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Despite the importance of dimethylsulphoniopropionate (DMSP) in the global sulphur cycle and climate regulation, the biological pathways underpinning its synthesis in marine phytoplankton remain poorly understood. The intracellular concentration of DMSP increases with increased salinity, increased light intensity and nitrogen starvation in the diatom Thalassiosira pseudonana. We used these conditions to investigate DMSP synthesis at the cellular level via analysis of enzyme activity, gene expression and proteome comparison. The activity of the key sulphur assimilatory enzyme, adenosine 5'-phosphosulphate reductase was not coordinated with increasing intracellular DMSP concentration. Under all three treatments coordination in the expression of sulphur assimilation genes was limited to increases in sulphite reductase transcripts. Similarly, proteomic 2D gel analysis only revealed an increase in phosphoenolpyruvate carboxylase following increases in DMSP concentration. Our findings suggest that increased sulphur assimilation might not be required for increased DMSP synthesis, instead the availability of carbon and nitrogen substrates may be important in the regulation of this pathway. This contrasts with the regulation of sulphur metabolism in higher plants, which generally involves up-regulation of several sulphur assimilatory enzymes. In T. pseudonana changes relating to sulphur metabolism were specific to the individual treatments and, given that little coordination was seen in transcript and protein responses across the three growth conditions, different patterns of regulation might be responsible for the increase in DMSP concentration seen under each treatment.

Very short-lived halocarbons of marine biogenic origin play an important role in affecting tropospheric and stratospheric chemistry. In recent years, more attention has been paid to tropical regions where the influence of strong convective forces is responsible for rapid uplifting of the volatile organohalogens from the open surface waters into the atmosphere. This laboratory-based study reports on three common tropical marine microalgae capable of emitting a range of short-lived halocarbons, namely, CH3I, CHBr3, CH2Br2, CHBr2Cl, and CHCl3. Chlorophyll a and cell density were highly correlated to the quantity of all five compounds emitted (p < 0.01). The diatom Amphora sp. UMACC 370 had a higher range of CH3I emission rate (10.55–64.18 pmol mg−1 chl a day−1, p < 0.01) than the cyanobacterium Synechococcus sp. UMACC 371 and chlorophyte Parachlorella sp. UMACC 245 (1.04–3.86 pmol mg−1 chl a day−1 and 0–2.16 pmol mg−1 chl a day−1, p < 0.01, respectively). Furthermore, iodine was the dominant halogen emitted in terms of total combined halide mass of all three species. Overall, the emissions of short-lived halocarbons were both species- and growth phase-dependent, highlighting the importance of considering cell physiological conditions when determining gas emission rates.

It was thought that phytoplankton make DMSP, a key compound in the marine sulfur cycle, whereas bacteria use it. Now, one study shows that diatoms can also take up DMSP; another study identifies a key bacterial gene involved in its demethylation.

Volatile halocarbons can deplete the protective stratospheric ozone layer contributing to global climate change and may even affect local climate through aerosol production. These compounds are produced through anthropogenic and biogenic processes. Biogenic halocarbons may be produced as defence compounds, anti-oxidants or by-products of metabolic processes. These compounds include very short-lived halocarbons (VSLH), e.g. bromoform (CHBr3), dibromomethane (CH2Br2), methyl iodide (CH3I), diiodomethane (CH2I2). Efforts to quantify the biogenic sources of these compounds, especially those of marine origin, e.g. seaweeds, phytoplankton and seagrass meadows, are often complicated by inherent biological variability as well as spatial and temporal changes in emissions. The contribution of the coastal region and the oceans to the stratospheric load of halocarbons has been widely debated. This highlights the need to understand the factors affecting the release of these compounds from marine sources for which data for modelling purposes are generally lacking. Seaweeds are important sources of biogenic halocarbons subjected to changing environmental conditions. Huge uncertainties in the prediction of current and future global halocarbon pool exist due to the lack of spatial and temporal data input from coastal and oceanic sources. Therefore, investigating the effect of changing environmental conditions on the emission of VSLH by the seaweeds could help towards better estimations of halocarbon emissions. This is especially important in light of global changes in both climate and the environment, the expansion of seaweed cultivation industry and the interactions between halocarbon emission and their environment. In this paper, we review current knowledge of seaweed halocarbon emissions, how environmental factors affect these emissions and identify gaps in understanding. Our aim is to direct much needed research to improve understanding of the contribution of marine biogenic sources of halocarbons and their impact on the environment.

The marine iodine cycle has significant impacts on air quality and atmospheric chemistry. Specifically, the reaction of iodide with ozone in the top few micrometres of the surface ocean is an important sink for tropospheric ozone (a pollutant gas) and the dominant source of reactive iodine to the atmosphere. Sea surface iodide parameterisations are now being implemented in air quality models, but these are currently a major source of uncertainty. Relatively little observational data is available to estimate the global surface iodide concentrations, and this data has not hitherto been openly available in a collated, digital form. Here we present all available sea surface (<20 m depth) iodide observations. The dataset includes values digitised from published manuscripts, published and unpublished data supplied directly by the originators, and data obtained from repositories. It contains 1342 data points, and spans latitudes from 70°S to 68°N, representing all major basins. The data may be used to model sea surface iodide concentrations or as a reference for future observations.

The response to sulfate deficiency of plants and freshwater green algae has been extensively analysed by system biology approaches. By contrast, seawater sulfate concentration is high and very little is known about the sulfur metabolism of marine organisms. Here, we used a combination of metabolite analysis and transcriptomics to analyse the response of the marine microalga Emiliania huxleyi as it acclimated to sulfate limitation. Lowering sulfate availability in artificial seawater from 25 to 5mM resulted in significant reduction in growth and intracellular concentrations of dimethylsulfoniopropionate and glutathione. Sulfate-limited E. huxleyi cells showed increased sulfate uptake but sulfate reduction to sulfite did not seem to be regulated. Sulfate limitation in E. huxleyi affected expression of 1718 genes. The vast majority of these genes were upregulated, including genes involved in carbohydrate and lipid metabolism, and genes involved in the general stress response. The acclimation response of E. huxleyi to sulfate deficiency shows several similarities to the well-described responses of Arabidopsis and Chlamydomonas, but also has many unique features. This dataset shows that even though E. huxleyi is adapted to constitutively high sulfate concentration, it retains the ability to re-program its gene expression in response to reduced sulfate availability.

Marine algae have been reported as important sources of biogenic volatile halocarbons that are emitted into the atmosphere. These compounds are linked to destruction of the ozone layer, thus contributing to climate change. There may be mutual interactions between the halocarbon emission and the environment. In this study, the effect of irradiance on the emission of halocarbons from selected microalgae was investigated. Using controlled laboratory experiments, three tropical marine microalgae cultures, Synechococcus sp. UMACC 371 (cyanophyte), Parachlorella sp. UMACC 245 (chlorophyte) and Amphora sp. UMACC 370 (diatom) were exposed to irradiance of 0, 40 and 120 µmol photons m −2 s −1 . Stress in the microalgal cultures was indicated by the photosynthetic performance (F v /F m , maximum quantum yield). An increase in halocarbon emissions was observed at 120 µmol photons m −2 s −1 , together with a decrease in F v /F m . This was most evident in the release of CH 3 I by Amphora sp. Synechococcus sp. was observed to be the most affected by irradiance as shown by the increase in emissions of most halocarbons except for CHBr 3 and CHBr 2 Cl. High positive correlation between F v /F m and halocarbon emission rates was observed in Synechococcus sp. for CH 2 Br 2 . No clear trends in correlation could be observed for the other halocarbons in the other two microalgal species. This suggests that other mechanisms like mitochondria respiration may contribute to halocarbon production, in addition to photosynthetic performance.

Dimethyl sulfide (DMS) is a key compound in global sulfur and carbon cycles. DMS oxidation products cause cloud nucleation and may affect weather and climate. DMS is generated largely by bacterial catabolism of dimethylsulfoniopropionate (DMSP), a secondary metabolite made by marine algae. We demonstrate that the bacterial gene dddD is required for this process and that its transcription is induced by the DMSP substrate. Cloned dddD from the marine bacterium Marinomonas and from two bacterial strains that associate with higher plants, the N₂-fixing symbiont Rhizobium NGR234 and the root-colonizing Burkholderia cepacia AMMD, conferred to Escherichia coli the ability to make DMS from DMSP. The inferred enzymatic mechanism for DMS liberation involves an initial step in which DMSP is modified by addition of acyl coenzyme A, rather than the immediate release of DMS by a DMSP lyase, the previously suggested mechanism.

Prymnesium parvum is a toxin-producing haptophyte that causes harmful algal blooms globally, leading to large-scale fish kills that have severe ecological and economic implications. For the model haptophyte, Emiliania huxleyi, it has been shown that large dsDNA viruses play an important role in regulating blooms and therefore biogeochemical cycling, but much less work has been done looking at viruses that infect P. parvum, or the role that these viruses may play in regulating harmful algal blooms. In this study, we report the isolation and characterization of a lytic nucleo-cytoplasmic large DNA virus (NCLDV) collected from the site of a harmful P. parvum bloom. In subsequent experiments, this virus was shown to infect cultures of Prymnesium sp. and showed phylogenetic similarity to the extended Megaviridae family of algal viruses.

Five tropical seaweeds, Kappaphycus alvarezii (Doty) Doty ex P.C. Silva, Padina australis Hauck, Sargassum binderi Sonder ex J. Agardh (syn. S. aquifolium (Turner) C. Agardh), Sargassum siliquosum J. Agardh and Turbinaria conoides (J. Agardh) Kützing, were incubated in seawater of pH 8.0, 7.8 (ambient), 7.6, 7.4 and 7.2, to study the effects of changing seawater pH on halocarbon emissions. Eight halocarbon species known to be emitted by seaweeds were investigated: bromoform (CHBr 3 ), dibro­momethane (CH 2 Br 2 ), iodomethane (CH 3 I), diiodomethane (CH 2 I 2 ), bromoiodomethane (CH 2 BrI), bromochlorometh­ane (CH 2 BrCl), bromodichloromethane (CHBrCl 2 ), and dibro­mochloromethane (CHBr 2 Cl). These very short-lived halocarbon gases are believed to contribute to stratospheric halogen concentrations if released in the tropics. It was observed that the seaweeds emit all eight halocarbons assayed, with the exception of K. alvarezii and S. binderi for CH 2 I 2 and CH 3 I respectively, which were not measurable at the achievable limit of detection. The effect of pH on halocarbon emission by the seaweeds was shown to be species-specific and compound specific. The highest percentage changes in emissions for the halocarbons of interest were observed at the lower pH levels of 7.2 and 7.4 especially in Padina australis and Sargassum spp., showing that lower seawater pH causes elevated emissions of some halocarbon compounds. In general the seaweed least affected by pH change in terms of types of halocarbon emission, was P. australis . The commercially farmed seaweed K. alvarezii was very sensitive to pH change as shown by the high increases in most of the compounds in all pH levels relative to ambient. In terms of percentage decrease in maximum quantum yield of photosynthesis ( F v ∕ F m ) prior to and after incubation, there were no significant correlations with the various pH levels tested for all seaweeds. The correlation between percentage decrease in the maximum quantum yield of photosynthesis ( F v ∕ F m ) and halocarbon emission rates, was significant only for CH 2 BrCl emission by P. australis ( r  = 0.47; p  ≤ 0.04), implying that photosynthesis may not be closely linked to halocarbon emissions by the seaweeds studied. Bromine was the largest contributor to the total mass of halogen emitted for all the seaweeds at all pH. The highest total amount of bromine emitted by K. alvarezii (an average of 98% of total mass of halogens) and the increase in the total amount of chlorine with decreasing seawater pH fuels concern for the expanding seaweed farming activities in the ASEAN region.