Partial characterisation of dimethylsulfoniopropionate (DMSP) lyase isozymes in 6 strains of Emiliania huxleyi

We characterised and compared dimethylsulfoniopropionate (DMSP) lyase isozymes in crude extracts of 6 axenic Emiliania huxleyi cultures (CCMP 370, 373, 374, 379, 1516, and strain L). This enzyme cleaves DMSP to form dimethyl sulfide (DMS), acrylate and a proton, but the function of this reaction in algae is still poorly understood. Most of the cultures produced high concentrations of intracellular DMSP, which was constant over the growth cycle and ranged from 157 to 242 mM, except for 1516 which had 50 mM DMSP cell-1. Extracts of all strains produced DMS from exogenous DMSP in vitro. DMSP lyases appeared constitutive, but enzyme activity and behaviour varied greatly among strains, and did not correlate with intracellular DMSP concentration. Strains 373 and 379 showed high DMSP lyase activities (12.5 and 6.1 fmol DMS cell-1 min-1, respectively), whereas DMS production was more than 100-fold lower in 370, 374, 1516 and L. This difference was intrinsic and the general pattern of high- and low-activity strains remained true over more than a 1 yr cultivation period. The cleavage reaction was optimal at pH 6 in the strains with high lyase activity and pH 5 was optimal for 374, 1516 and L. Strain 370 showed increasing activity with increasing pH. Experiments with additions of 0.125 to 2 M NaCl indicated halotolerant DMSP lyases in 373, 379 and 374. However, the halophilic DMSP lyases in 370 and L required 1 M NaCl addition for optimal DMSP cleavage, and 1516 showed optimal activity at 2 M NaCl. These results suggest that there are several structurally different DMSP lyase isozymes within E. huxleyi. However, it cannot be ruled out that varying concentrations of DMSP lyase per cell may have contributed to the differences in enzyme activity per cell. Comparison with other algal taxa indicates several families of DMSP lyases, hinting at possibly different cellular locations and functions, and varying DMS production under natural conditions

Short-Lived Trace Gases in the Surface Ocean and the Atmosphere

The two-way exchange of trace gases between the ocean and the atmosphere is important for both the chemistry and physics of the atmosphere and the biogeochemistry of the oceans, including the global cycling of elements. Here we review these exchanges and their importance for a range of gases whose lifetimes are generally short compared to the main greenhouse gases and which are, in most cases, more reactive than them. Gases considered include sulphur and related compounds, organohalogens, non-methane hydrocarbons, ozone, ammonia and related compounds, hydrogen and carbon monoxide. Finally, we stress the interactivity of the system, the importance of process understanding for modeling, the need for more extensive field measurements and their better seasonal coverage, the importance of inter-calibration exercises and finally the need to show the importance of air-sea exchanges for global cycling and how the field fits into the broader context of Earth System Science

Local environment shapes adaptation of Phaeocystis antarctica to salinity perturbations: Evidence for physiological resilience

The Southern Ocean (SO) is a fragile ecosystem as judged by changes in the timing of the advance and retreat of its ice cover. In the SO, the Antarctic Circumpolar Current (ACC) and the near shore gyres (Weddell Sea and Ross Sea) provide local environments with distinct temperature and salinity attributes associated with varying sea ice history. Phaeocystis antarctica is a prymnesiophyte often dominating polar phytoplankton blooms in the (SO) and is a keystone species there because its abundance can have negative effects on higher trophic levels and it can influence air/sea gas exchange involved in DMSP production, Thus, its ability to survive in response to perturbations in the environments may be linked to its genetic diversity within its populations as they move around the SO. Here we apply increased (70 PSU) and decreased (18 PSU) salinity treatments to five genetically different P. antarctica strains isolated from three different water masses to test whether genetic similarity or water mass physical features were more important in determining responses to salinity changes, such as those encountered by inclusion into sea ice brine channels and/or its subsequent melt water in those water masses that have annual ice cover. Strains that were geographically close (isolated from the same water mass), but genetically distinct (ca. 30% similar and from different gene pools as judged by microsatellite (MS) and amplified fragment linked polymorphisms (AFLP) analyses responded similarly to higher and lower salinity regimes, whereas genetically close strains (ca. 95% identical or from the same gene pool) that originated from different water masses and hence different environmental conditions responded differently. Dimethylsulphoniopropionate (DMSP) production in response to these salinity changes were not significantly different between any of the strains/treatments. Considering the presence of highly similar genotypes in ice-free as well as seasonally ice covered sampling sites, the observed phenotypic differences most likely result from rapid local adaptation between both habitat types or a hybridization of isolates from the two gene pools with the resultant genotype for salinity tolerance being that from which the isolate originated, suggesting that the selective effect of seasonal presence or year-round absence of sea ice overrides gene flow between these habitats to adapt the physiology of cells to the environment in a relatively short period of time