Yeast reproduction and growth

The reproduction of yeast can be divided into asexual reproduction and sexual reproduction.

Asexual reproduction includes budding, schizogenesis and asexual spore production, while sexual reproduction mainly produces spores. Beer yeast is asexual reproduction, mainly budding, its reproduction includes the following five stages.

1. The vegetative cells of haploid were propagated by budding.

2. The two vegetative cells combine to form a diploid by nuclear mating.

3. Diploid cells do not immediately carry out nuclear division, but carry out budding propagation and become vegetative cells of diploid.

4. The vegetative cells of diploid transformed into ascospores and the nucleus meiosis into 4 ascospores.

5. The haploid ascospores are used as vegetative cells for budding.

The growth of yeast includes five stages.

1. Delay period. In order to adapt to the new environment, the newly inoculated yeast will appear a stage in which the number of cells does not increase, which is called delay period. In this stage, some active substances in the cell did not reach the minimum concentration required for cell division, so there was a "quiescent phase" before the logarithmic phase. The length of the delay period was related to the condition of the microorganism itself and the nature of the medium.

2. Logarithmic growth period. After the delay period, the yeast adapted to the new environment and entered the logarithmic growth phase of rapid propagation. At this stage, the cells grew at the fastest speed The number of cells increased almost in a straight line.

3. Deceleration period. With the continuous growth and reproduction of cells, there may be some factors, such as the shortage of certain substrates, the continuous accumulation of harmful products, the lack of oxygen supply or the insufficient growth space of yeast, etc. these factors will lead to the slow down of cell reproduction and enter the deceleration period.

4. Stable period. After the deceleration period, the cell growth will stop gradually, the growth curve tends to be stable, and enter the fourth stage, the stable stage. The total number of living cells remains constant during the stable phase, which may be due to the fact that the number of new cells produced by division is equal to that of dead cells, or that the cells only stop dividing but still maintain metabolic activity.

5. Period of death. With the consumption of nutrients and the accumulation of harmful substances, the environmental conditions are deteriorating, resulting in the continuous decline of the number of living cells and the cell growth into the death period.