Figure 1.
Ice-binding activities of Pyramimonas gelidicola AnM0046 and Phaeocystis antarctica CCMP1374.
A, B, Distortion of growing ice by cell-free culture media of P. gelidicola and P. antarctica, respectively. Ice c-axis is normal to page. Scale bars, 1 mm. C, Growth of ice in seawater (control). Bar, 1 mm. D. Effect of P. antarctica IBP on the structure of sea ice. L1 seawater medium (left) and L1 medium containing a natural concentration of P. antarctica IBP (right) frozen at -4.0oC. The amount of ice in the two tubes is the same. Distortion of growing ice by the IBP greatly reduces the size of brine pockets. Bar, 1 cm.
Figure 2.
Incongruence between phylogenies of polar algae based on 18S rRNA and ice-binding protein sequences trees.
Dark green symbols, Pennate diatoms; light green symbols, centric and quasi-centric diatoms; red symbols, prymnesiophyte and prasinophyte algae. IBP tree rooted with a bacterial IBP. Bootstrap values <50 are not shown. Accession numbers for the 18S sequences are Amphora sp., JQ240485; Navicula glaciei, EF106788; Fragilariopsis cylindrus, AY485467; Fragilariopsis curta, EF140623; Nitzschia stellata, JQ240484; Attheya sp., JQ240486; Chaetoceros neogracile, EU090012; Phaeocystis antarctica, X77477; Pyramimonas gelidicola, EU141942, Porphyra sp. P523, GU319853. Accession numbers of IBPs not given in the figure are given in Table S2.
Figure 3.
Neighbor-joining tree based on amino acid sequences showing best matches of algal (green symbols) and fungal (black symbols) IBPs.
None of the matches except the IBP of the bacterium Colwellia SLW05 have been confirmed to be bona fide IBPs. The tree includes all genes in GenBank that match any of the algal IBPs to within an expect value of 1xe-25. Other than self matching sequences, all nearest matches are of bacterial (unmarked) and archaeal (red symbols) proteins. Numbers at nodes indicate bootstrap values obtained with 500 resamplings. Bootstrap values <50 are not shown. Stephos is a copepod whose IBP appears to have been acquired from Chaetoceros. Accession nos. of IBPs are shown in Table S2.
Figure 4.
Bacteria in the diatom layer of sea ice.
(A) Basal plane of an ice single crystal grown in the presence of culture medium of F. frigoris. An ice-binding protein in the culture medium binds to the pit faces, allowing growth in the c-axis direction (normal to basal plane). Scale bar, 1 mm. (B) Epiphytic bacteria on a chain of the sea ice diatom Amphiprora sp. (not the Amphora of this study). Reproduced from Sullivan et al. [46] with permission. Scale bar, 2 µm.