And Now, Something Completely Different

The original recreational sex

Mark Ridley, the British zoologist who writes popular books about evolution, wrote that bacteria practice “the original recreational sex.” Among millennial humans, recreational sex might mean casual hookups, not intended for reproduction. But for bacteria, “sex is interestingly different from the kind that we and all complex life forms use.”

Olivia Judson, who has popularized the exotic varieties of sex in the natural world, imagined the bacterial point of view:

“For us bacteria, reproduction is reproduction and sex is sex. Unlike you ‘higher’ creatures, we’re not so vulgar as to do both at once. For us bacteria, reproduction is asexual: we simply divide into two genetically identical cells. This way, sex—by which I mean the acquisition of extra genes—is something that we reap the benefits of during our lives. If humans could do this, which they can’t, it would be like suddenly adding a few genes for longer legs or bluer eyes.”

How do bacteria “do it?”

Bacteria have three distinct was of “doing it:” 1. Transformation, 2. Transduction. 3. Conjugation. Judson’s imaginary spokesman for the bacterial domain continues,

So, how we do it? We have several ways. We pick up DNA that’s loose in the environment [transformation] .We gather DNA from passing viruses  [transduction].. . . We also indulge in bestiality, getting genes from bacteria of other species [conjugation]

The three types of gene transfer in bacteria

Conjugation: bacteria hook up

Although complicated, conjugation is somewhat similar to the sex of higher organisms, in that it involves males (DNA donors) and females (DNA recipients). But unlike the mutual transfer of genes between both parents of higher organisms, in the bacterial domain genetic transfer is one-way, only from male to female. Additionally, only a portion of the donor genome gets transferred. Another peculiar aspect, discovered by Esther Lederberg in 1950, is the F plasmid (F for fertility). Bacterial cells that possess the F plasmid (a circlet of DNA separate from the main bacterial chromosome) are donors (F+) capable of transferring genes to F- recipient cells. F+ donors can also transfer the F plasmid to F- recipients, transforming them to F+, sort of like “infective fertility,” the odd, bacterial twist on STDs!

Conjugation drives antibiotic resistance

During the late 1950s, in postwar Japan, clinical researchers discovered that the bacterial pathogens causing dysentery (Shigella) had become resistant to four different antibiotics through the process of conjugation. Resident E. coli bacteria—normal harmless flora of Japanese patients—had transferred resistant genes, all in step, to the pathogens. This was the first indication that bacterial sex was responsible for the rapid emergence of superbugs. Notably, the transfer of genes occurred between two different speciesE. coli to Shigella—sort of bacterial bestiality!

The three processes, transformation, transduction and conjugation, are collectively known as Horizontal Gene Transfer, HGT. Among higher organisms, the direction of genetic transfer is vertical since traits are passed on to offspring down through the generations.

Bacterial sex effectively spreads genes horizontally among different species, throughout the bacterial ecosystem.

Bacteria Are Very, Very Different

Bacterial sex, discovered in the 1940s and 50s, confirmed that bacteria were not just very small cells, but represented a completely different kind of cell. The early research began in 1946 when Joshua Lederberg and Edward Tatum first discovered bacterial conjugation. Joshua and Esther Lederberg, and their colleagues Cavalli and Hayes, continued to uncover the peculiarities of bacterial sex in the early 1950s. But Joshua Lederberg viewed bacterial conjugation as similar to the conventional sex of higher organisms. Then, during  the mid-50s, the French team of  Wollman and Jacob clarified the mechanism of bacterial mating and revealed a completely different kind of sexual process.

Mark Ridley. 2001. The Cooperative Gene. How Mendel’s Demon Explains the Evolution of Complex Beings. The Free Press, New York.

Judson, Olivia. 2002. Dr. Tatiana’s Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex. Henry Holt and Co.. Kindle Edition.

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