Béatrice Allard

Comparison of neutral lipid profile of various trilaminar outer cell wall (TLS)-containing microalgae with emphasis on algaenan occurrence.

The neutral lipid profiles of nine species of thin trilaminar outer wall (TLS)-containing freshwater and marine microalgae from the class of Chlorophyceae were studied with emphasis on the relationship between the lipid content and the occurrence of insoluble non-hydrolysable biopolymer (i.e. algaenan). All the freshwater microalgae produce a highly aliphatic algaenan. In sharp contrast, no algaenan was isolated from the two marine microalgae, Chlorella marina and Chlorella minutissima marina, supporting the absence of a close relationship between the presence of TLS and the occurrence of algaenan. High molecular weight straight-chain hydrocarbons (C23-C29) were identified in most of the algaenan-producing microalgae and in the algaenan-devoid C. minutissima marina, whereas only low molecular weight hydrocarbons were detected in algaenan-producing Scenedesmus subspicatus and in algaenan-devoid C. marina. Sterols, phytol and fatty alcohols were the major constituents of the polar fraction of the neutral lipids of all the microalgae investigated. High molecular weight saturated or mono-unsaturated alcohols were detected in C. emersonii and in all the microalgae belonging to the genus Scenedesmus. High amounts of saturated C30 and C32 alpha,omega-diols were also detected in S. subspicatus, S. armatus and S. pannonicus. Three classes of lipids were encountered in very small amounts in the medium polarity fraction of the neutral lipids of the microalgae investigated: (i) Monoesters composed predominantly of saturated C16 or C18 fatty acids and saturated C8, C16 or C18 alcohols and (ii) long-chain methyl ketones from C25 to C31 were detected in several species and (iii) methyl esters of fatty acids ranging from C16 to C28 were identified in all the microalgae. Attempts to use the neutral lipid composition and particularly the unusual long-chain lipids, as specific indicators of the occurrence of algaenan in TLS-containing microalgae were unsuccessful.

Artifactual origin of mycobacterial bacteran. Formation of melanoidin-like artifact macromolecular material during the usual isolation process

Abstract Three species of mycobateria are shown to afford quite a high level of insoluble, non-hydrolysable (INH) material when subjected to usual drastic saponification and acid hydrolysis. The spectroscopic features (FTIR, solid-state 13C NMR), the thermal behaviour (DTG analysis) and the chemical degradation products (alkaline KMnO4 oxidation) of these materials are compared with those of melanoidin-like polymers synthesized from a mixture of monosaccharides and amino acids occurring in the mycobacterial cell walls. The mycobacterial INH materials, thus, appear to correspond to artifacts generated during the isolation process. The implication of these results, on the contribution of such melanoidin-like artifact macromolecular materials in the INH residues previously isolated from other microorganisms is discussed. A new process of isolation avoiding the formation of such artifacts is proposed.

An improved method for the isolation of artifact-free algaenans from microalgae

Abstract A new process for the isolation of algaenans (insoluble non-hydrolysable, highly aliphatic biopolymers of microalga cell walls) which avoids their contamination with melanoidin-like polymer artifacts is presented and the algaenans of two species from the Chlorophyceae (Scenedesmus communis and Botryococcus braunii) are re-examined. Preliminary release of the polysaccharides from these microorganisms by trifluoroacetic acid hydrolysis affords a pure, or much less contaminated, algaenan for the two species. Re-examination of the pyrolysate of S. communis algaenan indicates that the long-chain n-alkylnitriles, previously detected when the algaenan was isolated by the usual process ( Berkaloff et al., 1983 ), do not actually originate from this biopolymer. We suggest that some nitrogen-containing molecules present in S. communis (or in other Chlorophyceae species) are incorporated into the structure of the melanoidin-like polymers generated when the algaenan is isolated by the usual process which lead, upon pyrolysis, to nitriles. Consideration of previous data, on the pyrolysates of numerous kerogens, suggests that a similar process occurs under natural conditions during early diagenesis.

Occurrence of high molecular weight lipids (C80+) in the trilaminar outer cell walls of some freshwater microalgae. A reappraisal of algaenan structure

Abstract The purified cell walls of mother cells (CWM) were isolated from three strains of trilaminar sheath (TLS)- and algaenan-containing freshwater microalgae Chlorella emersonii, Tetraedron minimum and Scenedesmus communis. The chemical structures of CWM and algaenans were investigated by means of tetramethylammonium hydroxide (TMAH) hydrolysis and tetramethylammonium hydroxide thermochemolysis. The compounds released were characterised by 1H and 13C-NMR, gel permeation chromatography and desorption chemical ionisation mass spectrometry. The results show that the outer cell walls of the microalgae are constituted, at least in part, of linear (poly)esters containing extremely long chain alcohol and acid moieties (up to C80) and that algaenans are mainly composed of extremely long chain (di)carboxylic acids up to C120. The present results which are in direct contrast to the previous three-dimensional architecture proposed for algaenans, led us to re-interpret the algaenan structure.

Carbohydrate composition and characterization of sugars from the green microalga Botryococcus Braunii

The amount of the extracellular polysaccharides released in the culture medium by five strains of Botryococcus braunii ranges from 250 mg to 1 g/l. These extracellular polysaccharides are heterogeneous polymers of high Mr. In all the strains galactose is the main component of the polysaccharides. Besides this, fucose, rhamnose, glucose and two unusual sugars are also present in significant amount in the extracellular polysaccharides of some of the strains examined. The latter were identified by GC and GC-MS analyses as 3-O-methyl fucose and 3-O-methyl rhamnose.

High molecular weight lipids from the trilaminar outer wall (TLS)-containing microalgae Chlorella emersonii, Scenedesmus communis and Tetraedron minimum

High molecular weight lipids were isolated from Chlorella emersonii, Scenedesmus communis and Tetraedron minimum, thin trilaminar outer wall (TLS)-containing freshwater microalgae producing an insoluble non-hydrolysable biopolymer (i.e. algaenan). Molecular weight determination by gel permeation chromatography indicated that their molecular weights range from ca. 400 to 2000 Da. Flash pyrolysis with in situ methylation using tetramethylammonium hydroxide (TMAH) and alkaline hydrolysis showed that the high molecular weight lipids isolated from C. emersonii and S. communis are mainly composed of saturated n-C26 and n-C28 fatty acids and alcohols and of saturated n-C30 and n-C32 alpha,omega-diols and omega-hydroxy acids. In contrast the high molecular weight lipids isolated from T. minimum are predominantly composed of long-chain fatty acids and omega-hydroxy acids. Aromatic moieties were also identified in small amounts in the thermochemolysate and in the hydrolysate. Chemical structural models containing long-chain mono- and polyesters were proposed for the high molecular weight lipids isolated from the three microalgae in agreement with analytical and spectroscopic data. Structural similarity between the outer cell wall of these microalgae and the cuticular membrane of higher plants is suggested.

Influence of growth status on composition of extracellular polysaccharides from two chlamydomonas species

The extracellular polysaccharides released by Chlamydomonas augustae at the beginning of growth contain mainly arabinose, glucose and galactose. Methylation analysis revealed that the major fraction of these extracellular polysaccharides can be described as a highly branched polymer composed of (1, 3, 4)-linked glucose and terminal arabinose and galactose units. The chemical composition of these extracellular polysaccharides varies during growth and in the stationary phase of growth glucose and glucuronic acid are the main components. The major fraction of the extracellular polysaccharides can be then described as a linear polymer composed of (1, 4)-linked glucose and (1, 4)-linked glucuronic acid. In sharp contrast, the extracellular polysaccharides from C. corrosa are independent of growth status and contain arabinose and galactose as major sugars. Methylation analysis indicated a highly branched polysaccharide composed of arabinose as unique branch point units and of terminal galactose residues.

Influence of food web structure on the biochemical composition of seston, zooplankton and recently deposited sediment in experimental freshwater mesocosms

The effects of food web structure on the quantity and biochemical composition of seston, zooplankton and recently deposited sediment in experimental freshwater mesocosms were examined. Food web structure was manipulated by addition of zooplanktivorous fish. Biochemical characterisations were carried out using lipid biomarkers (sterols, fatty acids, chlorophyll-derived compounds and long-chain alkanediols). Fish addition decreased zooplankton biomass and increased seston biomass and deposited sediment through a trophic cascade. Fish presence strongly influenced the biochemical characteristics of seston and sediment. In contrast, food web structure had a minor impact on the lipid biomarker composition of zooplankton. Although the relative abundance of sterols in the different compartments did not differ strongly between treatments, sterol profiles in seston and sediment depended on food web structure. The predominance of Δ7-sterols in seston and sediment in the fish treatment indicated a major contribution of Chlorophyceae. In contrast, the distribution of sterols in seston and sediment in the fishless treatment, dominated by cholesterol, indicated a major zooplanktonic input. The distribution of fatty acids and the relative abundance of chlorophyll-derived compounds and long-chain alkanediols agreed with the predominant contribution of phytoplankton or zooplankton to seston and sediment in the two treatments. The relative abundance of bacterial biomarkers suggested that the contribution of bacteria was rather low. The high relative abundance of polyunsaturated fatty acids (PUFAs) and the absence of stanols in sediments suggested low microbial reworking of organic matter in the recently accumulated sediments. The trophic cascade, generated by the addition of fish, increased the relative abundance of PUFAs in deposited organic matter, thus enhancing sediment quality and potential degradability.