Bacterial Growth and Reproduction

Bacterial growth curve

There are 4 key phases in bacterial growth

• lag phase
  • an increase in metabolic activity with no increase in cell count
• log (exponential) phase
  • a rapid expansion of cell count
  • (beta-lactam) antibiotics act during that phase
• stationary phase
  • a slowing of cell count expansion secondary to reduced nutrients
  • bacteria begin to form spores
• death phase
  • consuption of resources and build up of waste results in bacterial death

Transformation?

Ability to take up naked DNA (i.e., from cell lysis) from environment (also known as “competence” ). A feature of many bacteria, especially S. pneumoniae, H. influenzae type B, and Neisseria ( SHiN ) . Any DNA can be used. Adding deoxyribonuclease to environment will degrade naked DNA in medium and no transformation will be seen.

Q. What do you mean by conjugation?

F+ x F-

F+ plasmid contains genes required for sex pilus and conjugation. Bacteria without this plasmid are termed F-. Plasmid (dsDNA) is replicated and transferred through pilus from F+ cell. No transfer of chromosomal genes.

HFr x F-

F+ plasmid can become incorporated into bacterial chromosomal DNA, termed high-frequency recombination ( Hfr) cell . Replication of incorporated plasmid DNA may include some flanking chromosomal DNA. Transfer of plasmid and chromosomal genes.

Q. Define Transposition?

Segment of DNA that can ” jump” (excision and reintegration) from one location to another, can transfer genes from plasmid to chromosome and vice versa. When excision occurs, may include some flanking chromosomal DNA, which can be incorporated into a plasmid and transferred to another bacterium.

Q. Enumerates types of Transduction?

Generalized: A “packaging” event. Lytic phage infects bacterium, leading to cleavage of bacterial DNA. Parts of bacterial chromosomal DNA may become packaged in viral capsid. Phage infects another bacterium, transferring these genes.