Abstract:Little is known on the antioxidant activity modulation in microalgae, even less in diatoms. Antioxidant molecule concentrations and their modulation in microalgae has received little attention and the interconnection between light, photosynthesis, photoprotection, and antioxidant network in microalgae is still unclear. To fill this gap, we selected light as external forcing to drive physiological regulation and acclimation in the costal diatom Skeletonema marinoi. We investigated the role of light regime on th… Show more
“…Although the xanthophyll cycle pigment content is informative of light (and/or other growth conditions) acclimation, it is not necessarily a proxy for nonphotochemical quenching‐related capacity because de‐epoxidized xanthophylls Dt, Z and A can play other photoprotective roles than triggering NPQ (see for instance Havaux and García‐Plazaola , Smerilli et al. ). Xanthophyll cycle‐mediated NPQ is also determined by the QE of the de‐epoxidized xanthophylls.…”
Xanthophyll cycle‐related nonphotochemical quenching (NPQ), which is present in most photoautotrophs, allows dissipation of excess light energy. Xanthophyll cycle‐related NPQ depends principally on xanthophyll cycle pigments composition and their effective involvement in NPQ. Xanthophyll cycle‐related NPQ is tightly controlled by environmental conditions in a species‐/strain‐specific manner. These features are especially relevant in microalgae living in a complex and highly variable environment. The goal of this study was to perform a comparative assessment of NPQ ecophysiologies across microalgal taxa in order to underline the specific involvement of NPQ in growth adaptations and strategies. We used both published results and data acquired in our laboratory to understand the relationships between growth conditions (irradiance, temperature, and nutrient availability), xanthophyll cycle composition, and xanthophyll cycle pigments quenching efficiency in microalgae from various taxa. We found that in diadinoxanthin‐containing species, the xanthophyll cycle pigment pool is controlled by energy pressure in all species. At any given energy pressure, however, the diatoxanthin content is higher in diatoms than in other diadinoxanthin‐containing species. XC pigments quenching efficiency is species‐specific and decreases with acclimation to higher irradiances. We found a clear link between the natural light environment of species/ecotypes and quenching efficiency amplitude. The presence of diatoxanthin or zeaxanthin at steady state in all species examined at moderate and high irradiances suggests that cells maintain a light‐harvesting capacity in excess to cope with potential decrease in light intensity.
“…Although the xanthophyll cycle pigment content is informative of light (and/or other growth conditions) acclimation, it is not necessarily a proxy for nonphotochemical quenching‐related capacity because de‐epoxidized xanthophylls Dt, Z and A can play other photoprotective roles than triggering NPQ (see for instance Havaux and García‐Plazaola , Smerilli et al. ). Xanthophyll cycle‐mediated NPQ is also determined by the QE of the de‐epoxidized xanthophylls.…”
Xanthophyll cycle‐related nonphotochemical quenching (NPQ), which is present in most photoautotrophs, allows dissipation of excess light energy. Xanthophyll cycle‐related NPQ depends principally on xanthophyll cycle pigments composition and their effective involvement in NPQ. Xanthophyll cycle‐related NPQ is tightly controlled by environmental conditions in a species‐/strain‐specific manner. These features are especially relevant in microalgae living in a complex and highly variable environment. The goal of this study was to perform a comparative assessment of NPQ ecophysiologies across microalgal taxa in order to underline the specific involvement of NPQ in growth adaptations and strategies. We used both published results and data acquired in our laboratory to understand the relationships between growth conditions (irradiance, temperature, and nutrient availability), xanthophyll cycle composition, and xanthophyll cycle pigments quenching efficiency in microalgae from various taxa. We found that in diadinoxanthin‐containing species, the xanthophyll cycle pigment pool is controlled by energy pressure in all species. At any given energy pressure, however, the diatoxanthin content is higher in diatoms than in other diadinoxanthin‐containing species. XC pigments quenching efficiency is species‐specific and decreases with acclimation to higher irradiances. We found a clear link between the natural light environment of species/ecotypes and quenching efficiency amplitude. The presence of diatoxanthin or zeaxanthin at steady state in all species examined at moderate and high irradiances suggests that cells maintain a light‐harvesting capacity in excess to cope with potential decrease in light intensity.
“…When cell concentrations at T f were not significantly different between controls and copepod tanks, grazing was considered under the detection limit (i.e., <dl in Table 4). Ingestion rates were converted to ng Chl a ind −1 d −1 using a literature-based mean value of 0.10 pg Chl a cell −1 for S. marinoi (Norici et al, 2011;Chandrasekaran et al, 2014;Orefice et al, 2016;Smerilli et al, 2019) and 0.35 pg Chl a cell −1 for C. neogracile (unpublished data from González-Fernández et al, 2019).…”
Section: Specific Growth Rate and Grazing Parametersmentioning
In marine ecosystems, carbon export is driven by particle flux which is modulated by aggregation, remineralization, and grazing processes. Zooplankton contribute to the sinking flux through the egestion of fast sinking fecal pellets but may also attenuate the flux by tearing apart phytoplankton aggregates into small pieces through swimming activity or direct ingestion. Freely suspended cells, artificial monospecific aggregates from two different diatom species (Chaetoceros neogracile and Skeletonema marinoi) and natural aggregates of Melosira sp. were independently incubated with five different copepod species (Acartia clausi, Temora longicornis, Calanus helgolandicus, Euterpina acutifrons, and Calanus hyperboreus). During the grazing experiments initiated with free diatoms, E. acutifrons feeding activity evidenced by ingestion rates of 157 ± 155 ng Chl a ind −1 d −1 , induced a significant increase of S. marinoi aggregation. Transparent exopolymeric particles (TEP) production was only slightly boosted by the presence of grazers and turbulences created by swimming may be the main trigger of the aggregation processes. All copepods studied were able to graze on aggregates and quantitative estimates led to chlorophyll a ingestion rates (expressed in Chla a equivalent, i.e., the sum of chlorophyll a and pheopigments in their guts) ranging from 4 to 23 ng Chl a eq ind −1 d −1 . The relation between equivalent spherical diameters (ESDs) and sinking velocities of the aggregates did not significantly change after grazing, suggesting that copepod grazing did not affect aggregate density as also shown by Si:C and C:N ratios. Three main trends in particle dynamics could be identified and further linked to the copepod feeding behavior and the size ratio between prey and predators:(1) Fragmentation of S. marinoi aggregates by the cruise feeder T. longicornis and of Melosira sp. aggregates by C. hyperboreus at prey to predator size ratios larger than 15; (2) no change of particle dynamics in the presence of the detritic cruise feeder E. acutifrons; and finally (3) re-aggregation of C. neogracile and S. marinoi aggregates when the two filter feeders A. clausi and C. helgolandicus were grazing on aggregate at prey to predator size ratios lower than 10. Aggregation of freely suspended cells or small aggregates was facilitated by turbulence resulting from active swimming of small copepods. However, stronger turbulence created by larger cruise feeders copepods prevent aggregate formation and even made them vulnerable to breakage.
“…The content in the other vitamins, generally provided by higher plants, can be also significant if we consider that are unicellular organisms. For instance, the green microalga Dunaliella is known to highly accumulate the vitamins B 2 , B 12 , B 9 , B 3 as well as the vitamins C and E [ 11 ] while high content of vitamin C has been reported in the diatom Skeletonema marinoi [ 12 , 13 ]. Fig.…”
Background
Vitamins’ deficiency in humans is an important threat worldwide and requires solutions. In the concept of natural biofactory for bioactive compounds production, microalgae represent one of the most promising targets filling many biotechnological applications, and allowing the development of an eco-sustainable production of natural bioactive metabolites. Vitamins are probably one of the cutting edges of microalgal diversity compounds.
Main text
Microalgae can usefully provide many of the required vitamins in humans, more than terrestrial plants, for instance. Indeed, vitamins D and K, little present in many plants or fruits, are instead available from microalgae. The same occurs for some vitamins B (B12, B9, B6), while the other vitamins (A, C, D, E) are also provided by microalgae. This large panel of vitamins diversity in microalgal cells represents an exploitable platform in order to use them as natural vitamins’ producers for human consumption. This study aims to provide an integrative overview on vitamins content in the microalgal realm, and discuss on the great potential of microalgae as sources of different forms of vitamins to be included as functional ingredients in food or nutraceuticals for the human health. We report on the biological roles of vitamins in microalgae, the current knowledge on their modulation by environmental or biological forcing and on the biological activity of the different vitamins in human metabolism and health protection.
Conclusion
Finally, we critically discuss the challenges for promoting microalgae as a relevant source of vitamins, further enhancing the interests of microalgal “biofactory” for biotechnological applications, such as in nutraceuticals or cosmeceuticals.
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