Lysogeny in Temperate Bacteriophages
Lysogeny and lysis are the two main replication methods used by bacteriophages. Phages are distinctively split depending on the replication process they use. The identification of which bacteriophage belongs to which group, is crucial.
Another replication state which is less mentioned is known as the pseudolysogeny. This is when a bacteriophage finds itself in a stalled state. It is unable to replicate or choose to become a prophage due to the lack of nutrients in its environment, resulting in an unstable and inactive state.
Virulent phages, that undergo the lytic cycle can be seen as special ops soldiers, whilst temperate phages, which undergo lysogeny, are sleeper spies. The differentiation of the two plays a critical role in understanding the motives and approaches that bacteriophages would take on to reach their ultimate goal.
Whereas the lytic cycle seems to have a clear direction, lysogeny is seen to be complex, with many avenues and hidden agendas which will be looked into in this article.
Location of Lysogenic Bacteriophages in Bacterium
Temperate phages undergoing lysogeny are also not all alike, with certain characteristics that set them apart from other lysogenic bacteriophages. One of the main differentiates between lysogenic phages is their physical positioning inside a bacterium. While some embed and integrate into the bacterium genetic material, also known as bacteriophage lambda and resulting in a prophage, others remain free-flowing in the bacterium’s cytoplasm as a low copy plasmid, such as the phage P1 and Vibrio VP882.
Choice between Lysis or Lysogeny
It is important to note that although some bacteriophages have the capability of choosing whether to be virulent or temperate, others lack that ability. Phages T2 and T4 have been classified as strictly virulent phages, therefore following the lytic cycle.
Bacteriophages which have the capability to choose between lysogeny and lysis, make such as decision due to certain factors;
1. State of virulence
A temperate phage may decide to undergo lysis which is referred to as phage induction. Such a decision can be influenced by the following;
- Physical factors:
UV radiation, ionizing radiation, high temperature, high hydrostatic pressure, ultrasound and drying.
- Chemical factors
Mustard gas, halogen-substituted analogues of uracil, sulfathiazole, sulfuric, glutathione, hydrogen sulphide and nitrous acids.
- Biological factors
Enzymes, bacteriocins, antibiotics and others.
A recent study by scientists from UC San Diego, has shown that certain food products can induce lysis in a prophage within a bacterium. Products tested in vitro (laboratory conditions), which showed results include;
- Complex stevia, a sugar substitute which is widely used, resulted in prophage induction in Bacteroides thetaiotaomicron.
- Bearberry, propolis and aspartame, showing the best outcome on prophages found inside Enterococcus faecalis.
Stevia, grapefruit seed extract and toothpaste induced prophages in Staphylococcus aureus.
- Other products showed a reduction in phage particles within all the four bacteria that were tested. Such products were; rhubarb, fernet, arabica coffee and oregano.
2. Status of prophage
When a prophage is integrated in the genetic makeup of the bacterium, only part of its genes are active, whilst those responsible for reproduction are blocked.
3. Obligatory virulent state
The loss of the ability to choose the lysogenic state due to either damage or deletion at the c1 locus in the bacteriophage.
4. Obligatory integrated state
The loss of the ability to choose the lytic cycle due to the absence of the cro gene, leading to just the state of lysogeny.
5. State of a plasmid
Due to damage or deletion, the phage is no longer able to form a protein envelope, but retains the replication ability.
Others factors have been observed with the bacteriophage lambda;
Phage fragments knows as cos sites, which are responsible for the packaging of the molecule, with fragments of foreign DNA.
7. A chimeric infectious agent
DNA of the polyoma virus introduced into the phage lambda DNA, resulted in a chimera virus which triggered lysis of the bacteria.
To date, the widespread emergency towards antibiotic-resistant bacteria is a global problem for the treatment of infectious diseases. The presence of a prophage in a bacterial DNA plays a large role in the development of this ability in bacteria. It has been observed that bacteria show the ability to multiply virulently, increase resistance towards antibiotic treatment and significantly reduce the immunity of an infected organism.
Taking into consideration the condition of prophage induction (the triggering of lysis due to unfavorable conditions), it is most likely that a prophage induction may occur when the bacterial host is exposed to unfavorable conditions and/or is in a threating environment. Therefore, exposing bacteria to natural antibacterial products, resulting in the bacterial cells to face an unfavorable environment, may provoke a prophage within the bacterium to undergo prophage induction.
In addition to natural food products that are known to have antibacterial properties, the effects of intermittent fasting may possibly create an unfavorable and threatening environment for bacteria.
All these observations show a variety of directions that may be looked into in the near future when searching for solutions towards antibiotic resistance. With a possibility that at least in some cases, nutrition and a change in lifestyle may be the key trigger towards prophage induction from within (given that the bacteria has a prophage), and to activate a defense system against bacterial infection, especially in cases of chronic infections.
Sherwood R.Casjens and Roger W.Hendrix. Published in ScienceDirect 2015 | DOI: 10.1016/j.virol.2015.02.010
Yu.A. Rebolskaya, E.A. Vasenko, S.V. Melnik, D. X. Sabirov and E.V. Sarygina. Published in ScienceForum 2018
Stefan Jordan, Navpreet Tung, Maria Casanova-Acebes, Christie Chang, Claudia Cantoni, Dachuan Zhang, Theresa H. Wirtz, Shruti Naik, Samuel A. Rose, Chad N. Brocker, Anastasiia Gainullina, Daniel Hornburg, Sam Horng, Barbara B. Maier, Paolo Cravedi, Derek LeRoith, Frank J. Gonzalez, Felix Meissner, Jordi Ochando, Adeeb Rahman, Jerry E. Chipuk, Maxim N. Artyomov, Paul S. Frenette, Laura Piccio, Marie-Luise Berres, Emily J. Gallagher and Miriam Merad. Published in Cell 2019 | DOI: 10.1016/j.cell.2019.07.050
More questions on the topic:
- Would the intake (in vivo) of natural antibacterial food products such as; garlic, onions, horseradish, vitamin C, honey, cinnamon, and apple cider vinegar, cause a strong enough discomfort to persistent bacterial cells, in order to trigger a lytic cycle from a prophage within?
- Is there any connection between the deprival of nutrients by the bacteria during intermittent fasting and the triggering of a prophage induction from within, in order to survive, being currently observed as an immune response?