Bacterial Growth and Reproduction

Asexual Reproduction - Binary Fission Form of asexual reproduction Results in identical genetic material in both cells Most common form of reproduction in bacteria

Binary Fission DNA Bacteria

Binary Fission Step 1: The bacterial cell elongates.

Binary Fission Step 2: The DNA is replicated.

Binary Fission Step 3: The cell wall and cell membrane begin to form.

Binary Fission Step 4: The cell wall and cell membrane begin to form.

Binary Fission Step 5: Cells separate.

Binary fission creates no genetic variation! It’s just a clone.

Sexual Reproduction & Transfers Bacteria can get variation in their genes by: – sexual reproduction - conjugation – transformation/gene transfer

Sexual Reproduction - Conjugation Not common in bacteria, however conjugation does occur among some bacteria, such as E. coli and Salmonella In conjugation, the donor and recipient bacteria make contact by means of the sex pilus, where plasmids are transferred, giving the recipient an altered set of characteristics Sex Pili *Recall – a plasmid is a loop of DNA that is separate from the main chromosome in the bacteria

Conjugation Step 1: A sex pilis forms.

Conjugation Step 2: The plasmid replicates and travels to the other cell. c

Conjugation Step 3: The cells separate. c

Transformation Bacteria picks up genetic material from the environment in the form of plasmids or fragments of DNA Recall – a plasmid is a loop of DNA that is separate from the main chromosome in the bacteria

Transformation with DNA DNA Bacteria Free-floating DNA

Transformation with DNA The bacterial cell uptakes the DNA.

Transformation with DNA The free-floating DNA and the bacterial DNA combine.

Transformation with Plasmid DNA Bacteria Plasmid

Transformation with Plasmid The free-floating plasmid enters the bacteria.

Recap: Reproduction & Exchange of Genetic Information Type of Reproduction or Exchange of Genetic Information What is it?Creates new bacteria? Creates genetic diversity? Binary FissionAsexual reproduction YesNo genetic diversity Bacterial Conjugations Sharing of a plasmid from one bacterium to another NoYes, creates genetic diversity Bacterial Transformations Picking up a plasmid from the environment NoYes, creates genetic diversity

Unfavourable Conditions During unfavourable conditions, some bacteria survive by forming dormant or resting cells, called endospores. Endospores are resistant to heat and other extreme conditions, and cannot be easily destroyed When suitable conditions return, the endospore sprouts and an active bacterium emerges. A thickened cell wall forms around the genetic material and cytoplasm. The remainder of the original cells eventually disintegrates. Endospores

Growth Curves Generation Time: The time required for a cell to divide or a population to double Most bacteria have a doubling time of 1-3 hours, although some may be greater than 24 hours Example: E. coli has a doubling time of 20 minutes Bacterial division occurs according to a logarithmic progression (two cells, four cells, eight cells, etc.).

Growth Phases During the lag phase, there is little or no change in the number of cells, but metabolic activity is high. – Bacteria are adjusting to their new surroundings. During the exponential growth phase, the bacteria multiply at the fastest rate possible under the conditions provided. During the stationary phase, there is equilibrium (balance) between cell division and death. – Nutrients are exhausted and waste products build up During the death phase, the number of deaths exceeds the number of new cells formed.