Growth suppression of ice crystal basal face in the presence of a moderate ice-binding protein does not confer hyperactivity

Abstract

Ice-binding proteins (IBPs) affect ice crystal growth by attaching to crystal faces. We present the effects on the growth of an ice single crystal caused by an ice-binding protein from the sea ice microalga (IBP) that is characterized by the widespread domain of unknown function 3494 (DUF3494) and known to cause a moderate freezing point depression (below 1 °C). By the application of interferometry, bright-field microscopy, and fluorescence microscopy, we observed that the IBP attaches to the basal faces of ice crystals, thereby inhibiting their growth in the direction and resulting in an increase in the effective supercooling with increasing IBP concentration. In addition, we observed that theIBP attaches to prism faces and inhibits their growth. In the event that the effective supercooling is small and crystals are faceted, this process causes an emergence of prism faces and suppresses crystal growth in the direction. When the effective supercooling is large and ice crystals have developed into a dendritic shape, the suppression of prism face growth results in thinner dendrite branches, and growth in the direction is accelerated due to enhanced latent heat dissipation. Our observations clearly indicate that the IBP occupies a separate position in the classification of IBPs due to the fact that it suppresses the growth of basal faces, despite its moderate freezing point depression.

Ice‐binding proteins and the ‘domain of unknown function’ 3494 family

“…Indeed, FIPA analysis of Tis IBP6 and Euplotes focardii bacterial consortium IBP ( Efc IBP) showed that these moderate IBPs are able to bind basal and other planes . This binding pattern to ice crystal planes was confirmed also for the moderate IBP isoform 11 from the sea‐ice diatom Fragilariopsis cylindrus ( fc IBP11) by laser confocal fluorescence microscopy of a single ice crystal in a solution of the fluorescently labelled protein . In addition to these experimental methods, MD simulations of fc IBP11 indicated that the protein can, at least partly, bind the primary prism and basal faces, despite its moderate activity .…”

“…By attaching to the icy walls of the channels the IBPs may make them more convoluted, therefore decelerating brine drainage from the sea‐ice layer and increasing the habitable space (Fig. A) . Indeed, several species of fungi, bacteria and diatoms have been confirmed to secrete their DUF3494 IBPs into the growth media, from where they could work to carve out a niche for their host organisms in the ice .…”

“…To help visualize the IBPs’ binding planes, a fluorescence‐based ice plane affinity (FIPA) analysis was developed , whereas other studies applied laser confocal fluorescence microscopy . FIPA analysis, based on the traditional ice etching method requires the use of fluorescently labelled IBPs, which are incorporated into a macroscopic single ice crystal hemisphere during its slow growth .…”

“…For instance, the Antarctic bacterium Marinomonas primoryensis uses a multidomain protein with ice‐binding activity to adhere to both diatoms and surface sea‐ice, hence forming an oxygen/nutrient‐rich zone in their environment . Lastly, many different microorganisms isolated from snow, sea‐ice and polar terrestrial and marine environments secrete IBPs that, in addition to a freeze tolerance function, potentially increase their habitable space by altering the morphology of surrounding ice .…”

Systematic and functional analysis of horizontal gene transfer events in diatoms

“…interfere with the growth of ice 50 . Ice-binding proteins were found to be laterally transferred from a 136 basidiomycete lineage to Fragilariopsis curta and F. cylindrus 51 .…”