Exploring respiration and respiratory electron transport system (ETS) in Ulva spp.

[ES] Respiration is a key ecological index. For either individuals or communities, it can be use to assess carbon and energy, demand and expenditure as well as carbon flow rates through food webs. When combined with productivity measurements it can establish the level of metabolic balance. When combined with measurements of respiratory capacity, it can indicate physiological state. Here, we report pilot studies the metabolism of the green algae, Ulva rotundata that inhabits intertidal pools of Gran Canaria. As a starting point we used the electron transport system (ETS) to differentiate between different growing conditions in the natural environment. We suspected different levels of stress associated with these conditions and looked for the influence of this stress in the ETS measurements. This technique has been successfully applied to study bacteria, phytoplankton and zooplankton in the ocean, but it has not been used to study sessile marine macroalgae. These neritic and littoral macrophytes have major ecological and industrial importance, yet little is known about their respiratory physiology. Such knowledge would strengthen our understanding of the resources of the coastal ocean and facilitate its development and best use. Here, we modified the ETS methodology for Ulva rotundata. With this modified ETS assay we investigated the capacity of Ulva to resist anoxia. We measured respiration with optodes (Fibox 4, Presens) in the dark to the point of oxygen exhaustion and through 24 h of anoxia. Then we exposed the Ulva to light and followed the oxygen increase due to photosynthesis. We discuss here the capacity of Ulva to survive during anoxia.

Carbon flux, nutrient retention efficiency and the curvature of respiration depth-profiles in the ocean water column

Trabajo realizado por: Packard, T. T., Osma, N., Fernández Urruzola, I., Gómez, M

Respiration in the dark ocean

[EN]The dark ocean, the waters below 200 m depth, comprises about 95% of the volume of the ocean, but its contribution to the metabolism of the ocean is poorly quantified. Here we show that the respiration rate of microplankton declines exponentially at a rate of 0.53 km−1 in the dark ocean, and is enhanced at the interface between the mesopelagic and the abyssal layers (1,000–2,000 m). The respiratory CO2 production in the dark ocean, estimated at 20 to 33.3 Gt C yr−1, renders it a major component of the carbon flux in the biosphere.

Active mesopelagic prokaryotes support high respiration in the subtropical northeast Atlantic Ocean

[EN]Here we provide evidence, based on prokaryote metabolic proxies and direct estimates of oxygen consumption, that the mesopelagic prokaryote assemblage in the subtropical Northeast Atlantic is an active one. It supports a high respiration (0.22 ± 0.05 μmol O2 l−1 d−1, corresponding to 68 ± 8 mmol CO2 m−2 d−1), comparable to that of the epipelagic zone during the same period (64–97 mmol C m−2 d−1). Our findings suggest that mesopelagic prokaryotes in the NE subtropical Ocean, as well as in other eastern boundary regions, are important carbon sinks for organic matter advected from the highly productive coastal systems, and would play a key role in the global carbon cycle of the oceans.

The photosynthetic bacterial reaction center in native and artificial envirnoments: effects on light-induced electron transfer

In this thesis we focussed on the characterization of the reaction center (RC) protein purified from the photosynthetic bacterium Rhodobacter sphaeroides. In particular, we discussed the effects of native and artificial environment on the light-induced electron transfer processes. The native environment consist of the inner antenna LH1 complex that copurifies with the RC forming the so called core complex, and the lipid phase tightly associated with it. In parallel, we analyzed the role of saccharidic glassy matrices on the interplay between electron transfer processes and internal protein dynamics. As a different artificial matrix, we incorporated the RC protein in a layer-by-layer structure with a twofold aim: to check the behaviour of the protein in such an unusual environment and to test the response of the system to herbicides. By examining the RC in its native environment, we found that the light-induced charge separated state P+QB - is markedly stabilized (by about 40 meV) in the core complex as compared to the RC-only system over a physiological pH range. We also verified that, as compared to the average composition of the membrane, the core complex copurifies with a tightly bound lipid complement of about 90 phospholipid molecules per RC, which is strongly enriched in cardiolipin. In parallel, a large ubiquinone pool was found in association with the core complex, giving rise to a quinone concentration about ten times larger than the average one in the membrane. Moreover, this quinone pool is fully functional, i.e. it is promptly available at the QB site during multiple turnover excitation of the RC. The latter two observations suggest important heterogeneities and anisotropies in the native membranes which can in principle account for the stabilization of the charge separated state in the core complex. The thermodynamic and kinetic parameters obtained in the RC-LH1 complex are very close to those measured in intact membranes, indicating that the electron transfer properties of the RC in vivo are essentially determined by its local environment. The studies performed by incorporating the RC into saccharidic matrices evidenced the relevance of solvent-protein interactions and dynamical coupling in determining the kinetics of electron transfer processes. The usual approach when studying the interplay between internal motions and protein function consists in freezing the degrees of freedom of the protein at cryogenic temperature. We proved that the “trehalose approach” offers distinct advantages with respect to this traditional methodology. We showed, in fact, that the RC conformational dynamics, coupled to specific electron transfer processes, can be modulated by varying the hydration level of the trehalose matrix at room temperature, thus allowing to disentangle solvent from temperature effects. The comparison between different saccharidic matrices has revealed that the structural and dynamical protein-matrix coupling depends strongly upon the sugar. The analyses performed in RCs embedded in polyelectrolyte multilayers (PEM) structures have shown that the electron transfer from QA - to QB, a conformationally gated process extremely sensitive to the RC environment, can be strongly modulated by the hydration level of the matrix, confirming analogous results obtained for this electron transfer reaction in sugar matrices. We found that PEM-RCs are a very stable system, particularly suitable to study the thermodynamics and kinetics of herbicide binding to the QB site. These features make PEM-RC structures quite promising in the development of herbicide biosensors. The studies discussed in the present thesis have shown that, although the effects on electron transfer induced by the native and artificial environments tested are markedly different, they can be described on the basis of a common kinetic model which takes into account the static conformational heterogeneity of the RC and the interconversion between conformational substates. Interestingly, the same distribution of rate constants (i.e. a Gamma distribution function) can describe charge recombination processes in solutions of purified RC, in RC-LH1 complexes, in wet and dry RC-PEM structures and in glassy saccharidic matrices over a wide range of hydration levels. In conclusion, the results obtained for RCs in different physico-chemical environments emphasize the relevance of the structure/dynamics solvent/protein coupling in determining the energetics and the kinetics of electron transfer processes in a membrane protein complex.