Jessica Snyder Sachs

To work in Abigail Salyers’ laboratory at the University of Illinois, is to play matchmaker to some unlikely couples. Standing at her laboratory bench, PhD student Kaja Malanowska lifts the cover from a petri dish to pick up a half a billion or so Escherichia coli bacteria with the tip of a sterile needle. She adds them to a tube containing about as many Bacteroides thetaiotaomicron floating in a tiny puddle of antibiotic-laced broth. Finally, Malanowska transfers the tube to an incubator set at 98.6° F – human body temperature – where she will leave them to co-mingle for the night. What Malanowska will find in the morning is no secret to her mentor. “In the bacterial world’s version of casual sex, E. coli and B. theta will swap a few genes,” explains Salyers For decades, microbiologists have known that bacteria employ a variety of methods to share genes between species, with each gene or group of genes spelling out the DNA instructions for a potentially useful trait. What initially took Salyers by surprise was