Figure 3.

The abundance and diversity of CBA1, B₁₂ starvation indicator, and the abundance of ThiC, MetH, and MetE transcripts attributable to diatoms in Antarctic transcriptomic datasets, compared to the expression of transcripts encoding other well-characterized proteins (modified from Bertrand et al., 2012). (A) Phylogenetic tree containing CBA1 sequences from 454 metatranscriptomic (cDNA) libraries from the Ross Sea of the Southern Ocean, Monterey Bay, Puget Sound, and the North Pacific. Reference sequences from Phaeodactylum tricornutum, Fragilariopsis cylindrus, Thalassiosira pseudonana, Aureococcus anophagefferenas, and Ectocarpus siliculosus genomes were used to construct these trees and are shown in black. CBA1-like sequences from environmental samples are shown in color, as described in the key. CBA1 transcripts were detectable in diverse marine environments, suggesting that cobalamin acquisition is an important component of diatom molecular physiology. (B) The normalized abundance of Open Reading Frames (ORFs) assigned to CBA1 from within the Ross Sea is shown in blue, MetE: PF01717 is shown in green, MetH:PF02965 is shown in purple, ThiC:PF01964 in yellow, while the abundance of read counts assigned to diatom ORFs containing well-characterized pfam domains for comparison [Actin: PF00022, Histone:PF00125, GAP-DH: PF02800, Alkaline Phosphatase: PF00245, Flavodoxin: PF00258, Cytochrome b559 (PSII): PF00283, Ribose 5-phosphate isomerase A: PF06026] are shown in gray. Read counts for each ORF where summed across six libraries from Ross Sea samples and RPKM values were calculated. RPKMs were then summed across all diatom ORFs that contained that a domain of interest. CBA1, MetE, MetH, and ThiC are not among the extremely abundant transcripts (e.g., those encoding Actin, GAP-DH, Histone) but are comparable to those encoding Calvin Cycle protein Ribose 5-phosphate isomerase A, and are more abundant than the transcripts encoding a cytochrome required for photosystem II activity (b559) as well as alkaline phosphatase (AP), suggesting that they are of importance to the molecular physiology of natural diatom communities.