The Virtual Museum of Bacteria

Bacteriophages make bacteria ill

Written by Dr. T. M. Wassenaar Tuesday, 06 January 2009 07:26

Elsewhere in this museum it is described how infectious diseases can be caused by viruses. These minute creatures live parasitic in other cells. Some have viruses have adapted to live in bacterial cells. They are called bacteriophages.

Bacteriophages, viruses that live in bacteria, can have different shapes, and some even resemble little space-shuttles.

• Have a look at bacteriophages.

Bacteriophages are able to attach themselves to (certain types of) bacteria and to inject their genetic material in the bacterial cell. After this happens, their existence becomes more difficult to describe, for only their genetic material (in the form of DNA) exists in the bacterial cell. Then, using the bacterial machinery, the DNA multiplies itself. Eventually from this multiplied genetic information so many new bacteriophages are formed that the cell bursts. The offspring of the bacteriophage has destroyed its bacterial host, and in so doing millions of new bacteriophages are released. These can attach themselves to new bacteria to complete their life cycle.

How do we notice that bacteriophages are present in bacteria? We can see bacteria when they grow, eg. a liquid will become cloudy if there are enough bacteria present (check how our senses can detect bacteria). When we grow bacteria in the laboratory on agar plates, they can completely cover this plate with a confluent layer of growth. If bacteriophages are present in this culture, they will produce holes in this confluent layer. The hole, called a 'plaque', is circular because phages cannot move, so when the originally infected bacterial cell bursts, only its direct neighboring cells become infected. This process produces a round-shaped spread of phages, thus a perfectly round 'plaque'. Check out how plaques attack a Lactococcus culture - the presence of bacteriophages in dairy production plans is a serious problem. Quite a few yoghurt batches have been destroyed by a viral attack.

A liquid that is cloudy from bacteria will become clear again when bacteriophages destroy all cells present. However, bacteriophages do not always kill their host, at least not immediately. Like all infectious organisms, bacteriophages could never make their host extinct, for they are dependent on their host bacteria to survive. This is also true for infectious diseases: they cannot make their target host extinct. See our display on infectious bacterial diseases.

When bacteriophages kill bacteria, can they be used to cure us from pathogenic bacteria? Indeed, phage therapy has been used in the past to cure infectious diseases, especially in Eastern Europe and Russia, and research is continuing. Bacteriophages instead of antibiotic therapy.

A detailed description of bacteriophages can be found here. Bacteriophages are important tools in bacteriological research. They can be used as vehicles to introduce DNA into bacteria. Phages don't mind to take along foreign DNA when they insert their own DNA into a bacterial cells and microbiologists make use of this. However, they make sure to keep the phages under control otherwise all their precious bacterial cultures become infected!

In Nature, bacteriophages sometimes incorporate a bit of DNA from the bacteria they prey on, and transport it into their next hosting cell. That way, bacteriophages can contribute to the evolution of bacteria, which is treated in more detail in another exhibit.

Last Updated on Monday, 07 November 2011 15:57