E. Casadevall

Sites of accumulation and composition of hydrocarbons in Botryococcus braunii

Abstract Raman spectrometry and electron microscopy show that, in the hydrocarbon-rich alga Botryococcus braunii , hydrocarbons accumulate in two distinct sites; internally in cytoplasmic inclusions and externally in successive outer walls and derived globules. No other classes of lipid are present in noticeable amounts in the cytoplasmic inclusions and in the external globules. The same hydrocarbons are observed in the internal and external pools but with different relative abundances, the shorter hydrocarbons being more abundant in the internal pool. The bulk of B. braunii hydrocarbons ( ca 95%) is located in the external pool. Such an extracellular location allows this species to exhibit both an unusually high hydrocarbon content (15% of dry wt) and a normal level (0.75%) within the cells. The hydrocarbon pattern and location of B. braunii were compared with that of other organisms; a close relation appears between higher plant epidermal cells and this green alga. The trilaminar outer walls of B. braunii , at whose contact external hydrocarbon globules accumulate, contain a sporopollenin-like compound.

Pyrolysis of immature Torbanite and of the resistant biopolymer (PRB A) isolated from extant alga Botryococcus braunii. Mechanism of formation and structure of torbanite

Abstract Immature Torbanite and the resistant biopolymer (PRB A ) isolated from extant B. braunii were previously compared using bulk spectroscopic methods. In the present work, analysis of 400°C pyrolysis products and pyrolysis residues provided further information on their structure and possible relationships. It appears that such polymers are based upon unbranched, saturated, cross-linked hydrocarbon chains up to C 31 . In addition to these bridging structures, a substantial part of the alkyl chains is singly bound, as esters of unbranched, saturated or cis unsaturated, even fatty acids. These esters are sterically protected, against chemical degradations, by the network of the bioand geopolymer. Quantitative and qualitative observations derived from 400°C pyrolysis confirm that the chemical structure of PRB A and immature Torbanite are closely related. The pyrolysis residues show a similar evolution and numerous common features are noted, with respect to the nature and the distribution of the major constituents of the pyrolysates (hydrocarbons and fatty acids). Accordingly, Botryococcus provides what seems to be the first example of a close structural relationship between a biopolymer produced in large amounts by an extant alga and the geopolymer of an immature kerogen. The essential role of PRB A in Torbanite formation is ascertained. Moreover, it is found that the resistant biopolymer does not undergo important structural changes during the first stages of diagenesis. Thus, owing to steric protection, the esters of immature Torbanite show a distribution quite close to the one of PRB A esters, with exclusively even constituents and a large contribution of unsaturated acids. Recent observations pointed to the possible genesis of some algal kerogens principally by selective preservation of resistant macromolecules. Such a type of formation is clearly predominant in Torbanite, where the bulk of the fossil organic matter corresponds to a selectively preserved and weakly altered, resistant biopolymer, while incorporation of lipids into the kerogen structure during diagenesis seems to play a minor role.

Alkadiene- and botryococcene-producing races of wild strains of Botryococcus braunii

Abstract Samples of the green colonial alga Botryococcus braunii, collected from various localities, were grown in the laboratory and examined for their hydrocarbon content and morphology. Although few differences appeared between the ultrastructures of the samples, the nature of their hydrocarbons, which remains unchanged at any stage of growth, allows the distinction of two physiological races viz algae producing odd-numbered unbranched alkadienes and trienes (C25C31) (the A race) and those producing polymethylated triterpenes CnH2n-10 (C30C37), the botryococcenes (the B race). In laboratory culture, the hydrocarbon content of these new strains is very high, from 30 to 60% of the dry biomass. For the two races the greatest hydrocarbon productivity takes place during the active growth phase. The important variability observed in botryococcene distribution could originate both from genetic and environmental factors.

Formation of Botryococcus-derived kerogens—Comparative study of immature torbanites and of the extent alga Botryococcus braunii

The outer walls of the extant alga Botryococcus braunii were shown to contain large amounts of a biopolymer, termed PRB (Polymere Resistant de Botryococcus), characterized by a very high resistance towards chemical attacks. Such features suggested that PRB could play a prominent role in the formation of Botryococcus-derived kerogens. In the present work we examined the structure and the origin of PRB using i.r., 13CNMR, pyrolysis-GC and feeding experiments. It appears that PRB synthesized by the living alga comprises chiefly long unbranched, or weakly branched, hydrocarbon chains (containing some cis unsaturations, OH and ester function) probably linked by ether bridges. This biopolymer derives from the dienic hydrocarbons occuring in high level in the alga, or from some long chain close precursors of the latter. A comparative study of PRB with Coorongite and immature Torbanites (i.r., 13CNMR, H/C and O/C atomic ratios, preliminary results from pyrolysis-GC) indicates that PRB is very likely the major constituent of the initial biomass from which Botryococcus-derived kerogens were built. The biosynthesis of PRB by B. braunii accounts for the efficiency of this alga to produce large amounts of kerogens with a high oil potential.

Lycopadiene, a tetraterpenoid hydrocarbon from new strains of the green alga Botryococcus braunii

Abstract Lycopadiene (2,6R,10R,14,19,23R,27R,31 -octamethyldotriaconta- 14(E), 18(E)-diene) has been isolated from the hexane extract of new strains of the green colonial alga Botryococcus braunii . Synthesized in relatively high amount, up to 8% of dry wt, this tetraterpene could be a precursor of lycopane found in some recent and ancient sediments.

Structures of some botryococcenes: branched hydrocarbons from the b-race of the green alga Botryococcus braunii

Nine branched hydrocarbons of the botryococcene type (CnH2n-10 30 ⩽ n ⩽ 37) have been isolated from the green alga Botryococcus braunii. Hydrocarbon mixtures were recovered from wild algae collected in fresh water lakes or from the same strains growing in laboratory; they were further separated by reversed-phase, and in some cases by normal phase, HPLC. From chemical investigations, GC/MS analyses, 1H and 13C NMR spectroscopy, the structures of four new botryococcenes (one C33H56, two C34H58 and one C37H64) were elucidated.

Resistant biopolymer in the outer walls of Botryococcus braunii, B race

Abstract A biopolymer highly resistant to non-oxidative treatments (PRB B ) occurs in the outer walls of the B race of Botryococcus braunii . PRB B accounts for ca 10% of the total algal biomass and fulfils the usual requirements to be regarded as a sporopollenin; however, the structural information obtained indicate it does not derive from carotenoids. A complete lack of relationship was also noted between PRB B and the isoprenoid hydrocarbons produced in large amount by the B race. The PRB B structure is based upon saturated, normal, hydrocarbon chains up to C 31 ; these chains are probably linked by ether bridges. PRB B also comprises ester and hydroxyl groups protected from external attacks by the polymeric network. PRB B and PRB A (the resistant biopolymer isolated from the outer walls of the A race of B. braunii , which produces non-isoprenoid hydrocarbons) are not identical. Nevertheless they show the same major structural features and belong to the samegroup of resistant biopolymers (probably derived from the polymerisation of very long chain fatty acid derivatives). Analogies between PRB A and PRB B would have resulted in the formation, via fossilization of A and B races, of kerogens with a similar structure and a high oil potential.

Occurrence of a resistant biopolymer in the L race of Botryococcus braunii

Abstract A resistant biopolymer, PRB L , occurs in the outer walls of the L race of Botryococcus braunii . It accounts for a larger fraction of the total biomass than PRB A and B do in the A and B races. The PRB L structure is mainly based on long (up to C 30 saturated, isoprenoid hydrocarbon chains probably linked by ether bridges. Most of these isoprenoid chains exhibit regular head-to-tail linkages. Therefore, PRB L does not belong to the same family as PRB A and B , the structures of which are based on long, normal hydrocarbon chains. The only hydrocarbon produced by the L race algae is a lycopadiene so a relationship between hydrocarbon and PRB structure can be considered in this L race as has already been demonstrated for the A race.

Characterization of Estonian Kukersite by spectroscopy and pyrolysis: Evidence for abundant alkyl phenolic moieties in an Ordovician, marine, type II/I kerogen

Abstract The kerogen of a sample of Estonian Kukersite (Ordovician) was examined by spectroscopic (solid state 13C NMR, FTIR) and pyrolytic (“off-line”, flash) methods. This revealed an important contribution of long, linear alkyl chains in Kukersite kerogen. The hydrocarbons formed upon pyrolysis are dominated by n-alkanes and n-alk-1-enes and probably reflect a major contribution of selectivity preserved, highly aliphatic, resistant biomacromolecules from the outer cell walls of Gloeocapsomorpha prisca. This is consistent with the abundant presence of this fossilized organism in Kukersite kerogen. In addition high amounts of phenolic compounds were identified in the pyrolysates. Series of non-methylated, mono-, di- and trimethylated 3-n-alkylphenols, 5-n-alkyl-1,3-benzenediols and n-alkylhydroxybenzofurans were identified. All series of phenolic compounds contain long (up to C19), linear alkyl side-chains. Kukersite kerogen is, therefore, an aliphatic type II/I kerogen, despite the abundance of free phenolic moieties. This study shows that phenol-derived moieties are not necessarily associated with higher plant-derived organic matter. The flash pyrolysate of Kukersite kerogen was also compared with that of the kerogen of the Guttenberg Oil Rock (Ordovician) which is also composed of accumulations of fossilized G. prisca. Similarities in the distributions of hydrocarbons and sulphur compounds were noted, especially for the C1–C6 alkylbenzene and alkylthiophene distributions. However, no phenolic compounds were detected in the flash pyrolysate of the Guttenberg kerogen. Possible explanations for the observed similarities and differences are discussed.

Occurrence and origin of «ultralaminar» structures in «amorphous» kerogens of various source rocks and oil shales

Abstract Forty low maturity, type I–II kerogens from source rocks and oil shales, ranging in age from Infra-Cambrian to Miocene, were examined by transmission electron microscopy (TEM). When previously observed by light microscopy and/or UV fluorescence microscopy the above samples, like a very large number of kerogens, seemed homogeneous and amorphous. In fact, TEM revealed the presence of “ultralaminar” structures in 22 of these “amorphous” kerogens. The abundance of “ultralaminae” depends on the considered sample and some of the tested kerogens are nearly exclusively composed of “ultralamina” accumulations. Based on thickness, three main groups of “ultralaminae” can be identified. Parallel studies on extant algae indicated that some of the above “ultralaminae” likely derived from the resistant outer walls of microalgae. The fossilization of such outer walls should occur via the “selective preservation” pathway and result in the formation of highly aliphatic “ultralaminar” kerogens. The lack of “ultralaminae” in Infra-Cambrian kerogens is consistent with a cyanobacterial origin.