Proteomic Analysis of a Sea-Ice Diatom: Salinity Acclimation Provides New Insight into the Dimethylsulfoniopropionate Production Pathway      

Abstract

Dimethylsulfoniopropionate (DMSP) plays important roles in oceanic carbon and sulfur cycling and may significantly impact climate. It is a biomolecule synthesized from the methionine (Met) pathway and proposed to serve various physiological functions to aid in environmental stress adaptation through its compatible solute, cryoprotectant, and antioxidant properties. Yet, the enzymes and mechanisms regulating DMSP production are poorly understood. This study utilized a proteomics approach to investigate protein changes associated with salinity-induced DMSP increases in the model sea-ice diatom Fragilariopsis cylindrus (CCMP 1102). We hypothesized proteins associated with the Met-DMSP biosynthesis pathway would increase in relative abundance when challenged with elevated salinity. To test this hypothesis axenic log-phase cultures initially grown at a salinity of 35 were gradually shifted to a final salinity of 70 over a 24-h period. Intracellular DMSP was measured and two-dimensional gel electrophoresis was used to identify protein changes at 48 h after the shift. Intracellular DMSP increased by approximately 85% in the hypersaline cultures. One-third of the proteins increased under high salinity were associated with amino acid pathways. Three protein isoforms of S-adenosylhomo-cysteine hydrolase, which synthesizes a Met precursor, increased 1.8-to 2.1-fold, two isoforms of S-adenosyl Met synthetase increased 1.9-to 2.5-fold, and S-adenosyl Met methyltransferase increased by 2.8-fold, suggesting active methyl cycle proteins are recruited in the synthesis of DMSP. Proteins from the four enzyme classes of the proposed algal Met transaminase DMSP pathway were among the elevated proteins, supporting our hypothesis and providing candidate genes for future characterization studies.

Snowball cooling after algal rise

“…Both lineages branched early in Earth's history 16 , but it is not clear whether early forms of these modern algae had the ability to synthesize DMSP. Although the enzymatic steps of the DMSP biosynthetic pathway are known from Ulvophyceae 19 and related candidate genes have tentatively been identified 20 , as yet there is insufficient detail to identify the phylogenetic distribution of DMSP synthesis with public sequence databases (Supplementary Information). Instead, we used literature-derived information on the presence of intracellular DMSP 18,21 to infer the capacity for its biosynthesis in various extant algae ( Fig.…”

Metatranscriptomes reveal functional variation in diatom communities from the Antarctic Peninsula

“…seawater Kroon, 2002a, 2002b), we sampled ice near the ice-water interface (surface to 5-10 cm depth), where somewhat higher nutrient levels are expected (Lyon et al, 2011). Interestingly, urea transporters were relatively enriched in WKI, suggesting that reduced organic N from heterotrophic sources may provide additional N within sea ice brine channels ( Table 2).…”

Methylcrotonyl-CoA Carboxylase Regulates Triacylglycerol Accumulation in the Model Diatom Phaeodactylum tricornutum

“…In recent years, different proteomics approaches have been undertaken to investigate various aspects of diatom biology and have provided new insights into the adaptive responses of diatoms to different environmental and growth conditions (Lyon et al, 2011;Bertrand et al, 2012;Hockin et al, 2012). With recent advances in mass spectrometry, label-free quantitative proteomic approaches have progressed and are now considered to be reliable, robust, and efficient methods to study changes in protein abundance in complex mixtures (Geetha et al, 2011;Megger et al, 2013).…”