Mysterious, mutation-generating systems
Wilbanks first encountered the pink berries as a graduate student enrolled in ’s Microbial Diversity course. These spherical aggregates are among the structures bacteria form when genetically similar individuals stick close together and coordinate their activity. The pink berries are populated by a species of bacteria called Thiohalocapsa PSB1, which feeds itself using sulfur and light, plus a relatively small number of other symbiotic bacteria. By working together, these cells create pockets free of oxygen, which could poison them, and acquire the weight necessary to settle safely into their ideal habitat.
Like all organisms, these cooperative microbes risk contracting viruses from their environment. Pink berries and other multicellular bacteria have a heightened need for protection, since — like us — they are composed of genetically similar cells packed tightly together, with no social distancing possible.
“It’s a perfect cocktail for an epidemic to blow through and wipe out everything,” Wilbanks says.
Through her collaborator Blair Paul, assistant scientist at , Wilbanks learned about an unusual genetic mechanism that they found to be abundant within Thiohalocapsa. Known as diversity-generating retroelements (DGRs), this system contains sections of DNA that are transcribed into RNA and back into DNA through an error-prone process, then inserted into a target gene for mutation.
In this way, DGRs introduce lots of new genetic variation, the raw material for adaptation, into specific spots within the genomes. Scientists have found these systems in viruses, bacteria, and other microbes called archaea, yet they don’t fully understand how the microbes use them.