An ice-binding protein from an Antarctic sea ice bacterium

Abstract

An Antarctic sea ice bacterium of the Gram-negative genus Colwellia, strain SLW05, produces an extracellular substance that changes the morphology of growing ice. The active substance was identified as a $25-kDa protein that was purified through its affinity for ice. The full gene sequence was determined and was found to encode a 253-amino acid protein with a calculated molecular mass of 26 350 Da. The predicted amino acid sequence is similar to predicted sequences of ice-binding proteins recently found in two species of sea ice diatoms and a species of snow mold. A recombinant ice-binding protein showed ice-binding activity and ice recrystallization inhibition activity. The protein is much smaller than bacterial ice-nucleating proteins and antifreeze proteins that have been previously described. The function of the protein is unknown but it may act as an ice recrystallization inhibitor to protect membranes in the frozen state.

A new class of ice-binding proteins discovered in a salt-stress-induced cDNA library of the psychrophilic diatomFragilariopsis cylindrus(Bacillariophyceae)

“…Whereas proteins isolated from animals typically have the ability to depress the freezing point to actually avoid the formation of ice crystals, those proteins from plants and bacteria mainly inhibit ice re-crystallization, i.e. the growth of large ice crystals at the expense of smaller ones with smaller ones having less damaging effects on biological tissues (Griffith et al, 2005;Raymond et al, 2007). Four TUs from our library were similar to sequences encoding antifreeze proteins isolated from the snow mould fungi Typhula ishikariensis (Fig.…”

Interaction of ice binding proteins with ice, water and ions

“…[17][18][19] Inhibition of ice recrystallization is monitored by polarized optical microscopy. 6,20 The IBPs can be separated from proteins and other (serum) constituents that do not bind ice by ice-affinity purification. [21][22][23] Most important for freeze-avoiding species like fish is the ability of IBPs to prevent further growth of endogenous ice crystals circulating in the blood stream or hemolymph [ Fig.…”

Selective incorporation of dissolved organic matter (DOM) during sea ice formation

“…Such gravity drainage of brine may preferentially remove most small molecules, such as inorganic ions, which diffuse at faster rates than DOM molecules with larger size and lower diffusion rates (Granskog et al, 2004;Vancoppenolle et al, 2010;Maus et al, 2011). Another explanation suggests that bacterial and algal extracellular polymeric substances (EPSs) form gel-like structures that selectively retain DOM in sea ice (Raymond et al, 2007;Underwood et al, 2010;Krembs et al, 2011). Therefore, experimental evidence is needed to resolve the process of the enrichment of DOM during ice formation, especially considering the enormous volume of sea ice that forms, consolidates and subsequently melts in polar and sub-polar oceans and seas.…”