Recently, it has been discovered that mycobacteria, have the “best of both worlds” when it comes to reproduction. They use a type of DNA transfer, called Distributive Conjugal Transfer, to swap genes with other mycobacteria. After the genome is thoroughly mixed, the bacteria is able to replicate asexually. Because these organisms are able to obtain a “genetic blend” of DNA from parent bacteria (a type of quasi-sexual reproduction), and also replicate individually, it seems that they are reaping the benefits from both types of reproduction, with none of the disadvantages.
Sexual reproduction is costly for organisms. Only half of the population can produce offspring; the other half must fight it out to ensure their genes are passed on to the next generation. The benefit of this replication is the genetic variance; the mixing of two genomes allows the offspring to be better suited for survival. The new combinations could be more favorable to environmental conditions, and also may help separate advantageous mutations from harmful ones.
In contrast, asexual reproduction is replication that involves only one individual, simply through division. This is the common type of reproduction in bacteria, and is a major contributor in why bacteria have such large population sizes. The downfall of asexual reproduction is that the organism is “stuck with what they get;” offspring will keep the same mutations the parent had.
Mycobacteria have found a way to do both. Through Distributive Conjugal Transfer, they are able to create mixed genomes for future generations, and after - if the genes make the bacteria “more fit” for their environment - are able to reproduce asexually, ensuring every bacterium will produce genetically dissimilar offspring. The diversity of the genome, caused by Distributive Conjugal Transfer, allows the bacteria to adapt better to their environment, remove potential chances for harmful mutations to be passed on, and ultimately helps the population flourish through their own small-scale natural selection.
Distributive Conjugal Transfer is not unlike other types of transfer that have been studied in the past. Conjugation (via sex pili) is, in fact, similar to this process. However, DCT has been found to be much more efficient in gene swapping. To “mix” a genome, which can be done in only one night with DCT, may take multiple rounds of transfer through other processes, like conjugation.
Distributive Conjugal Transfer moves gene fragments from a donor bacteria to a receiving bacteria. The genes that code for whether a bacterium will be a “donor” or a “receiver” is only 6 genes long, out of about 7,000 in a microbial genome. This specifically mapped site will make it easier in the future to distinguish what other bacteria have the ability to participate in this type of genomic transfer.
Summary written by: Laura Burbach