Production of DMS from dissolved DMSP in axenic cultures of the marine phytoplankton species Phaeocystis sp.

In the marine environment, production of dimethylsulfide (DMS) from dissolved dimethylsulfoniopropionate (DMSP(d)) - an algal osmolyte - is thought to occur mainly through bacterial activity. We have investigated the possibility that phytoplankton cells convert DMSP(d) into DMS, using axenic batch cultures of Phaeocystis sp. at different growth stages. DMSP(d) added to the medium was converted enzymatically to DMS by Phaeocystis sp, A culture in the exponential growth phase displayed Michaelis-Menten type kinetics for DMSP(d) conversion, yielding an apparent K(m) value for DMSP(d) Of 11.7 +/- 3.1 muM and a V(max) value of 3.05 +/- 0.48 nmol DMS produced min-1 (10(6) cells)-1. DMSP(d) conversion rates declined during the transition from exponential to stationary growth phase, at least partly due to a diminished overall affinity of the enzyme system(s) involved in DMSP conversion. No evidence was obtained for accumulation of inhibiting substances in the medium. Intracellular DMSP concentrations in Phaeocystis sp. batch cultures increased from 71 mM in exponential-phase cells to ca 150 mM in stationary-phase cells. DMS and DMSP(d) concentrations in the culture remained very low during the exponential growth phase. DMS production started in early stationary phase. In a senescent culture DMSP(d) appeared when cell numbers started to decline. DMSP production in this culture continued even when cell numbers declined. In completely lysed batch cultures some 25% of total DMSP remained as DMSP(d). The results indicate that Phaeocystis sp. may contribute significantly to DMS production from DMSP(d) during bloom situations in the field

The carbohydrates of Phaeocystis and their degradation in the microbial food web

The ubiquity and high productivity associated with blooms of colonial Phaeocystis makes it an important contributor to the global carbon cycle. During blooms organic matter that is rich in carbohydrates is produced. We distinguish five different pools of carbohydrates produced by Phaeocystis. Like all plants and algal cells, both solitary and colonial cells produce (1) structural carbohydrates, (hetero) polysaccharides that are mainly part of the cell wall, (2) mono- and oligosaccharides, which are present as intermediates in the synthesis and catabolism of cell components, and (3) intracellular storage glucan. Colonial cells of Phaeocystis excrete (4) mucopolysaccharides, heteropolysaccharides that are the main constituent of the mucous colony matrix and (5) dissolved organic matter (DOM) rich in carbohydrates, which is mainly excreted by colonial cells. In this review the characteristics of these pools are discussed and quantitative data are summarized. During the exponential growth phase, the ratio of carbohydrate-carbon (C) to particulate organic carbon (POC) is approximately 0.1. When nutrients are limited, Phaeocystis blooms reach a stationary growth phase, during which excess energy is stored as carbohydrates. This so-called overflow metabolism increases the ratio of carbohydrate-C to POC to 0.4–0.6 during the stationary phase, leading to an increase in the C/N and C/P ratios of Phaeocystis organic matter. Overflow metabolism can be channeled towards both glucan and mucopolysaccharides. Summarizing the available data reveals that during the stationary phase of a bloom glucan contributes 0–51% to POC, whereas mucopolysaccharides contribute 5–60%. At the end of a bloom, lysis of Phaeocystis cells and deterioration of colonies leads to a massive release of DOM rich in glucan and mucopolysaccharides. Laboratory studies have revealed that this organic matter is potentially readily degradable by heterotrophic bacteria. However, observations in the field of accumulation of DOM and foam indicate that microbial degradation is hampered. The high C/N and C/P ratios of Phaeocystis organic matter may lead to nutrient limitation of microbial degradation, thereby prolonging degradation times. Over time polysaccharides tend to self-assemble into hydrogels. This may have a profound effect on carbon cycling, since hydrogels provide a vehicle to move DOM up the size spectrum to sizes subject to sedimentation. In addition, it changes the physical nature and microscale structure of the organic matter encountered by bacteria which may affect the degradation potential of the Phaeocystis organic matter.

Exposition d'étains suisses de types anciens: mai-juin 1919 : Musée des arts décoratifs de Genève

The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6-9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator-prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional great fisheries food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean. Despite this plethora of information regarding the physiological ecology of Phaeocystis, fundamental interactions between life history traits and system ecology are poorly understood. Research summarized here, and described in the various papers in this special issue, derives from a central question: how do physical (light, temperature, particle distributions, hydrodynamics), chemical (nutrient resources, infochemistry, allelopathy), biological (grazers, viruses, bacteria, other phytoplankton), and self-organizational mechanisms (stability, indirect effects) interact with life-cycle transformations of Phaeocystis to mediate ecosystem patterns of trophic structure, biodiversity, and biogeochemical fluxes? Ultimately the goal is to understand and thus predict why Phaeocystis occurs when and where it does, and the bio-feedbacks between this keystone species and the multitrophic level ecosystem. © 2007 Springer Science+Business Media B.V.SCOPUS: ch.binfo:eu-repo/semantics/publishe

Management of hyperglycaemia of type 2 diabetes. Paradigm change according to the ADA-EASD consensus report 2018

peer reviewedThe strategy for the management of hyperglycaemia in type 2 diabetes was updated in October 2018 by a group of experts of the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). They are triggered by the results of cardiovascular outcome trials published since 2015, which demonstrated a cardiovascular (and renal) protection with two classes of medications, SGLT2 inhibitors (gliflozins) and some GLP-1 receptor agonists (mainly liraglutide) in patients with established cardiovascular disease. Thus, after failure of lifestyle and metformin, the addition of one of these agents is recommended in presence of atherosclerotic cardiovascular disease. In case of heart failure or renal disease, the preference is given to a SGLT2 inhibitor, provided that estimated glomerular filtration rate is adequate (superior to 45-60 ml/min/1.73 m(2)). In all other patients, the choice is guided by the main objective, in concertation with the patient : to reduce the risk of hypoglycaemia (gliptin, gliflozin, pioglitazone or GLP1 receptor agonist), body weight excess (SGLT2 inhibitor or GLP-1 receptor) or medication cost (sulphonylurea, pioglitazone). If oral treatment is insufficient, the preference is now given to a GLP-1 receptor agonist rather than basal insulin. Thus, instead of a glucocentric and metabolic viewpoint predominant in the previous position statement, a paradigm change is proposed, focusing on cardiovascular and renal protection, within a patient-centred approach