Phases Of Bacterial Growth

Lag Phase
Log Phase
Stationary Phase
Exponential Phase
Decline Phase
Long-Term Stationary Phase

1. STAGES OF BACTERIAL GROWTH M I C R O B I O L O G Y Name - Malay Gorai Stream – B.Pharm 3 rd Year Under The Guidance Of : Prof. Abhijit De BENGAL SCHOOL OF TECHNOLOGY. SUGANDHA, DELHI ROAD, HOOGHLY.

2. Bacterial growth can take place by binary fission during which different phases within which various events take place. Five types of growth curves: 1] Growth cycle 2] Biphasic Growth 3] Maintenance of cells in exponential phase 4] Synchronous Growth 5] Bacterial growth in vivo INTRODUCTION

3. Bacterial growth is regulated by nutritional environment. When suitable environment is available, bacterium is incubated. Its growth leads to increase in number of cells which allow definite course, The growth curve has got five phases: Lag Phase Log Phase (Logarithmic) or exponential phase Stationary Phase Decline or death Phase Long-term Stationary Phase GROWTH CYCLE

4. BACTERIAL GROWTH CURVE LAG PHASE is when bacteria adapt themselves to growing conditions. LOG PHASE or exponential phase is when the bacteria grow very rapidly. STATIONARY PHASE is when nutrients are depleted in the environment. DEATH PHASE is when the bacteria die due to lack of nutrients. LONG-TERM STATIONARY PHASE is when mutation frequency can increase.

5. Bacteria adapt themselves to growth conditions. It is the period where the individual bacteria are maturing and not yet able to divide. During the lag phase of the bacterial growth cycle, synthesis of RNA, enzymes and other molecules occur. Length of this phase depends on the type of bacterial species, culture medium and environmental factors . 1) LAG PHASE (1-4 HOURS)

6. It is the period characterised by cell doubling. The number of new bacteria appearing per unit time is proportional to the present population. If growth is not limited, doubling will continue at a constant rate so both the number of cells and the rate of population increase doubles with each consecutive time period. For this type of exponential growth, plotting the natural logarithm of cell number against time produces a straight line. 2) LOG PHASE OR EXPONENTIAL PHASE (8 HOURS)

7. + The slope of this line is the specific growth rate of the organism, which is a measure of the number of divisions per cell unit time. The actual rate of this depends upon the growth conditions, which affects the frequency of cell division events and the probability of both daughter cells surviving. Exponential growth cannot continue indefinitely, however because the medium is soon depleted of nutrients and enriched with wastes .-

8. This phase occurs due to growth-limiting factors; this is mostly depletion of a nutrient and/or the formation of inhibitory products such as organic acids. Stationary phase results from a situation in which growth rate and death rate have the same values (newly formed cells per unit time = dying cells per unit time). Such an explanation would be in accordance with the observed substrate depletion and also could never explain the rather ‘smooth’ horizontal linear part of the curve during the stationary phase. 3] STATIONARY PHASE (FEW HOURS TO DAYS)

9. Death of cells as a function of time is rather unpredictable and very difficult to explain. There isn’t anymore enough space for the cells. However, under the microscope you will see that there is plenty of water between the cells. Only in agar colony with densely packed cells space is obviously limiting

10. Bacteria runs out of nutrients and die although number of cells remain constant. The decline phase is brought by exhaustion of nutrients, accumulation of toxic products and autolytic enzymes. Sometimes a small number of survivors may persist for month even after death of majority of cells these few surviving cells probably grow at expense of nutrients released. 4] DECLINE PHASE (FEW HOURS TO DAYS)

11. During this phase, cells expressing the growth advantage in stationary phase (GASP) phenotype emerge, GASP mutations confer a competitive ability to cells during stationary phase. Long-term stationary phase cultures are dynamic. The appearance of GASP mutants reflects the fact that stationary-phase cultures are highly dynamic, with new genotypes constantly appearing over them. 5] LONG-TERM STATIONARY PHASE (INDEFINITE TIME PERIOD)

12. Mutation frequency can increase during long term stationary phase as a stress response showing mutations in molecular and genetic methods throughout the chromosome. Incubating bacteria under suboptimal conditions can provide an insight into the stress responses that are active in real-world environments. The process leading to the expression of the GASP phenotype might reflect the mechanisms of generation of genetic diversity used by a wide variety of organisms.

13. Hence, the presentation on Stages of Bacterial Growth was completed by accommodating information from the sources mentioned in the next slide . CONCLUSION

14. a) www.ncbi.com b) www.sciencedirect.com c) Textbook of Microbiology, Stanier. d) Textbook of Microbiology, Ananthanarayan & Paniker’s. e) Textbook of Pharmaceutical Microbiology, Hugo & Russel. f ) Textbook of Microbiology, Pelczer . REFERENCE

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