Seawater carbonate chemistry and physiological response of the Mediterranean crustose coralline alga Lithophyllum cabiochae to elevated pCO2 and temperature

The response of respiration, photosynthesis, and calcification to elevated pCO2 and temperature was investigated in isolation and in combination in the Mediterranean crustose coralline alga Lithophyllum cabiochae. Algae were maintained in aquaria during 1 year at near-ambient conditions of irradiance, at ambient or elevated temperature (+3 °C), and at ambient (ca. 400 µatm) or elevated pCO2 (ca. 700 µatm). Respiration, photosynthesis, and net calcification showed a strong seasonal pattern following the seasonal variations of temperature and irradiance, with higher rates in summer than in winter. Respiration was unaffected by pCO2 but showed a general trend of increase at elevated temperature at all seasons, except in summer under elevated pCO2. Conversely, photosynthesis was strongly affected by pCO2 with a decline under elevated pCO2 in summer, autumn, and winter. In particular, photosynthetic efficiency was reduced under elevated pCO2. Net calcification showed different responses depending on the season. In summer, net calcification increased with rising temperature under ambient pCO2 but decreased with rising temperature under elevated pCO2. Surprisingly, the highest rates in summer were found under elevated pCO2 and ambient temperature. In autumn, winter, and spring, net calcification exhibited a positive or no response at elevated temperature but was unaffected by pCO2. The rate of calcification of L. cabiochae was thus maintained or even enhanced under increased pCO2. However, there is likely a trade-off with other physiological processes. For example, photosynthesis declines in response to increased pCO2 under ambient irradiance. The present study reports only on the physiological response of healthy specimens to ocean warming and acidification, however, these environmental changes may affect the vulnerability of coralline algae to other stresses such as pathogens and necroses that can cause major dissolution, which would have critical consequence for the sustainability of coralligenous habitats and the budgets of carbon and calcium carbonate in coastal Mediterranean ecosystems.

Arsenic speciation in edible alga samples by microwave-assisted extraction and high performance liquid chromatography coupled to atomic fluorescence spectrometry

Twelve commercially available edible marine algae from France, Japan and Spain and the certified reference material (CRM) NIES No. 9 Sargassum fulvellum were analyzed for total arsenic and arsenic species. Total arsenic concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after microwave digestion and ranged from 23 to 126 μg g−1. Arsenic species in alga samples were extracted with deionized water by microwave-assisted extraction and showed extraction efficiencies from 49 to 98%, in terms of total arsenic. The presence of eleven arsenic species was studied by high performance liquid chromatography–ultraviolet photo-oxidation–hydride generation atomic–fluorescence spectrometry (HPLC–(UV)–HG–AFS) developed methods, using both anion and cation exchange chromatography. Glycerol and phosphate sugars were found in all alga samples analyzed, at concentrations between 0.11 and 22 μg g−1, whereas sulfonate and sulfate sugars were only detected in three of them (0.6-7.2 μg g−1). Regarding arsenic toxic species, low concentration levels of dimethylarsinic acid (DMA) (<0.9 μg g−1) and generally high arsenate (As(V)) concentrations (up to 77 μg g−1) were found in most of the algae studied. The results obtained are of interest to highlight the need to perform speciation analysis and to introduce appropriate legislation to limit toxic arsenic species content in these food products.

The heme oxygenase gene (pbsA) in the red alga Rhodella violacea is discontinuous and transcriptionally activated during iron limitation

Heme oxygenase (HO) catalyzes the opening of the heme ring with the release of iron in both plants and animals. In cyanobacteria, red algae, and cryptophyceae, HO is a key enzyme in the synthesis of the chromophoric part of the photosynthetic antennae. In an attempt to study the regulation of this key metabolic step, we cloned and sequenced the pbsA gene encoding this enzyme from the red alga Rhodella violacea. The gene is located on the chloroplast genome, split into three distant exons, and is presumably expressed by a trans-splicing mechanism. The deduced polypeptide sequence is homologous to other reported HOs from organisms containing phycobilisomes (Porphyra purpurea and Synechocystis sp. strain PCC 6803) and, to a lesser extent, to vertebrate enzymes. The expression is transcriptionally activated under iron deprivation, a stress condition frequently encountered by algae, suggesting a second role for HO as an iron-mobilizing agent in photosynthetic organisms.

Gene replacement by homologous recombination in the multicellular green alga Volvox carteri

With only two different cell types, the haploid green alga Volvox represents the simplest multicellular model system. To facilitate genetic investigations in this organism, the occurrence of homologous recombination events was investigated with the intent of developing methods for gene replacement and gene disruption. First, homologous recombination between two plasmids was demonstrated by using overlapping nonfunctional fragments of a recombinant arylsulfatase gene (tubulin promoter/arylsulfatase gene). After bombardment of Volvox reproductive cells with DNA-coated gold microprojectiles, transformants expressing arylsulfatase constitutively were recovered, indicating the presence of the machinery for homologous recombination in Volvox. Second, a well characterized loss-of-function mutation in the nuclear nitrate reductase gene (nitA) with a single G → A nucleotide exchange in a 5′-splice site was chosen as a target for gene replacement. Gene replacement by homologous recombination was observed with a reasonably high frequency only if the replacement vector containing parts of the functional nitrate reductase gene contained only a few nucleotide exchanges. The ratio of homologous to random integration events ranged between 1:10 and 1:50, i.e., homologous recombination occurs frequently enough in Volvox to apply the powerful tool of gene disruption for functional studies of novel genes.

A Model for Signal Transduction during Gamete Release in the Fucoid Alga Pelvetia compressa1

Fucoid algae release gametes into seawater following an inductive light period (potentiation), and gamete expulsion from potentiated receptacles of Pelvetia compressa began about 2 min after a light-to-dark transition. Agitation of the medium reversed potentiation, with an exponential time course completed in about 3 h. Light regulated two signaling pathways during potentiation and gamete expulsion: a photosynthetic pathway and a photosynthesis-independent pathway in which red light was active but blue light was not. Uptake of K+ appears to have an important role in potentiation, because a 50% inhibition of potentiation occurred in the presence of the tetraethylammonium ion, a K+-channel blocker. A central role of anion channels in the maintenance of potentiation is suggested by the premature release of gametes in the light when receptacles were incubated with inhibitors of slow-type anion channels. An inhibitor of tyrosine kinases, tyrphostin A63, also inhibited potentiation. A model for gamete release from P. compressa is presented that proposes that illumination results in the accumulation of ions (e.g. K+) throughout the cells of the receptacle during potentiation, which then move into the extracellular matrix during gamete expulsion to generate osmomechanical force, resulting in gamete release.

Intracellular β-Carbonic Anhydrase of the Unicellular Green Alga Coccomyxa1 : Cloning of the cDNA and Characterization of the Functional Enzyme Overexpressed in Escherichia coli

Carbonic anhydrase (CA) (EC 4.2.1.1) enzymes catalyze the reversible hydration of CO2, a reaction that is important in many physiological processes. We have cloned and sequenced a full-length cDNA encoding an intracellular β-CA from the unicellular green alga Coccomyxa. Nucleotide sequence data show that the isolated cDNA contains an open reading frame encoding a polypeptide of 227 amino acids. The predicted polypeptide is similar to β-type CAs from Escherichia coli and higher plants, with an identity of 26% to 30%. The Coccomyxa cDNA was overexpressed in E. coli, and the enzyme was purified and biochemically characterized. The mature protein is a homotetramer with an estimated molecular mass of 100 kD. The CO2-hydration activity of the Coccomyxa enzyme is comparable with that of the pea homolog. However, the activity of Coccomyxa CA is largely insensitive to oxidative conditions, in contrast to similar enzymes from most higher plants. Fractionation studies further showed that Coccomyxa CA is extrachloroplastic.

Purification and Characterization of Phosphoribulokinase from the Marine Chromophytic Alga Heterosigma carterae1

In this study we characterized phosphoribulokinase (PRK, EC 2.7.1.19) from the eukaryotic marine chromophyte Heterosigma carterae. Serial column chromatography resulted in approximately 300-fold purification of the enzyme. A polypeptide of 53 kD was identified as PRK by sequencing the amino terminus of the protein. This protein represents one of the largest composite monomers identified to date for any PRK. The native holoenzyme demonstrated by flow performance liquid chromatography a molecular mass of 214 ± 12.6 kD, suggesting a tetrameric structure for this catalyst. Because H. carterae PRK activity was insensitive to NADH but was stimulated by dithiothreitol, it appears that the enzyme may require a thioredoxin/ferredoxin rather than a metabolite mode of regulation. Kinetic analysis of this enzyme demonstrated Michaelis constant values of ribulose-5-phosphate (226 μm) and ATP (208 μm), respectively. In summary, H. carterae PRK is unique with respect to holoenzyme structure and function, and thus may represent an alternative evolutionary pathway in Calvin-cycle kinase development.

Induced β-Carotene Synthesis Driven by Triacylglycerol Deposition in the Unicellular Alga Dunaliella bardawil1

Under stress conditions such as high light intensity or nutrient starvation, cells of the unicellular alga Dunaliella bardawil overproduce β-carotene, which is accumulated in the plastids in newly formed triacylglycerol droplets. We report here that the formation of these sequestering structures and β-carotene are interdependent. When the synthesis of triacylglycerol is blocked, the overproduction of β-carotene is also inhibited. During overproduction of β-carotene no up-regulation of phytoene synthase or phytoene desaturase is observed on the transcriptional or translational level, whereas at the same time acetyl-CoA carboxylase, the key regulatory enzyme of acyl lipid biosynthesis, is increased, at least in its enzymatic activity. We conclude that under normal conditions the carotenogenic pathway is not maximally active and may be appreciably stimulated in the presence of sequestering structures, creating a plastid-localized sink for the end product of the carotenoid biosynthetic pathway.

Avaliação do potencial fotoprotetor e identificação de metabólitos secundários do fungo endofítico Annulohypoxylon stygium associado à alga marinha Bostrychia radicans

Os organismos marinhos constituem uma fonte potencial de metabólitos secundários biologicamente ativos. Neste contexto, os micro-organismos isolados de algas marinhas, dentre eles fungos endofíticos, representam alvos para a pesquisa de novas substâncias com potencial farmacológico pronunciado. Substâncias naturais provenientes de espécies de fungos associados às algas marinhas vêm sendo bastante utilizadas em formulações fotoprotetoras devido à ação antioxidante e ao potencial contra a radiação solar. Deste modo, o presente trabalho teve como objetivo a investigação biológica e química dos fungos endofíticos marinhos pertencentes à família Xylariaceae, o Annulohypoxylon stygium, o Cladosporium sp. e o Acremonium implicatum (Hypocreaceae). A princípio, foi realizado um screening para avaliar a absorção de luz ultravioleta na faixa do UVA e UVB pelos extratos obtidos em escala piloto destes fungos endofíticos associados às algas marinhas. O extrato do fungo A. stygium apresentou intensa absorção na região do UV, mostrando-se promissor para a produção de metabólitos secundários com ação fotoprotetora. Além do ensaio proposto, foi realizada a avaliação do potencial antibacteriano e antifúngico da espécie A. stygium. O estudo químico em escala ampliada deste fungo proporcionou o isolamento e identificação de uma substância inédita da classe derivada da 2,5- dicetopiperazina, 3-benzilideno-2-metil-hexahidro-pirrolo [1,2-?] pirazina-1,4-diona (Sf3), e além desta, foram isolados mais quatro metabólitos como, os diasteroisômeros 1-fenil-1,2- propanediol (Sd2) e 1-fenil-1,2-propanediol (Sd3), 1,3-benzodioxole-5-metanol (Sc1), 1,2- propanodiol-1-(1,3-benzodioxol-5-il) (Se1). Ainda foi possível a desreplicação de substâncias via cromatografia gasosa acoplada à espectrometria de massas (CG-EM), entre elas o ácido palmítico, palmitato de metila, ácido metil linoléico, ácido oléico, álcool benzílico e o piperonal. Quanto ao estudo da atividade biológica, não foi observado potencial antibacteriano e antifúngico para os extratos e frações do fungo. Entretanto, notouse um potencial como fotoprotetor in vitro para as frações n-Hexano/AcOEt (2:3) e n- Hexano/AcOEt (1:4) obtidas a partir do extrato do cultivo de 28 dias do fungo A. stygium, extraído com solventes diclorometano/metanol (CH2Cl2/MeOH 2:1) e para a substância (Sf3) isolada do mesmo. Desta forma, o estudo químico e biológico do fungo Annulohypoxylon stygium demonstrou potencial para a produção de metabólitos secundários com atividade fotoprotetora, visto que uma estrutura inédita com esta atividade foi isolada e identificada como produto natural.

Notes on the Siluro-Devonian Ischadites stellatus (Fagerstrom 1961), a Dasycladaceous Alga / [by] Matthew H. Nitecki.

v.23:no.3(1971)