Changes in biochemical compositions and proteomic profiles of Saccharina japonica upon the colonization by bryozoans and hydrozoans

Abstract

ABSTRACT Epiphytic colonization on Saccharina japonica has become a major challenge to the seaweed industry, and avoiding it during the cultivation period is difficult. Several epiphytic species are involved in fouling in the temperate sea; among them, the worst is caused by the encrusting bryozoans and the stoloniferous hydrozoans. These epiphytic colonizations are thought to cause negative impacts on the seaweed biochemical composition and growth. Hence, epizootic colonization may lead to changes in biochemical composition at the protein level of the host. Therefore, in this study we have investigated the effect of bryozoans and hydrozoans colonization on the biochemical composition and tissue viability of the phaeophyte S. japonica. Also possible induced changes in the proteomic profile of the seaweed upon the colonization by the two epibionts were investigated. Finally, earlier colonization marker proteins were indentified from lately bryozoans/hydrozoans colonized and the nearby S. japonica tissue. In the first study, the encrusting bryozoans on S. japonica contained high levels of crude ash (657 g Kg -1 dry weight) and arsenic (49 mg Kg-1 dry weight) exceeding the recommended range for human consumption, and had relatively low levels of essential amino acids. The content of inorganic arsenic in bryozoans was 31% of the inorganic arsenic provisional tolerable weekly intake (PTWI) established by the World Health Organization. After removing the bryozoans, we found that the seaweed blade tissues beneath the colonies had elevated levels of potassium, iodine, and docosahexaenoic acid, and reduced levels of copper, chromium, and cadmium compared to healthy tissues. Similarly, the stoloniferous hydrozoan on S. japonica contained high amount of zinc (1.7 g kg -1 dry weight), which is 23% against the PTWI, at levels higher than the recommended range in food. In seaweed blades beneath the colony, after the removal of hydrozoans, levels of selenium, iodine, and docosahexaenoic acid increased, while copper, cadmium, nickel, chromium, and erucic acid levels decreased compared to healthy tissues. Also colonized tissues after removing the bryozoans and hydrozoans showed reduced viability by 69% and 77% respectively compared to healthy tissues. In the second study, from proteomic profiles of S. japonica, 145 and 91 protein spots were detected from bryozoans-colonized and healthy tissues, respectively. Among them, 69 and 32 spots were significantly up- and down-regulated, respectively, in expression level upon bryozoans colonization. Similarly, a total of 75 and 91 protein spots were identified in the healthy and hydrozoan-colonized tissues respectively. Among them 77 and 28 spots were up- and down-regulated by significant difference of expression level upon the colonization. Upon both colonizations most of the up- and down-regulated proteins are known to be related in stress control, defense mechanism, signal transduction, photosynthesis, protein metabolism, and cytoskeleton. Based on the fact that the colonization by the epibionts changed the biochemical composition and proteomic profile of S. japonica, the objective of our third study was to identify earlier colonization marker proteins upon both bryozoans and hydrozoans. Accordingly, we identified some significantly differentially express-ed earlier colonization marker proteins from the lately-colonized and nearby tissues to the lately bryozoans-colonized S. japonica. These included, zinc finger protein, actin, kinase, thioredoxin domain containing protein 3, ATP synthesis related proteins, GTPase Activating Protein (GAP), Glutamyl tRNA Reductase (GluTR), Leucine Rich Repeat (LRR) and Nucleotide Binding (NB)-ARC doma-ins, two-component response regulator PilR, serine-pyruvate aminotransferase, 50S ribosomal protein L1P, ATP synthase beta-subunit, keratin type 1 cytoskelet-al and splicing factor arginine/serine rich. Similarly, from the nearby tissues and in the lately hydrozoan-colonized S. japonica, ATP synthase beta-subunit partial (chloroplast)/ATP synthase CF1 beta chain (chloroplast), cytochrome P450, two-component response regulator, expa-nsin, signal-induced proliferation-associated 1-like protein isoform X4, actin, pro-tein kinase, ubiquitin-transferase, adenosine deaminase, kinesin were identified as potential earlier colonization marker prote-ins. Considering the spot intensity, being identified in the nearby non-colonized tissues to the lately-colonized tissue and the lately colonized tissue itself and functioning in plant biotic/abiotc stress responses, the above mentioned proteins identified in the earlier phase of the colonization, can be potential colonization marker proteins. In conclusion, as evaluated for food or fodder, bryozoans and hydrozoans deteriorate the quality of the seaweed. Thus, both the lacy crust bryozoans and stoloniferous hydrozoans must be removed from the surface of seaweed prior to its use as food or fodder.