Microbial dynamics

Define microbial dynamics

Microbial dynamics: Study microbial population changes and interactions including how microbes grow, reproduce,die and interact with each other and their environment over time and space.

Meaning of growth

Growth

• Def: orderly increase in sum of all components of organism

• Cell x is consequences of growth.

• In unicellular organisms growth leads to increase number of individuals making population or culture

Describe bacterial reproduction by binary fission (mitosis)

Binary fission steps

1. Nuclear material divides

2. Transverse septum originates from plasma memb and cell wall divides cell into 2 parts

3. 2 daughter cells receive identical set of chromosome

4. Daughter cells separate and may be arranged singly, pair, clumps or chains

Growth curve : Def , the 4 growth phases and total count vs viable count

• Growth curve: Growth curve indicates multiplication and death of bacteria

• Bacteria passes through 4 phases : Lag, Log, Max stationary , Decline/ Death phase

• Bacterial count is used in examination of water and milk

• Total count vs viable count…

1. Total count = Living + Dead bacteria

2. Viable count = Living only

Growth phase : Lag Phase features

• Increase in cell size but not multiplication

• Enzymes formed and accumulate until present in concentration that permits growth to start

• Antibiotic have little effect at this stage (it targets enzyme not growth)

Growth phase : Logarithmic (Log) Phase features

• Cells multiply at max rate by binary fission division

• Continues till…

1. 1 or more nutrient in medium become exhausted

2. Toxic metabolic products accumulate and inhibit growth

• Nutrient oxygen becomes limited for aerobic organisms

• Antibiotics act better at this stage → kill bacteria, stop bacteria x

Growth phase : Maximal stationary phase features

• Due to nutrient exhaustion or toxic products accumulation death of bacteria starts and growth cease completely

• Count remains stationary as multiplication rate = death rate

• Importance: Production of exotoxins (alive bacteria), antibiotics, metachromatic granules and spore formation take place in this phase

Growth phase : Decline/Death phase features

• In this phase progressive cell death

• However some living bacteria use product breakdown of dead bacteria as nutrient and remain

Maintenance of cells in the exponential phase

Cells can be maintained in exponential phase by transferring them repeatedly into fresh medium of identical composition while they are still growing exponentially → called continuous culture