Sticky when wet

Making glue that works underwater is a sticky business. Now scientists have engineered bacteria to efficiently produce proteins that mussels use to cling to rocks in the churning surf. The technique could lower the cost of mussel adhesive proteins, or MAPs, and perhaps make them economical for uses in medicine and biological research.

“The possibility to use MAPs in lots of medical areas, including antibiotic coatings on cardiac stents and other medical implant devices, has been suggested by lots of scientists,” says Hyung Joon Cha, leader of the research at Pohang University of Science and Technology in Pohang, South Korea. Mussel adhesive could bind antibiotic compounds to the stents to prevent infection, a major concern for implant procedures. The protein, a stronger adhesive than epoxy, could also bond broken teeth or bones, or hold together cells or tissues for scientific research.

“The fact that mussels have evolved and adapted their adhesion under wet conditions to work on almost any surface makes them interesting for commercial uses,” comments Herbert Waite, a biochemist specializing in biological adhesion at the University of California, Santa Barbara.

Mussel adhesive protein is available commercially from BD Biosciences, a New Jersey–based medical technology company, but each gram of the protein requires processing about 10,000 mussels and costs around $100,000.

“It’s awfully work-intensive because you can’t just throw the mussels into a blender,” Waite says. “You have to dissect them very carefully and cut the foot out and then do the extraction on that foot,” the tonguelike, muscular appendage that mussels use to hold on to underwater surfaces.

Cha’s team previously engineered E. coli bacteria to produce a variant of the adhesive called fp-151, but production was inefficient. In the new work, the scientists added a hemoglobin gene from another family of bacteria to the E. coli. This gene boosted the microbes’ ability to use oxygen, which is often in short supply in the large stainless steel tanks in which the bacteria are grown. Improved oxygen use almost doubled the protein output, the team reports in the June 6 Biotechnology Progress.

The scientists have produced only small quantities in the lab, but Cha says that scaling up the process should be cheap enough to make the protein economical for medical uses. Previous experiments have shown that mussel proteins are not toxic and do not provoke dangerous immune reactions in people. “The safety on these looks really good,” Waite says.

The chemical adhesive cyanoacrylate, sold as Superglue, also works on wet surfaces and has been used for some medical purposes, but it is “used with a great deal of reticence and usually as the last resort” because of toxicity issues, Waite says.