Photosynthetic bacteria give biologists a cool new tool

Photosynthetic bacteria that have lived on Earth for 2.7 billion years are the source of a new and valuable biological regulatory tool being developed by Rice University bioengineers.

Synechocystis bacteria produce a protein pathway that senses the presence of UV-violet light and activates a motor protein that moves the single-cell organism into safer surroundings.

The pathway responds quickly to UV-violet light, a narrow band in the spectrum that includes long ultraviolet and short violet wavelengths, and is blind to all others. That makes it a perfect addition to the growing optogenetic suite of reversible photoreceptors being developed by researchers in the lab of Rice synthetic biologist Jeffrey Tabor.

Optogenetics is a fairly new discipline in which light-activated, genetically encoded photoreceptors are used to sense or control molecular biological processes like the expression of desired proteins. Because light is easy to direct and control, photoreceptors are simpler to use than tools that respond to chemical prompts.

The Rice researchers turned the photosynthetic bacterial proteins into photoreversible, transcriptional regulators and installed them in Escherichia coli bacterial for lab testing. They reported exploiting them to program gene-expression signals "with high predictability."

The protein pathway known as UirS-UirR is the only optogenetic tool that responds exclusively to UV-violet light and gives biologists the ability to program circuits with light-activated proteins that won't interfere with each other, Tabor said. "Biological systems are regulated by numerous interacting genes, and multiple optogenetic tools that don't optically cross-react are needed to study these networks," he said.