What is a Bacteriophage?
Raise your hand if you think bacteria are gross! Keep your hand up if you think they are dangerous. Sometimes bacteria get an unfair reputation as nasty germs that make us all sick. Around 5% of bacteria species are actually pathogenic, and many species are harmless or even helpful. Furthermore, bacteria face their own set of enemies out to get them: the bacteriophages. A bacteriophage is a virus (collection of genetic info that uses a host cell for biological tools to help it reproduce) that specifically infects bacteria! Simply put, the phages attach to a bacterial cell, put their DNA in the bacteria, and make the bacteria use its own machinery to build more copies of the phages. Roughly speaking, a phage looks like a lollipop with spider legs at the base of the stick. It has three main parts: the capsid, tail sheath, and tail fibers. The capsid is a case to hold genetic information (DNA or RNA), tail fibers help the virus grab on to the bacteria's cell wall, and the tail sheath helps inject the phage's genetic information into the bacteria.
Bacteriophages can undergo a lytic life cycle (where they replicate and kill the bacteria) or the lysogenic life cycle (where they put their DNA in the bacteria's genome). The four steps of the lytic life cycle are adsorption, replication, assembly, and lysis. Adsorption refers to when the bacteriophage adsorbs, or attaches to the bacteria. The phage will then put its DNA into the bacteria. During replication, the host bacteria cell multiplies the bacteriophage DNA, so there will be genetic instructions to build a whole lot of new phages! Assembly is when the host cell puts together the pieces to form complete bacteriophages. Once the phages are assembled they will break apart the host cell, or lyse it, and get out where they can travel around and infect other bacteria. In the lysogenic cycle, a bacteriophage insert its DNA into a bacterial genome. As the bacteria multiply, they pass down the phage's genetic information also.
Bacteriophages are picky; each kind of bacteriophage usually infects and kills one particular bacterial species. For example, phage T4 infects Escherichia coli. To be fair, some phages are useful as they kill harmful bacteria. Mycobacteriophage DS6A infects Mycobacterium tuberculosis, the bacteria that causes - you guessed it - tuberculosis. Bacteriophages have been used to treat patients with infections caused by bacteria. Research is still being conducted to fully understand how to properly use phage in patients, as well as side effects. Phage therapy may be healthier than antibiotics as they don't disturb the good bacteria that help us stay healthy. Also, the food industry uses phages to kill harmful bacteria in some foods!
