Charles Jeuniaux

Chitin biomass and production in the marine environment

Abstract The total production of chitin has been tentatively calculated on the basis of original analytical data on chitin in zooplankton and in benthic communities growing on experimental substrates studied in the Mediterranean Sea, together with data in the literature dealing with total and exuviae production by krill and by some large crustacean species. It appears that crustaceans are the main chitin producers both in planktonic and benthic ecosystems, and that mean total production of chitin in the whole marine biocycle is at least of 2.3 million metric tons per year.

Chitin biodegradation in marine environments: An experimental approach

Abstract Chitin biomasses and production in marine environments are quite high. Planktonic biocenoses are the main producers and one should expect that sediments, mainlyorganoclastic ones, will constitute some kind of reserve compartment for the biogeochemical cycle of this polymer. In fact, this is not the case. The low chitin biomass in most marine sediments can only be explained if chitin is weathered at the same rate as it is produced. In order to test this hypothesis, we developed an experimental approach to chitin biodegradation in marine environments. In open water conditions, zooplanktonic remains are first degraded by autolytic processes making most organic compounds readily susceptible for further hydrolysis by extrinsic decomposers. Different populations (with high densities and various hydrolytic potentials) follow each other. The sequence of hydrolytic activities optimizes the recycling of most dietritic compounds including nearly 90% of the chitin produced. At sediment-water interface, the remaining material appears to be pulverized and incorporated into the aerobic sedimentary layers while the decomposer community changes once again. Sediment chitinoclasts are opportunistic and densities react quickly to chitin input. In sediments, oxic and anoxic, chitin appears essentially present in the form of chitinoproteic matrices inside mineralized skeletons. A rich population of microborers develops on these matrices by secreting extracellular hydrolases. Densities of microborers of 250–450×10 3 cm t2 are currently encountered. Anaerobic decomposers are more adapted to refractory compounds than aerobic ones. This leads to a nearly complete mineralization of the chitinoproteic matrices embedded in the biotic sedimentary layers (more than 90% of the chitin weathered within less than two years).

Stable isotopic composition of chitin from arthropods recovered in archaeological contexts as palaeoenvironmental indicators

Abstract The effects of biodegradation and heating on the stable carbon, nitrogen, hydrogen and oxygen isotope ratios of chitin in arthropods were studied. Chitinous exoskeletons from seven aquatic arthropod species were subjected to anaerobic marine biodegradation in mud, to terrestrial biodegradation in soils, and to thermal degradation under anaerobic and aerobic conditions. The isotope ratios of chromatographically separated D-glucosamine hydrochloride and derivatives from treated and untreated specimens were then compared. Carbon, nitrogen, oxygen and hydrogen stable isotope ratios were all found to be conserved during partial degradation of chitin. Micromorphological comparative studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that no fungal chitin or other contaminants were present in the chitins that were chemically isolated from biodegraded substrates. Our results indicate that it will be possible to use stable isotope ratios of archaeological chitin samples for environmental and climatic reconstructions. An illustration of the utility of this approach comes from the observation that the stable isotope ratios of chitin from crustacean exoskeletons recovered from archaeological sites with ages up to 1400 years bp are in good agreement with measurements on modern crustaceans from similar environments.

Systematic characters of some polychaetes (Annelida) at the level of the chemical composition of the jaws

Abstract The mandibles and maxillae of the buccal ventral organ of 2 species of Eunicidae ( Marphysa sanguinea and Eunice torquata ) are highly calcified, in contrast to the jaws of 4 species of other families of ‘errant’ predacious Polychaetes (Nereidae, Nephthyidae, Aphroditidae and Glyceridae) with axial proboscis. The amino acid composition of the structural proteins of these buccal pieces is also different in the two groups. The structural proteins of the jaws of Glycera convoluta (Glyceridae) are essentially made up of glycine and histidine (up to 86 residues per 100 residues). These chemical characters confirm the phyletic relationships proposed by Dales. 1

Recherches sur les chitinases II. — Purification de la chitinase d'un streptomycète, et séparation électrophorétique de principes chitinolytiques distincts

AbstractThe purification and concentration of the exochitinase of a streplomycete are described. The procedure consists essentially of a mass adsorption on colloidal chitin, followed by washing out and enzymie hydrolysis of the adsorbant, and of two consecutive fractionnations by ammonium sulfate. The chifinolyfic activity has been concentrated 70 times, with a yield of 27 %.The purified solution is homogeneous in the ultracentrifuge (molecular weight 30 000) and also during the tests of solubility in ethanol or ammonium sulfate solutions.By electrophoresis at pH 8.2 in agar-agar plates, it has been possible to isolate three different chitinases, besides a small fraction of a non-chitinolytic protein (1.5 %). These three chitinases show slightly different electrophoretic patterns; they have however the same specific activities, but, when they are recombined, a synergistic effect on chitin hydrolysis is observed.

Chitinolytic enzymes of the gastric mucosa of perodicticus potto (primate prosimian): Purification and enzyme specificity

Abstract 1. 1. Enzymatic extracts of Perodicticus potto gastric mucosa showed chitinolytic activity together with lysozymic activity. 2. 2. After purification by adsorption on colloidal chitin and gel chromatography, an enzymatic preparation with high chitinolytic activity was devoid of any lysozymic activity. 3. 3. The gastric chitinolytic enzymes of Perodicticus potto are thus ‘true’ chitinases specific of the β -1,4- N -acetylglucosamine linkages in chitin molecule.

Chitin preservation in Quaternary Coleoptera: preliminary results

Abstract Although many fossil organisms are known to have had chitinous exoskeletons, there is conflicting information concerning chitin preservation in fossils. Remains of arthropods, particularly insects, are relatively common in Cenozoic deposits and provide useful paleoenvironmental information. Experimental studies on the chemistry of modern and fossil arthropod chitin suggest that it may remain sufficiently stable for paleoecologic and paleoclimatic information to be derived from stable isotope analysis. Such techniques might be applied to a wide range of chitinous fossils. Analyses of Quaternary Coleoptera from late-glacial and last interglacial deposits indicate that chitin comprises 10–30% of the dry weight of fossil beetle fragments. These amounts represent half to three-quarters of the amount of chitin reported for a range of modern insects (25–40%). The abundance and quality of chitin preservation has important implications for paleoentomological research.

Contributions à la biochimie du ver à soie. XXVII. Tréhalose, tréhalase et mue

AbstractDuring the development of the Silkworm, the amount of blood trehalose sharply decreases at each moult, and also during the fasting period corresponding to spinning. the fall of blood trehalose concentration during the moults is related to the release of the inhibition of the trehalase present in the hemolymph.The presence of a trehalase in the muscles and in the digestive tract is confirmed. This enzyme has not been detected in the fat body, in the epidermis or in the silkglands.In the fat body, there exists an inverse relationship between glycogen and trehalose, the former disappearing almost completely at each moult, whereas the amount of trehalose tends to remain at a nearly constant level. On the other hand, the bulk of the fat body is consumed to a large extent during the periods of chitin synthesis.The gluconeogenesis during the silkworm development and the metabolism of chitin synthesis at each moult, are discussed in the light of these experimental data.

Structure, synthèse et dégradation des chitinoprotéines de la cuticule des Crustacés décapodes

Abstract Structure, synthesis and degradation of the chitinoproteins of decapod crustaceans The procuticle of the Crustacea Decapoda is formed of stacked laminae composed of fibre beds in which the fibres run parallel to the surface and undergo a slight and progressive change in orientation from one bed to another. The basic structural unit of the procuticle is a microfibril made up of a core of chitin criystallite surrounded by a protein sheath. Microfibrils arise at the surface of plasmamembrane plaques which are concerned with their deposition and orientation. According to the degree of mineralization, microfibrils are either homogeneously distributed (membranous layer) or secondarily associated into reticulate structures (pigment‐ed layer) or into macrofibres (principal layer). In the newly secreted procuticular sheets the chitin‐proteic fibres are disposed around long vertical microvilli originating from the epidermis. The plasma‐membrane of the microvilli appears to be closely concerned with the dep...

Chitinous cuticle and systematic position of tardigrada

Abstract The chitinous nature of the cuticle, jaws and stomodaeum of three species of Tardigrada has been definitely proven using a specific micromethod involving a preparation of purified chitinase. These chemical characteristics are in favour of the phylogenetic closeness between Tardigrada and the Arthropoda.