Do Bacteria Have Sex?

Yes, strange as it seems. Strange because you may recall that bacteria reproduce asexually. In other words, bacteria don’t need sex to reproduce. They just split into two identical daughter cells. This is known as fission, and the result is identical clones.

But–and here’s the interesting part–bacteria also participate in promiscuous and exotic forms of sex. Sex in the sense that genes are exchanged. No bodily fluids, or anatomical maneuvers, just the genes. Bacterial genes are peculiarly mobile.

So What?

1.  Antibiotic resistance and the emergence of superbugs

Pathogens acquire drug-resistance genes from harmless bacteria; sometimes they acquire a suite of genes for resistance to multiple drugs, all “in one stroke.” Instead of passing genes down to children and grandchildren, known as vertical inheritance, bacteria spread their genes horizontally throughout the entire microbial ecosystem. That’s how antibiotic resistance and superbugs spread around the globe so fast. The Pharmaceutical industry can’t keep up.

2.  Genetically modified organisms, GMOs

The genetic engineering techniques that made the biotechnology revolution possible and gave rise to GMOs were copied from bacteria. Bacteria exchange gens with other bacteria via conjugation, transduction, and transformation. The human genetic engineer practices some or all of these techniques for inserting genes into organisms.

3.   The phylogenetic tree of life is contaminated with bacterial genes

Now that scientists can sequence the genomes of more and more organisms, it is apparent that bacteria have been spreading their genes to prokaryotes and eukaryotes throughout the phylogenetic tree of life for millions and millions of years. Therefore the evolutionary tree of life must be revised.

Esther and Joshua Lederberg discovered some of the exotic features of bacterial sex

Esther and Joshua Lederberg collaborated on a remarkable series of discoveries at the University of Wisconsin, from 1947-1959. Together they discovered: 1) F-factor, the fertility plasmid crucial for bacterial conjugation; 2) lambda bacteriophage, the virus that hides out inside of the bacterial genome, and then emerges to damage bacterial cells, much like chicken pox hides out in peripheral nerve cells only to emerge decades later as shingles; 3) replica plating, an elegant technique for selecting mutant colonies of bacteria(see below); and 4) specialized transduction, the capacity of lambda phages to shuttle bacterial genes over to the next infected bacterial cell.

Joshua Lederberg parlayed these discoveries into the 1958 Nobel Prize, which he shared with George Beadle and Edward Tatum. I was surprised to learn that, as a graduate student, Esther Zimmer began her career as a bacterial geneticist in Edward Tatum’s laboratory at  Stanford University, and that George Beadle served as her graduate advisor. The Nobel Prize committee awarded the team of Beadle and Tatum, but only recognized the male half of team Lederberg. The committee ignored Esther’s contributions.

Would Joshua Lederberg have won the Nobel prize, if it hadn’t been for his wife’s contributions? Possibly. Many of his colleagues considered him the most brilliant scientist they had ever known. But some of his colleagues were well aware of how important was Esther’s collaboration. Luca Cavalli-Sforza, the first scientist who collaborated with the Lederbergs in their research on bacterial mating, wrote about Esther Lederberg:

“I know that very few people, if any, have had the benefit of as valuable a co-worker as Joshua has had, and I know that her capacity for observation, organization, imagination, and her sharp mind have been invaluable in this collaboration which has borne so much fruit.”

T. E. Schindler, Ph.D.

I am a former research microbiologist and teacher, currently re-inventing myself as a science writer.

Five years ago, while taking an online course on molecular biology, I heard the wonderful story of how Esther Lederberg invented Replica Plating, an invaluable technique for selecting mutant strains. Like most women in the 1950s, Esther carried a compact makeup case in her purse. One day in 1951, while gazing at a Petri dish speckled with tiny white bacterial colonies, Esther wondered, “What would happen if I pressed my makeup applicator sponge onto the surface of this petri dish and then pressed it onto a fresh plate. Will it replicate the pattern of colonies in exactly the same layout on the new petri dish?” It did, and this was the beginning of her bacterial transfer stamp, known as replica plating, an ingenious technique still used in labs nearly 60 years later!

When I heard this story, told by Eric Lander, MIT professor and former head of the Human Genome Project, I was hooked. I stopped following the course curriculum, and began to dig into the life and career of Esther Lederberg. But apart from obituaries, I quickly learned that most histories of bacterial genetics and the beginnings of molecular biology hardly mentioned Esther Lederberg. If she did receive attention, it was always as the collaborator of her more famous husband, Joshua Lederberg.

This blog will redirect the historical light onto the achievements of Esther Zimmer Lederberg.

By retelling the stories of discovery and highlighting the high regard her colleagues held of her experimental prowess, I hope to balance the record. Many of her closest colleagues and fans refer to Esther Lederberg as “The Mother of Bacterial Genetics.”

Simon, M. 2006. Anecdotes.The Ester M. Zimmer Lederberg Memorial Website.