Mycobacteria get all the advantages of sex with none of the downsides

Jul 09, 2013

Sexual reproduction is costly to those organisms that depend on it, like humans. For starters, only half of the population can bear offspring and the other half has to work hard to make sure they're included in the future gene pool. The payoff is that sexual reproduction allows the mixing of parental genomes to generate potentially beneficial new combinations of gene variants that had not previously coexisted on the same strand of DNA, or to separate beneficial mutations from detrimental ones.

In contrast, bacteria reproduce by asexual reproduction—this is more efficient than since each individual can reproduce when it's ready, simply by dividing. However, the downside comes when the inevitable accumulation of mutations takes its toll, or changes to the environment make gene combinations less well suited than they had once been. Without an exchange mechanism like that provided by sexual reproduction, the bacteria and their offspring are stuck with the same set of genes, for better or for worse.

However, a new report published July 9 in the open access journal PLOS Biology describes a process by which bacteria can have the best of both worlds. Using a related to the bacterium that causes tuberculosis, Keith Derbyshire, Todd Gray and colleagues, from the Wadsworth Centre in New York, show that a multitude of DNA fragments are simultaneously transferred from a donor to a recipient strain to create new strains that are genetic blends of the parents. The newly-described process, called Distributive Conjugal Transfer, creates patchwork genomes that are different from either parent and different from any siblings. This generates a degree of genome-wide variation similar to that generated in sexual reproduction.

If the new combination of gene variants make the offspring better suited for growth in its current environment, that will rapidly divide asexually, outcompete its parental (or sibling) strains and become established as an emerging strain or species in its own right.

Mechanisms by which DNA can be transferred between bacterial genomes have previously been described, but these have been piecemeal, limiting the potential evolutionary benefit, and requiring successive rounds of transfer to create a genome-wide mosaic. However, Distributive Conjugal Transfer generates mosaic genomes overnight. Thus, scientists may have to re-evaluate the projected time it might take for a new mycobacterial strain to evolve, suggest the authors.

The team also exploited a genomic mapping approach similar to those applied in sexually reproducing organisms to localize the mycobacterial genes that determine mating identity. Of the nearly 7,000 genes in the mycobacterial genome, one region spanning just 6 genes appears to be key in determining whether a mycobacterial strain will be a donor or recipient when it comes to mating. This information may help to predict which other bacterial species might participate in this form of gene transfer, and to identify just how widespread the phenomenon is.

The new study suggests that through Distributive Conjugal Transfer, mycobacteria have found a way to reap the benefits of genomic mixing without the dependence and energy costs associated with sexual reproduction. The findings may also shed light on the origin of related mycobacteria that cause tuberculosis. As more mycobacterial genomes are sequenced, a picture is emerging that Distributive Conjugal Transfer may have shuffled the genomes of environmental mycobacteria to create a strain that was particularly well suited for growth in mammalian lungs. However, whether pathogenic mycobacteria, or other non-pathogenic bacteria, actively participate in Distributive Conjugal Transfer has not yet been addressed.

Explore further: Bacterial DNA may integrate into human genome more readily in tumor tissue

More information: Gray TA, Krywy JA, Harold J, Palumbo MJ, Derbyshire KM (2013) Distributive Conjugal Transfer in Mycobacteria Generates Progeny with Meiotic-Like Genome-Wide Mosaicism, Allowing Mapping of a Mating Identity Locus. PLoS Biol 11(7): e1001602. doi:10.1371/journal.pbio.1001602

Related Stories

Researcher argues that sex reduces genetic variation

Jul 07, 2011

Biology textbooks maintain that the main function of sex is to promote genetic diversity. But Henry Heng, Ph.D., associate professor in WSU's Center for Molecular Medicine and Genetics, says that's not the case.

Recommended for you

Researchers successfully clone adult human stem cells

Apr 18, 2014

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Researchers develop new model of cellular movement

Apr 18, 2014

(Phys.org) —Cell movement plays an important role in a host of biological functions from embryonic development to repairing wounded tissue. It also enables cancer cells to break free from their sites of ...

For resetting circadian rhythms, neural cooperation is key

Apr 17, 2014

Fruit flies are pretty predictable when it comes to scheduling their days, with peaks of activity at dawn and dusk and rest times in between. Now, researchers reporting in the Cell Press journal Cell Reports on April 17th h ...

User comments : 0

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.