Bacteriophage Biology

Bacteriophages are...

... viruses which specifically infect bacteria and are completely harmless for humans.

... the most common “life-form” on earth (estimated range: 10^30-10^32 in total).

... highly adaptable. Nature optimized them during evolution, so that for almost every bacterium bacteriophages have been identified.

... ubiquitous in the world. They can be found in nearly every environment, e.g. soil, oceans, deep sea.

Bacteriophages exist…

… in various shapes and morphologies. Most phages (more than 95%) belong to the group of the so-called tailed phages. All these phages are composed of a head, harboring the genetic material and a tail, responsible for the transfer of this material into the host bacterium. These phages are grouped, depending on structure and functionality of their tails, into three families: Siphoviruses (A), Myovirus (B) and Podoviridae (C).

Furthermore there exist other non-tailed morphotypes which are “cubic”, filamentous (D) or even pleomorphic. Characteristic for all phages is the presence of adhesion structures which are necessary for the attachment of the phage to its host, just before the genetic material is injected. These structures are responsible for the specificity towards the bacterial host cells.

Schematic picture:

phages

Viewed through electron microscope:

Phage, viewed through electron microscope

Bacteriophages need…

… bacteria in order to reproduce. Bacteriophages recognize their host bacteria by attaching to specific cell surface receptors. In the next step, they inject their DNA or RNA into the bacterium to reprogram the cell. Now the production of new phage particles starts. Finally, the new phages will be released upon lysis (destruction) of the bacterial cell. The duration of the lytic cycle and the number of phage progeny varies from species to species.

Phages can produce up to several hundred progenies within 20 minutes. Temperate (lysogenic) phages can integrate into the host genome. By this way they are transmitted by the bacteria, when the host cell multiplies. Under conditions unfavorable to the host, these phages may opportunistically switch into the lytic life cycle (below) and by that “survive” to find a new host.

Picture: Schematic lifecycle of a bacteriophage and Hyglos technology summarized in three components (Copyright: Hyglos GmbH)