Claire Berkaloff

Chemical evidence of kerogen formation in source rocks and oil shales via selective preservation of thin resistant outer walls of microalgae: Origin of ultralaminae

Abstract New structures, termed ultralaminae, were recently observed by Transmission Electron Microscopy, usually in high amounts, in a number of kerogens from oil shales and source rocks. Morphological similarities were noted between ultralaminae and the thin (ca. 15 nm) resistant outer walls, composed of non-hydrolyzable macromolecules (algaenans), commonly occurring in extant Chlorophyceae, especially in the cosmopolitan genus Scenedesmus . Identification of the pyrolysis products of S. quadricauda algaenan showed (i) a highly aliphatic structure based on a macromolecular network of long (up to C 32 ) polymethylenic chains probably cross-linked by ether bridges, and (ii) a close correlation based on the formation of n- alkylnitriles , between this algaenan and two ultralaminar kerogens, the Rundle Oil Shale (mainly composed of ultralamina accumulations) and the Green River Shale (ultralaminae dispersed within an amorphous matrix). These fossil ultralaminae, therefore, likely originated from the selective preservation of the thin, algaenan-containing, outer walls of Scenedesmus and/or of other Chlorophyceae containing outer walls of a similar morphology and composition. Relative distributions of n- alkylnitriles and of n- alkanoic acids, in the pyrolysates of S. quadricauda algaenan and of the Rundle Oil Shale, indicated that nitriles are not derived from secondary reactions of carboxylic acids but originate from preexisting nitrogen functions, likely amides. Previous evidence of kerogen formation via selective preservation of algaenans was restricted to rather uncommon kerogens; the present results, added to ultralamina common occurrence and abundance, point to a wide involvement and to a large contribution of the selective preservation of algaenan-containing thin outer walls of Chlorophyceae in the formation of kerogens in a number of lacustrine source rocks and oil shales. All the available information suggest that the three-way correlation (selective preservation of algaenans from thin resistant chlorophycean outer walls, formation of fossil ultralaminae, presence of n- alkylnitriles with a typical distribution in the pyrolysates of ultralaminar kerogens) observed in this study might be of a general character.

Subunit organization of PSI particles from brown algae and diatoms: polypeptide and pigment analysis.

P700 enriched fractions were isolated from two brown algae and one diatom using sucrose density centrifugation after digitinin solubilization. They had a Chl a/P700 ratio of about 250 to 375 according to the species, they were enriched in long-wavelength absorbing Chl a and exhibited a fluorescence emission maximum at 77 K near 720 nm. They all presented a major polypeptide component at 66±2 kDa, but their polypeptide composition was rather complex and somewhat different from one species to another. Further solubilization with dodecylmaltoside of those ‘native’ PSI particles allowed the separation of two or three fractions. The lightest, xanthophyll-rich, fraction was identified to be a light-harvesting complex. It contained no P700 and had a major polypeptide of molecular weight near 20 kDa (at the same molecular weight than the respective LH ‘native’ fraction of each species) and exhibited a 77 K peak fluorescence emission at 685 nm. The other fractions were enriched in P700 and almost entirely depleted in xanthophylls. When two of them are present, they both exhibited a major polypeptide at 66±2 kDa and were totally devoid of the LH polypeptide, but the two fractions widely differed one from another in the abundance and molecular weight of the other polypeptide components. The most purified of these two fractions presented a composition similar to PSI core complex from green plants.

Changes in yield ofin-vivo fluorescence of chlorophyll a as a tool for selective herbicide monitoring

Triazines and derivatives of phenylurea, which are often found in outdoor water samples, induce specific changes in the yield of thein-vivo chlorophyll α-fluorescence of PSII. These changes are correlated quantitatively with the concentration of the herbicides and can therefore be used to set-up a low-price monitor system. In order to detect selectively the herbicide-sensitive part of the fluorescence emission a pulse amplitude modulated fluorimeter was used. The bioassay system was optimised with respect to test organism, growing and measuring conditions. The relationship between fluorescence yield and herbicide concentrations were experimentally determined for the triazines atrazine and simazine and the phenylurea herbicide DCMU and mathematically fitted (r=0.99). The I50-values were 0.9 µM for DCMU, 2.2 µM for simazine and 3.3 µM for atrazine. The detection limit of about 0.5 µM clearly shows that the sensitivity of this bioassay system is too low to reach the requirements of the drinking water regulation. However, due to its insensitivity against complex water matrices, there is good hope to combine this fluorometric bioassay with a potent herbicide preconcentration method like a solid-phase extraction procedure.

Effects of high light and desiccation on the operation of the xanthophyll cycle in two marine brown algae

Two brown algae, Pelvetia canaliculata and Laminaria saccharina, from the higher and lower mediolittoral belts respectively, have been tested for their capacity to overcome high-light stress in water and in air (in both fully hydrated and desiccated states). When exposed to supersaturating light irradiance in water, the two species developed non-photochemical quenching of fluorescence (NPQ) which was correlated with an increase in the de-epoxidation ratio (DR) of the xanthophyll cycle carotenoids (violaxanthin, antheraxanthin and zeaxanthin) and was followed by a slower decrease in oxygen evolution. NPQ reached values of up to 9 in P. canaliculata but only 4·5 in L. saccharina, at DRs of 0·65 and 0·5, respectively. In air, the xanthophyll cycle was also operative but the efficiency of de-epoxidation decreased linearly with the degree of hydration of the thallus. Photoprotection capacities in air also appeared higher in P. canaliculata than in L. saccharina, probably due to the higher molar content of the ...

Gene structure of a chlorophyll a/c-binding protein from a brown alga : presence of an intron and phylogenetic implications

ALaminaria saccharina genomic library in the phage EMBL 4 was used to isolate and sequence a full-length gene encoding a fucoxanthin-chlorophyll a/c-binding protein. Contrary to diatom homologues, the coding sequence is interrupted by an intron of about 900 bp which is located in the middle of the transit peptide. The deduced amino acid sequence of the mature protein is very similar to those of related proteins fromMacrocystis pyrifera (Laminariales) and, to a lesser extent, to those from diatoms and Chrysophyceae. Seven of the eight putative chlorophyll-binding amino acids determined in green plants are also present.Alignments of different sequences related to the light-harvesting proteins (LHC) demonstrate a structural similarity among the three transmembrane helices and suggest a unique ancestral helix preceded by two β-turns. The β-turns are conserved in front of the second helices of the chlorophyll a/c proteins more so than in chlorophyll a/b proteins.Phylogenetic trees generated from sequence data indicate that fucoxanthin-chlorophyll-binding proteins diverged prior to the separation of photosystem I and photosystem II LHC genes of green plants. Among the fucoxanthin-containing algae, LHC I or II families could not be distinguished at this time.

Polypeptide composition of light-harvesting complexes from some brown algae and diatoms

The polypeptide composition of some Chromophyte light‐harvesting complexes was investigated by SDS‐PAGE and compared to LHCP of higher plants. According to the species, one or two major polypeptides were found in the range 17–25 kDa, which is noticeably lower than for higher plant LHCP polypeptides. Evidence is provided for three species LH polypeptides possessing different molecular masses that they all possess some immunological analogy with a maize LHCP. In addition, Fucus serratus LH was proved to be able to phosphorylate.

Chlorophyll fluorescence transients from the diatom Phaeodactylum tricornutum: relative rates of cyclic phosphorylation and chlororespiration

In Phaeodactylum tricornutum cells kept 30 min in the dark, induction of fluorescence showed the well-known levels OIDPSMT. The decrease of MT was the most important when the intensity of excitation light was high. It was mainly due to the photochemical quenching. After addition of DCMU (2 to 20 μM), a quenching qE was still observed: this quenching, cancelled by NH4Cl (2 to 20 mM) is attributed to ΔpH. This qE was also inhibited by antimycin, an inhibitor of cyclic phosphorylation and may be of chlororespiration above plastoquinones. Anaerobiosis also decreased it. We can infer that chlororespiration also plays a part in the formation of the ΔpH in the presence of DCMU. After 30 mn of preillumination in red light, the levels P and M were lower and the quenching in presence of DCMU was no more observed: thus, neither the chlororespiration nor the cyclic phosphorylation were active, unless the activity of ATPase was much more important. So, in diatoms, one at least of the above cited phenomena can be modulated by light.

Immobilization of Botryococcus braunii in alginate: influence on chlorophyll content, photosynthetic activity and degeneration during batch cultures

SummaryImmobilization of the hydrocarbonrich microalga Botryococcus braunii in calcium alginate beads results in a large increase in chlorophyll content and chlorophyll photosynthetic activity, relative to free cells, at any stage of standard batch cultures. Immobilization exerts a protective influence on ageing cultures both under standard and air lift conditions. Decreases in chlorophyll content and photosynthetic activity are delayed and slowed down; the organization of protein-chlorophyll complexes is stabilized. These positive effects are related to protection of entrapped cells against photoinhibition owing to gel screening and self-shadowing.Entrapped cells show also, immediately after immobilization, a higher photosynthetic activity than free controls. The unusually high activity yield thus achieved probably results from increase in ionic concentration in the microenvironment of B. braunii.

FREEZE FRACTURE STUDY OF THYLAKOIDS OF FUCUS SERRATUS1

Freeze‐fractured thylakoids of Fucus serratus L. exhibit three types of faces with a particle density analogous to that of EFs, EFu and PF faces of green plants. However the particle size distribution is unimodal in the three types with a mean of about 8 nm. No obvious distinction between PFs and PFu faces could be detected. The absence on EFs faces of the distinct class of large particles (>13 nm) existing in green plant thylakoids implies a unique organization of pigment proteins, especially of the light‐harvesting complexes.

Isolation and characterization of PSII core complexes from a brown alga, Laminaria saccharina

PSII‐enriched particles, active for DCIP‐reduction, were prepared from Laminaria saccharina chloroplasts, and PSII core complexes were further purified by ion‐exchange chromatography. They contained several polypeptides, four of them cross‐reacting with antibodies raised against CP47, CP43, D1 and D2 of green plants. A second chromatography was required to separate: (i) a core antenna, composed of 51 kDa polypeptide subunits, binding 11 β‐carotene, 4 chlorophyll (Chl) c and 7 fucoxanthin for 100 Chl a, and reacting with CP47 antibodies; and (ii) a reaction center complex consisting of two main polypeptides of 34 and 36 kDa. The pigment stoichiometry was of 5 Chl a and 0.5 β‐carotene for 2 pheophytin a. The 34 and 36 kDa components cross‐reacted with anti‐D1 and anti‐D2 antibodies, respectively. The presence of cytochrome b‐559 was substantiated by spectrophotometry.