8.4

TED – How Bacteria ‘Talk”

What is a biofilm? A biofilm is a group of microorganisms in which individual cells stick to one another on a

surface. The biofilm is often embedded within a matrix of extracellular polymers, which can be impenetrable to some antibiotics.

Describe the concept of bacterial conjugation in relation to antibiotic resistance Bacterial conjugation is the non-reciprocal sharing of genetic information between bacteria.

Bacteria that are antibiotic resistant can share this genetic information in the form of a plasmid with other bacteria

Prokaryotes reproduce asexually by binary fission, which gives rise to genetically identical progeny.

But they can also exchange genetic material.

Transfer of genes from one individual to another without sexual reproduction is called horizontal or lateral gene transfer. Along with mutation, this process

generates genetic diversity among prokaryotes.

Bacteria exchange genes by bacterial conjugation.

A projection called the sex pilus initiates contact between cells.

Genetic material then passes from the donor to the recipient through a conjugation tube.

There is no reciprocal transfer of DNA.

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In the recipient cell, the donor DNA lines up with the recipient’s DNA and crossing over occurs.

Genes from the donor are incorporated into the recipient’s genome and are passed on to its progeny.

Many bacteria also have plasmids—small circular DNA molecules that replicate independently. (few dozen genes)

Plasmids often have: Genes for unusual metabolic tasks,

such as breaking down hydrocarbons – oil spills

Genes for antibiotic resistance – R factors – major threat to human health

Plasmids can move between cells during conjugation.

A plasmid has an origin ‘ori’ of DNA replication and genes for other functions

Discovery of antibiotics such as penicillin greatly reduced many lethal infections. But over time, some bacteria acquired mutations that made them resistant. With a selective advantage, as penicillin use spread, so did the resistant bacteria. Scientists designed variants of penicillin; but new strains of resistant bacteria also

develop. This “arms race” still continues.

TED-ED