Bacterial infections have taken over and beaten medicine at an alarming rate and there is no reason we should not expect anything different.
Let’s question and resolve why this occurs in the first place.
Bacterial cells are able to modify themselves much faster than we are able to modify out medication, all thanks to the simple process of gene transfer.
But human cells must be able to perform gene transfer just as well and therefore should be equipped to out-power bacteria cells, should not they?
In order to be able to comprehend why we lose more often than we win against these obnoxious microbes, let’s understand the mechanism behind gene transfer.
There are 2 main types of gene transfer- Horizontal Gene Transfer (HGT) and Vertical Gene Transfer.
Vertical Gene transfer, in simple words is the transmission of DNA of parent to the offspring.
Horizontal Gene Transfer however, is transmission of the genetic material of an organism without reproduction.
It is made possible in large part by the existence of mobile genetic elements, such as plasmids, transposons, and bacteria-infecting viruses (bacteriophages).These elements are transferred between organisms through different mechanisms, which in prokaryotes include transformation, conjugation, and transduction.
Plasmids are extrachromosomal genetic material that are quite common in the Bacterial Realm and conventionally absent in the human body as well as other eukaryotic cells. They are DNA molecules that are independent of the bacterial chromosome- and are hence not completely essential. But they do come with advantages. For instance, R Factors, a type of plasmid, is responsible for antibiotic resistance in the bacteria.
Transposons are genetic materials that have a capability to copy and paste, hence moving through different locations in the genome. Transposons usually don’t advantage their hosts, but sometimes, they have associated genes (like the ones which cause antibiotic resistance). Typically, these resistance genes are carried on transposable elements that have moved into plasmids and are easily transferred from one organism to another.
To add to the problem, Bacteria are constantly being attacked by viruses (these things never seem to get a life, if you know what I mean). These viruses are termed as Bacteriophages (or quite literally, Bacteria Eater). Sometimes Bacteriophages devolve into plasmids, which are then part of the genome of whatever bacterium they have landed in and can be transferred to other bacteria as discussed above.
In transformation, prokaryotes take up free fragments of DNA, often in the form of plasmids, found in their environment. In conjugation, genetic material is exchanged during a temporary union between two cells, which may entail the transfer of a plasmid or transposon. In transduction, DNA is transmitted from one cell to another via a bacteriophage. This newly acquired genetic material is then introduced into the organism’s own DNA material through insertion or recombination. In recombination, the new DNA and the native DNA are homologous (or in simpler words, they share a history in terms of shared ancestry) and are edited and combined. In Insertion, the newly acquired DNA share no history with the native DNA and so, is simply embedded between the Native DNA.
In Unicellular Organisms, HGT is the most dominant form of Gene Transfer- but that’s not good news for us.
So Gene Modification is being carried out at a furious rate in the Bacterial Realm. They are dividing, transferring Plasmids, being attacked by viruses, and having new genes deposited into them by devolved viruses, at a mind blowing rate. Now, there are trillions of bacteria in our body, and even if we suppose a very small rate of genetic modification, more than a million such events are happening every single day! Hence, Bacteria are able to experience Genetic Modification at a much faster rate than we are (Dammit, Lateral Gene Transfer!). And just in case a cell finds a combination that is antibiotic resistant, it can double its population every 20 minutes. At that rate, a single antibiotic-resistant cell can grow into 4,722,336,482,869,645,213,696 cells over the course of a single day!
None of this makes it a joy to lose out to these single cells, but at least you know now what’s giving them the upper hand.
Author: Vedant Munjal and Aastha Munjal Editor: Aastha Munjal Date of Publishing: 24th Apr 2017 Artwork by webmd