Fate of dietary sucrose and neosynthesis of amino acids in the pea aphid, acyrthosiphon pisum, reared on different diets

The fate of sucrose, the major nutrient of an aphid's natural food, was explored by radiolabeling in the pea aphid Acyrthosiphon pisum. To investigate the influence of nitrogen quality of food on amino acid neosynthesis, pea aphids were reared on two artificial diets differing in their amino acid composition. The first (diet A) had an equilibrated amino acid balance, similar to that derived from analysis of aphid carcass, and the other (diet B) had an unbalanced amino acid composition similar to that of legume phloem sap. Aphids grown on either diet expired the same quantity of sucrose carbon as CO(2), amounting to 25-30 % of the ingested sucrose catabolized in oxidation pathways. On diet A, the aphids excreted through honeydew about twice as much sucrose carbon as on diet B (amounting to 12.6 % of the ingested sucrose for diet A and 8.4 % for diet B), while amounts of sucrose carbons incorporated into exuviae were almost identical (1.9 % of the ingested sucrose on diet A and 2.7 % on diet B). There was also no difference in the amounts of sucrose carbon incorporated into the aphid tissues, which represented close to 50 % of the ingested sucrose. Sucrose carbons in the aphid tissues were mainly incorporated into lipids and the quantities involved were the same in aphids reared on either diet. On diet B, we observed neosynthesis of all protein amino acids from sucrose carbons and, for the first time in an aphid, we directly demonstrated the synthesis of the essential amino acids leucine, valine and phenylalanine. Amino acid neosynthesis from sucrose was significantly higher on diet B (11.5 % of ingested sucrose carbons) than on diet A (5.4 %). On diet A, neosynthesis of most of the amino acids was significantly diminished, and synthesis of two of them (histidine and arginine) was completely suppressed. The origin of amino acids egested through honeydew was determined from the specific activity of the free amino acid pool in the aphid. Aphids are able to adjust to variation in dietary amino acids by independent egestion of each amino acid. While more than 80 % of excreted nitrogen was from food amino acids, different amino acids were excreted in honeydew of aphids reared on the two diets. The conversion yields of dietary sucrose into aphid amino acids determined in this study were combined with those obtained previously by studying the fate of amino acids in pea aphids reared on diet A. The origin of all the amino acid carbons in aphid tissues was thus computed, and the metabolic abilities of aphid are discussed from an adaptive point of view, with respect to their symbiotic status.

Molecular characterization of the principal symbiotic bacteria of the weevil Sitophilus oryzae: a peculiar G + C content of an endocytobiotic DNA.

The principal intracellular symbiotic bacteria of the cereal weevil Sitophilus oryzae were characterized using the sequence of the 16S rDNA gene (rrs gene) and G + C content analysis. Polymerase chain reaction amplification with universal eubacterial primers of the rrs gene showed a single expected sequence of 1,501 bp. Comparison of this sequence with the available database sequences placed the intracellular bacteria of S. oryzae as members of the Enterobacteriaceae family, closely related to the free-living bacteria, Erwinia herbicola and Escherichia coli, and the endocytobiotic bacteria of the tsetse fly and aphids. Moreover, by high-performance liquid chromatography, we measured the genomic G + C content of the S. oryzae principal endocytobiotes (SOPE) as 54%, while the known genomic G + C content of most intracellular bacteria is about 39.5%. Furthermore, based on the third codon position G + C content and the rrs gene G + C content, we demonstrated that most intracellular bacteria except SOPE are A + T biased irrespective of their phylogenetic position. Finally, using the hsp60 gene sequence, the codon usage of SOPE was compared with that of two phylogenetically closely related bacteria: E. coli, a free-living bacterium, and Buchnera aphidicola, the intracellular symbiotic bacteria of aphids. Taken together, these results show a peculiar and distinctly different DNA composition of SOPE with respect to the other obligate intracellular bacteria, and, combined with biological and biochemical data, they elucidate the evolution of symbiosis in S. oryzae.

The effect of cold acclimation and deacclimation on cold tolerance, trehalose and free amino acid levels in Sitophilus granarius and Cryptolestes ferrugineus (Coleoptera).

Canadian and French laboratory strains of Sitophilus granarius (L.) and Cryptolestes ferrugineus (Stephens) were cold acclimated by placing adults at 15, 10 and 5 degrees C successively for 2wk at each temperature before deacclimating them for 1wk at 30 degrees C. Unacclimated S. granarius had an LT(50) (lethal time for 50% of the population) of 12days at 0 degrees C compared with 40days after the full cold acclimation. At -10 degrees C, unacclimated C. ferrugineus had an LT(50) of 1.4days compared with 24days after the full acclimation. Cold acclimation was lost within a week after returning insects to 30 degrees C. Trehalose, as well as the amino acids proline, asparagine, glutamic acid and lysine were higher in cold acclimated insects for both species. For S. granarius, glutamine was higher in cold acclimated insects and isoleucine, ethanolamine and phosphoethanolamine, a precursor of phospholipids, were lower in cold acclimated insects. For C. ferrugineus, alanine, aspartic acid, threonine, valine, isoleucine, leucine, phenylalanine and phosphoethanolamine were higher in cold acclimated insects. For both species tyrosine was lower in cold acclimated insects. There were small but significant differences between Canadian and French strains of S. granarius, with the Canadian strain being more cold hardy and having higher levels of trehalose. There were small but significant differences between male and female S. granarius, with males being more cold hardy and having higher levels of proline, asparagine and glutamic acid. In conclusion, high levels of trehalose and proline were correlated with cold tolerance, as seen in several other insects. However, correlation does not prove that these compounds are responsible for cold tolerance, and we outline further tests that could demonstrate a causal relationship between trehalose and proline and cold tolerance.

Biogenesis and metabolic fate of docosahexaenoic and arachidonic acids in rat uterine stromal cells in culture.

To gain some insight into the mechanisms involved in the opposing effects of arachidonic acid and docosahexaenoic acid on the growth of rat uterine stromal cells (UIII cells), the dynamics of the uptake, conversion, and incorporation of labeled 18:2(n-6), 18:3(n-3), 20:4(n-6), 20:5(n-3), and 22:6(n-3) into lipid pools and phospholipid subclasses were examined. A very active and time-dependent conversion of [14C]18:3(n-3) to higher homologs was observed; 64.7 +/- 0.7 and 11.5 +/- 0.4% of the [14C] radioactivity incorporated in cellular lipids was recovered as 22:5(n-3) and 22:6(n-3) after 72 h incubation, respectively. The distribution of labeled fatty acids obtained after 72 h incubation with [3H]20:5(n-3) was not significantly different from that observed with 18:3(n-3). Arachidonic acid was the major fatty acid formed from [14C]18:2(n-6) and only trace amounts of 22:5(n-6) were detected. When cells were incubated for 72 h with 20:4(n-6), more than 75% of the radioactivity was recovered as arachidonate and slightly higher amounts of 22:4(n-6) and 22:5(n-6) were formed compared to those obtained after incubation with 18:2(n-6). Using both [14C]- and [3H]22:6(n-3), no significant retroconversion of labeled 22:6(n-3) occurred in the cells. More than 90% of labeled 20:4(n-6) and 22:6(n-3) taken up by the cells were esterified into phospholipids, but significant differences in their distribution among phospholipid classes and subclasses were observed. Docosahexaenoic acid was more rapidly and efficiently incorporated into phosphatidylethanolamine than 20:4(n-6) and was principally recovered in plasmalogens. Arachidonic acid was mainly incorporated in the diacyl subclasses of phosphatidylcholine and phosphatidylethanolamine and in phosphatidylinositol. The divergent profiles of these two fatty acids within the phospholipid compartments provide some information for the mechanisms of their opposite effects on UIII cell growth.

Fourier processing of liquid chromatograms using flow radioactive detection.

Flow radioactivity counters coupled to liquid chromatography devices cause a systematic bias to the separation by broadening peaks within the radiochromatogram. Such signal smearing may be evaluated on standardization runs with a single peak, using the ratio between Fourier transforms of whole chromatographic data for the measured radioactivity time series (radioactivity channel) and for the concentration time series (optical density channel). This ratio constitutes a kernel suitable to perform the deconvolution of any radiochromatogram performed under similar conditions. Through deconvolution, the signal smearing is removed, reverting to peaks with the same geometry as in the concentration chromatogram: same retention time, peak width, and shape. The deconvolution method in processing radiochromatograms allows an easier interpretation and gives more reliable radioactivity quantification (improved linearity of the measured response). Fourier transformation of the radiochromatogram also allows the removal of transitory events (noise) through the correlation procedure. This method may provide substantial gain in sensitivity, depending upon the residence time of the sample in the counting cell.

Study of relationship of ABO and Rh blood group, and HLA antigens with parasitic diseases.

A study has been performed on 467 cases of differents parasitic diseases and ABO blood groups. With classical statistical methods, we did not find any correlation, but with a large number of variables, we used the factorial analysis, and we obtained maps with relationship O-hookworm and strongloidiasis. A-giardiasis, B-Entamoeba coli. But AB group seems to be far from all parasitosis. Besides, blood group and severity of diseases seem not to be related. With HLA groups, a study by microlymphocytotoxicity on 36 West-African (Sarakole people) showed that HLA B5 is predominant in cases of schistosomiasis.

[Dynamics of egg maturation in the parasitoid Lixophaga diatraeae (Diptera, Tachinidae) raised in a substitute host, Galleria mellonella (Lepidoptera, Pyralidae)]. / Dynamique de la maturation des oeufs chez le parasitoïde Lixophaga diatraeae (Diptera, Tachinidae) élevé dans un hôte de substitution Alleria mellonella (Lepidoptera, Pyralidae).

The content of the uterus and ovaries of L. diatraeae (an ovolarviparous tachinid fly) was studied by dissecting 121 females 0 to 25 days old. Several size classes of flies (p: small; m: medium; g: big) were used, weighing 10 to 12.5 mg, 12.5 to 13.5 mg, and 13.5 to 16 mg, respectively. The mean number of ovarioles per ovary, correlated to female size, was 12.1 for p as against 12.9 for m + g females. The total mean number of eggs and oocytes changed with female age and weight. For 0, 5, 10 and 15-day old females, this number was 56, 149, 158 and 202, respectively in g flies and 51, 128, 141 and 139, respectively, in p ones. To study egg maturation dynamics, we counted the total number of eggs + oocytes per p female (Y1), the eggs in the uterus (Y2), partially embryonated eggs (Y3), and entirely embryonated eggs (Y4). The experimental results were fitted to various age functions using a non-linear adjustment program. The models fitting each datum best were asymptotic functions of the form, Y = A [1-e-K(x-D)], where A is the asymptotic value, K a speed constant of the studied phenomenon and D age at the beginning of the phenomenon. At emergence time, each female contained a mean of 50 oocytes which passed into the uterus immediately after mating. Egg production continued for at least 10 days after emergence. The rate of embryogenesis seemed to be influenced by the number of eggs in the uterus and/or the age of the fly; it was high for the first eggs then decreased progressively. In our conditions, the first eggs with a planidium ready to hatch appeared at 10 days post-emergence. To obtain a maximum number of larvae in good health, it is better to dissect 12 to 18-day old females. The egg volume increases slightly during embryogenesis.