COURTESY MAYA BAR DOLEVThe paper
M. Bar Dolev et al., “Putting life on ice: Bacteria that bind to frozen water,” J R Soc Interface, 13:20160210, 2016.
In 1999, Jack Gilbert set off for Antarctica looking for a natural antifreeze. Out among the sea ice, the microbial ecologist, now based at Argonne National Laboratory, found a bacterial antifreeze protein (AFP) called MpIBP that was hundreds of times larger than other known AFPs. It was an enigma, he says. “For years, I’ve been telling people we don’t really know what this protein does.”
Fishing for ice
Scientists now have a handle on its function. Ido Braslavsky of the Hebrew University of Jerusalem and colleagues placed Marinomonas primoryensis, which produces MpIBP, into a microfluidic flow chamber with a copper wire kept at sub-zero temps and embedded in the middle. Micrographs of bacteria streaming by the ice crystals around the wire showed the cells latching on. When the team introduced antibodies that disabled MpIBP, the bacteria slid off the ice, suggesting that the protein—which is shaped like a fishing line with a hook on the end—enables bacteria to cling to ice floes in their ocean habitat, says Braslavsky. It’s the first bacterial adhesion molecule discovered that sticks to ice.
The researchers built their device to have temperature control with millikelvin precision, crucial for studying ice because “it can just disappear” mid-experiment, says Braslavsky. Plus, the chamber’s thin design allowed for high-resolution images of individual bacteria bound to the ice.
Manipulating the adhesion protein with antibodies allowed Braslavsky’s group to disable specific structural regions one at a time, showing that only one domain in the “hook” at the very tip of MpIBP grabs onto ice. Adhesion-blocking antibodies could help prevent biofilm formation, says Braslavsky.