature on shaking condition.
  7. Take absorbance at 600 nm at every 1 hr of interval for 12-24 hr., starting at zero hr. (0 hr.).
  8. The above observations plot on graph time vs absorbance.
  9. For determination of growth rate and growth yield use plotted graph values, and put them in the below equations

growth yield (G)= t (OD b) – t (OD B)

growth rate (K) = 1/t (OD b) – t (OD B)

Where, OD b = optical density representing a point beginning the doubling of a turbidity during the log phase.

OD B = optical density representing a point ending the doubling of a turbidity during the log phase.

t = corresponding times for OD b and OD B.

growth

CONCLUSION

The growth patterns were determined by measuring the optical density of yeast cells for 12–24 hours, and the growth phases were indicated. the observed value plotted on the graph, and by using this value we calculated the growth rate and growth yield.

Also read:

REFERENCES

  1. Theophilus Abonyi Mensah and Sheila Matilda Ayorkor Tagoe, “Measurement of yeast growth using spectrophotometer”, ResearchGate, 09 June 2019.
  2.  Ivanna Karina Olivares-Marine, Juan Carlos Gonzalez-Hernandez, Carlos Regalado-Gonzalez, Luis Alberto Madrigal-Perez, “Saccharomyces cerevisiae exponential growth kinetics in batch culture to analyze respiratory and fermentative metabolism”, Journal of visualized experiments, 30 September 2018.
  3. Monitoring yeast growth, Neulog.

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FAQs

Doubling time for yeast cells?

Doubling time for wild type of yeast is 90 min at room temperature.

Which phase demonstrates a comparable death rate and reproduction rate?

Since division has completely stopped during the stationary phase, the reproduction rate is equalled by an equivalent mortality rate.

Factors affecting yeast growth?

Temperature, Sugar concentration, pH, Growth factors etc.