Sulphur compounds, methane, and phytoplankton during SONNE cruise SO202/2 (Transbrom Sonne)

Here we present results of the first comprehensive study of sulphur compounds and methane in the oligotrophic tropical West Pacific Ocean. The concentrations of dimethylsuphide (DMS), dimethylsulphoniopropionate (DMSP), dimethylsulphoxide (DMSO), and methane (CH4), as well as various phytoplankton marker pigments in the surface ocean were measured along a north-south transit from Japan to Australia in October 2009. DMS (0.9 nmol/l), dissolved DMSP (DMSPd, 1.6 nmol/l) and particulate DMSP (DMSPp, 2 nmol/l) concentrations were generally low, while dissolved DMSO (DMSOd, 4.4 nmol/l) and particulate DMSO (DMSOp, 11.5 nmol/l) concentrations were comparably enhanced. Positive correlations were found between DMSO and DMSP as well as DMSP and DMSO with chlorophyll a, which suggests a similar source for both compounds. Similar phytoplankton groups were identified as being important for the DMSO and DMSP pool, thus, the same algae taxa might produce both DMSP and DMSO. In contrast, phytoplankton seemed to play only a minor role for the DMS distribution in the western Pacific Ocean. The observed DMSPp : DMSOp ratios were very low and seem to be characteristic of oligotrophic tropical waters representing the extreme endpoint of the global DMSPp : DMSOp ratio vs. SST relationship. It is most likely that nutrient limitation and oxidative stress in the tropical West Pacific Ocean triggered enhanced DMSO production leading to an accumulation of DMSO in the sea surface. Positive correlations between DMSPd and CH4, as well as between DMSO (particulate and total) and CH4, were found along the transit. We conclude that both DMSP and DMSO serve as substrates for methanogenic bacteria in the western Pacific Ocean.

Methane measurements during POLARSTERN cruise ARK-XXII/2

A methane surplus relative to the atmospheric equilibrium is a frequently observed feature of ocean surface water. Despite the common fact that biological processes are responsible for its origin, the formation of methane in aerobic surface water is still poorly understood. We report on methane production in the central Arctic Ocean, which was exclusively detected in Pacific derived water but not nearby in Atlantic derived water. The two water masses are distinguished by their different nitrate to phosphate ratios. We show that methane production occurs if nitrate is depleted but phosphate is available as a P source. Apparently the low N:P ratio enhances the ability of bacteria to compete for phosphate while the phytoplankton metabolite dimethylsulfoniopropionate (DMSP) is utilized as a C source. This was verified by experimentally induced methane production in DMSP spiked Arctic sea water. Accordingly we propose that methylated compounds may serve as precursors for methane and thermodynamic calculations show that methylotrophic methanogenesis can provide energy in aerobic environments.

Defence chemistry modulation by light and temperature (results in 4 excel files, zipped)

The goals of this study were (1) to investigate whether Fucus vesiculosus regulates the production of its antifouling defence chemicals against microfoulers in response to light limitation and temperature shifts and (2) to investigate if different surface concentrations of defence compounds shape epibacterial communities. F. vesiculosus was incubated in indoor mesocosms at five different temperature conditions (5 to 25°C) and in outdoor mesocosms under six differently reduced sunlight conditions (0 to 100%), respectively. Algal surface concentrations of previously identified antifouling compounds - dimethylsulphopropionate (DMSP), fucoxanthin and proline - were determined and the bacterial community composition was characterized by in-depth sequencing of the 16S-rRNA gene. Altogether, the effect of different treatment levels upon defence compound concentrations was limited. Under all conditions DMSP alone appeared to be sufficiently concentrated to warrant for at least a partial inhibitory action against epibiotic bacteria of F. vesiculosus. In contrast, proline and fucoxanthin rarely reached the necessary concentration ranges for self-contained inhibition. Nonetheless, in both experiments along with the direct influence of temperature and light, all three compounds apparently affected (and thereby shaped) the overall bacterial community composition associated with F. vesiculosus since tendencies for insensitivity towards all three compounds were observed among bacterial taxa that typically dominate those communities. Given that the concentrations of at least one of the compounds (in most cases DMSP) were always high enough to inhibit bacterial settlement, we conclude that the capacity of F. vesiculosus for such defence will hardly be compromised by shading or warming to temperatures up to 25°C.

Dimethylsulfoniopropionate Biosynthesis in Spartina alterniflora1 : Evidence That S-Methylmethionine and Dimethylsulfoniopropylamine Are Intermediates

The osmoprotectant 3-dimethylsulfoniopropionate (DMSP) occurs in Gramineae and Compositae, but its synthesis has been studied only in the latter. The DMSP synthesis pathway was therefore investigated in the salt marsh grass Spartina alterniflora Loisel. Leaf tissue metabolized supplied [35S]methionine (Met) to S-methyl-l-Met (SMM), 3-dimethylsulfoniopropylamine (DMSP-amine), and DMSP. The 35S-labeling kinetics of SMM and DMSP-amine indicated that they were intermediates and, consistent with this, the dimethylsulfonium moiety of SMM was shown by stable isotope labeling to be incorporated as a unit into DMSP. The identity of DMSP-amine, a novel natural product, was confirmed by both chemical and mass-spectral methods. S. alterniflora readily converted supplied [35S]SMM to DMSP-amine and DMSP, and also readily converted supplied [35S]DMSP-amine to DMSP; grasses that lack DMSP did neither. A small amount of label was detected in 3-dimethylsulfoniopropionaldehyde (DMSP-ald) when [35S]SMM or [35S]DMSP-amine was given. These results are consistent with the operation of the pathway Met → SMM → DMSP-amine → DMSP-ald → DMSP, which differs from that found in Compositae by the presence of a free DMSP-amine intermediate. This dissimilarity suggests that DMSP synthesis evolved independently in Gramineae and Compositae.

Salinity Promotes Accumulation of 3-Dimethylsulfoniopropionate and Its Precursor S-Methylmethionine in Chloroplasts1

Wollastonia biflora (L.) DC. plants accumulate the osmoprotectant 3-dimethylsulfoniopropionate (DMSP), particularly when salinized. DMSP is known to be synthesized in the chloroplast from S-methylmethionine (SMM) imported from the cytosol, but the sizes of the chloroplastic and extrachloroplastic pools of these compounds are unknown. We therefore determined DMSP and SMM in mesophyll protoplasts and chloroplasts. Salinization with 30% (v/v) artificial seawater increased protoplast DMSP levels from 4.6 to 6.0 μmol mg−1 chlorophyll (Chl), and chloroplast levels from 0.9 to 1.9 μmol mg−1 Chl. The latter are minimum values because intact chloroplasts leaked DMSP during isolation. Correcting for this leakage, it was estimated that in vivo about one-half of the DMSP is chloroplastic and that stromal DMSP concentrations in control and salinized plants are about 60 and 130 mm, respectively. Such concentrations would contribute significantly to chloroplast osmoregulation and could protect photosynthetic processes from stress injury. SMM levels were measured using a novel mass-spectrometric method. About 40% of the SMM was located in the chloroplast in unsalinized W. biflora plants, as was about 80% in salinized plants; the chloroplastic pool in both cases was approximately 0.1 μmol mg−1 Chl. In contrast, ≥85% of the SMM was extrachloroplastic in pea (Pisum sativum L.) and spinach (Spinacia oleracea L.), which lack DMSP. DMSP synthesis may be associated with enhanced accumulation of SMM in the chloroplast.

Identification and Stereospecificity of the First Three Enzymes of 3-Dimethylsulfoniopropionate Biosynthesis in a Chlorophyte Alga1

Many marine algae produce 3-dimethylsulfoniopropionate (DMSP), a potent osmoprotective compound whose degradation product dimethylsulfide plays a central role in the biogeochemical S cycle. Algae are known to synthesize DMSP via the four-step pathway, l-Met → 4-methylthio-2-oxobutyrate → 4-methylthio-2-hydroxybutyrate → 4-dimethylsulfonio-2-hydroxy-butyrate (DMSHB) → DMSP. Substrate-specific enzymes catalyzing the first three steps in this pathway were detected and partially characterized in cell-free extracts of the chlorophyte alga Enteromorpha intestinalis. The first is a 2-oxoglutarate-dependent aminotransferase, the second an NADPH-linked reductase, and the third an S-adenosylmethionine-dependent methyltransferase. Sensitive radiometric assays were developed for these enzymes, and used to show that their activities are high enough to account for the estimated in vivo flux from Met to DMSP. The activities of these enzymes in other DMSP-rich chlorophyte algae were at least as high as those in E. intestinalis, but were ≥20-fold lower in algae without DMSP. The reductase and methyltransferase were specific for the d-enantiomer of 4-methylthio-2-hydroxybutyrate in vitro, and both the methyltransferase step and the step(s) converting DMSHB to DMSP were shown to prefer d-enantiomers in vivo. The intermediate DMSHB was shown to act as an osmoprotectant, which indicates that the first three steps of the DMSP synthesis pathway may be sufficient to confer osmotolerance.

A Developmental Approach to Sport Expertise

This chapter examines the personal and contextual factors of youth sport that affect sport expertise and developmental outcomes. The developmental model of sport participation (DMSP) is used as a comprehensive framework that outlines different pathways of involvement in sport. Activities and contexts that promote continued sport participation and expert performance are discussed as the building blocks of all effective youth sport programs. This chapter provides evidence that performance in sport, participation, and psychological development should be considered as a whole instead of as separate entities by youth sport programmers. Adults in youth sports (i.e. coaches, parents, sport psychologists, administrators) must consider the differing implications of concepts such as deliberate play, deliberate practice, sampling, specialization, and program structure at different stages of an athlete's talent development. Seven postulates are presented regarding important transitions in youth sport and the role that sampling and deliberate play, as opposed to specialization and deliberate practice, can have during the childhood in promoting continued participation and elite performance in sport