Genetic differences between Tunisian camel and sheep strains of the cestode Echinococcus granulosus revealed by SSCP

Ovine and dromedary Echinococcus granulosus isolates from Tunisia were identified as G1 and G6 strains based on polymorphism of the mitochondrial cytochrome C oxydase CO1. Single strand conformation polymorphism (SSCP) was used in order to examine the genetic variation within and between Tunisian G1 and G6 strains and to estimate the extent of selfing. The dromedary isolates are genetically distinct from sheep isolates (high value of genetic variation between populations: Fst= 0.46). No significant deficiency in heterozygotes was found in sheep isolates, whereas heterozygote deficiency (suggesting selfing) was found in a limited number of camel isolates.     

Survival strategies of pomegranate and almond trees in a fluoride polluted area

In the southern suburb of Sfax (Tunisia), almond and pomegranate trees grow in the vicinity of a phosphate fertilizer-producing factory. In order to reveal strategies adopted by these fruit species to live in restrictive conditions, we investigated the effect of fluoride pollution on the distribution of some elements during the growing season. The results show that calcium and magnesium play an important role in trapping fluoride and delaying the appearance of necroses. Sensitive fruit species, like the almond tree, tend to reduce (F-) toxicity by increasing leaf Mg content, following a decrease in leaf calcium. Since the Mg has multiple roles in the plant metabolism, the MgF affinity seems to be temporary and constitutes, in the long run, a limiting factor for the main physiological processes. Therefore, it appears that resistant species, like pomegranate, have the ability, during fluoride intoxication, not only to assimilate calcium ions but also to maintain Mg concentrations at an adequate level, thus ensuring the cell smooth running. When calcium is no more available, Mg is taken from the chlorophyll molecule as MgF2, and so damage may appear as marginal necroses. By comparing fluoride content of necrotic and healthy leaf slices, it appears that marginal necroses represent typical symptoms of fluoride pollution. By increasing their phosphorus concentration, sensitive fruit species tend to reduce damage intensity, whereas resistant ones tend to avoid F- toxicity.     

Under low irradiation,the light regime modifies growth and metabolite production in various species of microalgae

The effects of continuous light exposure (24L:0D) and a 12 h:12 h light/dark regime (12L:12D) were compared on the growth and carotenoid, protein, sugar, lipid, and fatty acid contents in Chlorella vulgaris, Nannochloropsis sp., Isochrysis galbana, and Dunaliella salina cultured in a batchwise facility. These microalgae were grown axenically under a low photon flux density (PFD) of 27 μmol photons m^?2 s^?1. C. vulgaris, Nannochloropsis sp., and I. galbana exhibited the highest cell densities when cultured under 24L:0D, whereas D. salina grew better under the alternating light/dark regime. I. galbana accumulated high levels of proteins, sugars, and lipids and exhibited the highest carotenoid content under 24L:0D. Protein production was enhanced in C. vulgaris under 24L:0D. The highest total lipid content was recorded for D. salina, reaching 74.6 % of total proteins, sugars, and lipids in cells at the stationary phase when grown under 12L:12D. The light/dark regime at low PFD was sufficient to stimulate the accumulation of monounsaturated and polyunsaturated fatty acids in all four algae. Their levels, like those of saturated fatty acids, did not differ significantly under the two light regimes. D. salina was an important source of tetradecenoic acid 14:1(n-5). Nannochloropsis sp. produced a large amount of the essential eicosapentaenoic acid, which reached 20 % of total fatty acids under 12L:12D, while I. galbana exhibited the highest level of docosahexaenoic acid, which reached 21 % under both light regimes. This study demonstrated the feasibility of culturing microalgae under low PFD in order to produce large quantities of valuable metabolites, especially various lipids with neutraceutical value.     

Complete genome sequence of the fish pathogen Flavobacterium psychrophilum

We report here the complete genome sequence of the virulent strain JIP02/86 (ATCC 49511) of Flavobacterium psychrophilum, a widely distributed pathogen of wild and cultured salmonid fish. The genome consists of a 2,861,988-base pair (bp) circular chromosome with 2,432 predicted protein-coding genes. Among these predicted proteins, stress response mediators, gliding motility proteins, adhesins and many putative secreted proteases are probably involved in colonization, invasion and destruction of the host tissues. The genome sequence provides the basis for explaining the relationships of the pathogen to the host and opens new perspectives for the development of more efficient disease control strategies. It also allows for a better understanding of the physiology and evolution of a significant representative of the family Flavobacteriaceae, whose members are associated with an interesting diversity of lifestyles and habitats.     

Development and characterisation of an expressed sequence tags (EST)-derived single nucleotide polymorphisms (SNPs) resource in rainbow trout

ABSTRACT: BACKGROUND: There is considerable interest in developing high-throughput genotyping with singlenucleotide polymorphisms (SNPs) for the identification of genes affecting importantecological or economical traits. SNPs are evenly distributed throughout the genome and arelikely to be functionally relevant. In rainbow trout, in silico screening of EST databasesrepresents an attractive approach for de novo SNP identification. Nevertheless, ESTsequencing errors and assembly of EST paralogous sequences can lead to the identification offalse positive SNPs which renders the reliability of EST-derived SNPs relatively low. Furthervalidation of EST-derived SNPs is therefore required. The objective of this work was toassess the quality of and to validate a large number of rainbow trout EST-derived SNPs. RESULTS: A panel of 1,152 EST-derived SNPs was selected from the INRA Sigenae SNP database andwas genotyped in standard and double haploid individuals from several populations using theIllumina GoldenGate BeadXpress assay. High-quality genotyping data were obtained for 958 SNPs representing a genotyping success rate of 83.2 %, out of which, 350 SNPs (36.5 %)were polymorphic in at least one population and were designated as true SNPs. They alsoproved to be a potential tool to investigate genetic diversity of the species, as the set of SNPsuccessfully sorted individuals into three main groups using STRUCTURE software.Functional annotations revealed 28 non-synonymous SNPs, out of which four substitutionswere predicted to affect protein functions. A subset of 223 true SNPs were polymorphic inthe two INRA mapping reference families and were integrated into the INRA microsatellitebasedlinkage map. CONCLUSIONS: Our results represent the first study of EST-derived SNPs validation in rainbow trout, aspecies whose genome sequences is not yet available. We designed several specific filters inorder to improve the genotyping yield. Nevertheless, our selection criteria should be furtherimproved in order to reduce the observed high rate of false positive SNPs which results fromthe occurrence of whole genome duplications.     

Synthesis of trehalose-based compounds and their inhibitory activities against Mycobacterium smegmatis

The synthesis of a library of trehalose-based compounds has been accomplished, and their activities against Mycobacterium smegmatis have been determined. A preliminary structure–activity relationship (SAR) is reported. Despite not having a potent lead, one of the trehalose derivatives displays strong activity when applied with isoniazid (INH), which is known to have low sterilizing activity. The bacteriocidal nature of our compounds against Mycobacterium may be significant for the development of new therapies against tuberculosis.     

Syringopeptin SP25A-mediated killing of gram-positive bacteria and the role of teichoic acid d-alanylation

The Pseudomonas syringae syringopeptins are cationic cyclic lipodepsipeptides that inhibit fungi and bacteria. The homolog syringopeptin (SP)25A was strongly inhibitory to several Gram-positive bacteria with minimum inhibitory concentrations ranging between 1.95 and 7.8 microg mL(-1). In contrast, it was not inhibitory to several Gram-negative bacteria. At 5 and 10 microg mL(-1), SP25A rapidly inhibited the growth of Bacillus subtilis and was bacteriocidal. Teichoic acid D-alanylation dltB- and dltD-defective mutant strains of B. subtilis were more susceptible to SP25A compared with the parental wild-type strain. The degree of susceptibility of the parent strain, but not the dltB and dltD mutant strains, increased at alkaline pH (9.0). In contrast, the parental and mutant strains had the same susceptibilities to syringopeptins SP22A and SP508A at pH 7.0 and 9.0. These results suggest that the cell wall anionic teichoic acids modulate SP25A action against B. subtilis, and they provide an explanation for the selective inhibition of Gram-positive bacteria by SP25A.     

Diversity of Lactic Acid Bacteria Associated with Fish and the Fish Farm Environment, Established by Amplified rRNA Gene Restriction Analysis

Lactic acid bacteria have become a major source of concern for aquaculture in recent decades. In addition to true pathogenic species of worldwide significance, such as Streptococcus iniae and Lactococcus garvieae, several species have been reported to produce occasional fish mortalities in limited geographic areas, and many unidentifiable or ill-defined isolates are regularly isolated from fish or fish products. To clarify the nature and prevalence of different fish-associated bacteria belonging to the lactic acid bacterium group, a collection of 57 isolates of different origins was studied and compared with a set of 22 type strains, using amplified rRNA gene restriction analysis (ARDRA). Twelve distinct clusters were delineated on the basis of ARDRA profiles and were confirmed by sequencing of sodA and 16S rRNA genes. These clusters included the following: Lactococcus raffinolactis, L. garvieae, Lactococcus l., S. iniae, S. dysgalactiae, S. parauberis, S. agalactiae, Carnobacterium spp., the Enterococcus “faecium” group, a heterogeneous Enterococcus-like cluster comprising indiscernible representatives of Vagococcus fluvialis or the recently recognized V. carniphilus, V. salmoninarum, and Aerococcus spp. Interestingly, the L. lactis and L. raffinolactis clusters appeared to include many commensals of fish, so opportunistic infections caused by these species cannot be disregarded. The significance for fish populations and fish food processing of three or four genetic clusters of uncertain or complex definition, namely, Aerococcus and Enterococcus clusters, should be established more accurately.     

MC4R、POU1F1基因对京海黄鸡生长性能的遗传效应

以MC4R和POU1F1基因为候选基因, 采用PCR-SSCP和DNA测序技术检测两个候选基因在京海黄鸡群体中的单核苷酸多态性(SNPs), 同时对候选基因与京海黄鸡生长性能的相关性进行了研究。结果表明, MC4R基因编码区第662 bp位置有G→C碱基的点突变, 在京海黄鸡中检测到AA、AB、BB 3种基因型, A等位基因频率为0.929, B等位基因频率为0.071; 在POU1F1基因exon3在序列的第5 231 bp位置有一个A→T碱基的点突变, 检测到CC、CD、DD 3种基因型, C等位基因频率为0.500, D等位基因频率为0.500。采用GLM模型分析基因型对生长性能的遗传效应, 结果表明, MC4R基因AA基因型个体的4、8、12周龄体重显著地高于BB型个体(P<0.05), 16周龄体重差异极显著(P<0.01); POU1F1基因CD基因型个体体重极显著高于CC型和DD型(P<0.01)。因此推测MC4R和POU1F1基因可能是影响鸡生长性状的主效基因或与主效基因紧密连锁的标记基因, 能够在分子标记辅助选择中用于对鸡生长性状的遗传改良。