Heavy metals and PAH assessment based on mussel caging in the north coast of Tunisia [Mediterranean Sea]

In the framework of the Mytilos project [Interreg IIIB Medocc], international research cruises were carried out in 2006 in order to evaluate the level of Heavy metals and polycyclic aromatic hydrocarbons [PAH] along the coast of the western basin of the Mediterranean Sea. Caged mussels [Mytilus galloprovincialis] were placed in situ at six sites in the North coast of Tunisia, Results showed total PAH levels were in the range 45.6-241.6 ng/g dry weight [dw]. The ranges of trace metals concentrations expressed in ug/gdw are: Hg [0.1-0.2], Pb [0.4-0.7], Cd [0.9-2.9], Cu [2.9-3.9], Fe [117-248] and Zn [250-426]. Higher concentrations were observed at Rades, La Galite and Tabarka which can be attributed to the industrial activities implanted in the coast of Algeria and in the city of Rades. Concentrations of PAH, Cd, Pb, Fe and Zn are generally different from initial concentrations [before caging], depending on the adaptability of transplanted mussels to be used as bio-indicator of contaminants. Yet bio-monitoring using mussels give information on compound bioavailability which depends on their ability to accumulate contaminants in its tissue

Solution structure and antibacterial mechanism of two synthetic antimicrobial peptides / 生物工程学报

Mytilin-derived-peptide-1 (MDP-1) and mytilin-derived-peptide-2 (MDP-2) are two truncated decapeptides with reversed sequence synthesized corresponding to the residues 20-29 of mytilin-1 (GenBank Accession No. FJ973154) from M. coruscus. The objective of this study is to characterize the structural basis of these two peptides for their antimicrobial activities and functional differences, and to investigate the inhibitory mechanism of MDPs on Escherichia coli and Sarcina lutea. The structures of MDP-1 and MDP-2 in solution were determined by 1H 2D NMR methods; the antibactericidal effects of MDPs on E. coli and S. lutea were observed by transmitted electron microscopy (TEM). Both MDP-1 and MDP-2 have a well-defined loop structure stabilized by two additional disulfide bridges, which resemble the-hairpin structure of mytilin-1 model. The surface profile of MDPs' structures was characterized by protruding charged residues surrounded by hydrophobic residues. TEM analysis showed that MDPs destroyed cytoplasmic membrane and cell wall of bacteria and the interface between the cell wall and membrane was blurred. Furthermore, some holes were observed in treated bacteria, which resulted in cell death. Structural comparison between MDP-1 and MDP-2 shows that the distribution of positively charged amino acids on the loop of MDPs is topologically different significantly, which might be the reason why MDP-2 has higher activity than MDP-1. Furthermore, TEM results suggested that the bactericidal mechanisms of MDPs against E. coli and S. lutea were similar. Both MDP-1 and MDP-2 could attach to the negatively charged bacterial wall by positively charged amino acid residues and destroy the bacteria membrane in a pore-forming manner, thus cause the contents of the cells to release and eventually cell death.

Designation, solid-phase synthesis and antimicrobial activity of Mytilin derived peptides based on Mytilin-1 from Mytilus coruscus / 生物工程学报

As a key role in mussel defense system, Mytilin is an important antibacterial peptide isolated from the mussel serum. The structural and functional researches on Mytilin showed that the fragment connecting two beta-sheets in a stable beta-hairpin structure was probably required for antimicrobial activity. To elucidate the structural features and the antimicrobial activity of this fragment, we re-designed and synthesized two peptides corresponding to the main mimic structures of Mytilin-1 from Mytilus coruscus, we named these two peptides Mytilin Derived Peptide-1 and Mytilin Derived Peptide-2, respectively. Using a liquid growth inhibition assay, we evaluated their activity towards Gram-positive, Gram-negative bacteria and fungus. The results showed that both peptides can inhibit the growth of Gram-positive, Gram-negative bacteria and fungus. Besides, these two peptides showed high stability in heat water and human serum. These works laid the foundation for further research on the molecular mechanism of Mytilin and for further exploitation of antibacterial peptides with lower molecular mass and more stable structure.

Allozymic variation and differentiation in the chilean blue mussel, Mytilus chilensis, along its natural distribution

Genetic differentiation in the Chilean blue mussel Mytilus chilensis (Hupé 1854) was investigated based on the variation in the allozyme frequencies of Pgm, Gpi, Icd, Me, Gsr, Lap and Pep in eight samples collected along 1800 km from Arauco (VIII Region) to Punta Arenas (XII Region). Despite the large geographic separations, values of Neis unbiased genetic distance, D (0.004-0.048) and standardised genetic variation among populations, Fst (0.011-0.055) were small. The levels of gene flow (Nm = 8) found in this study prevent the effect of differentiation among populations by genetic drift. This findings indicate that its long-lived planktotrophic larvae provides this species with considerable dispersal ability throughout its range which is favoured by the ocean currents along the chilean coast. In terms of management of the M. chilensis fishery, the results provide no evidence for discrete stocks, with the possible exception of the Punta Arenas population. Considering the intensive aquaculture activities with this species the present study provide preliminary data which can be used as a baseline for further characterization and /or monitoring these mussel populations.

Biochemical Characteristics of Vibrios isolated from Cultured Shellfish, Ruditapes philippinarum, and Some Species of Wild Shellfish

This study was conducted to investigate the vibrio flora in edible shellfish (Ruditapes philippinarum, Scapharca broughtonii, Batillus cornutus and Mytilus coruscus) which were purchased from seafood-market or collected from shellfish culture bed in Pusan and Masan Bay from May to October 1997. Sixty-three vibrio strains were identified among 438 collected strains. Five species of vibrios [V. alginolyticus (22 strains), V. parahaemolyticus (35 strains), V. costicola (2 strains), L. damsela (V. damsela 2 strains), and V. cholerae non-Ol (2 strains)] were identified by their phenotyfic and biochemical characteristics. Four groups (142 strains) were identified as genus Vibrio by their biological characteristics, but they could not be identified to the species level.