Molecular characterization of a novel antimicrobial peptide from Mytilus coruscus.

Antimicrobial peptides (AMPs) are components of the innate immune responses that form the first line of host defense against pathogens. Marine mussels can produce a surprising abundance of cysteine-rich AMPs pertaining to the defensin, myticin, mytilin and mytimycin families, particularly in the circulating hemocytes. In the current study, we purified and characterized a novel cysteine-rich peptide with remarkable antibacterial activity from Mytilus coruscus and designated with myticusin-1, a 104-amino acid long polypeptide including 10 cysteine residues forming an unusual cysteine pattern. Antimicrobial assays demonstrated that myticusin-1 exhibited stronger anti-microbial properties against Gram-positive bacteria more than Gram-negative bacteria and fungus. Furthermore, myticusin-1 caused significant morphological alterations in both Sarcina luteus and Escherichia coli as shown by transmission electron microscopy (TEM). The cDNA of myticusin-1 was cloned and sequenced from the hemocytes cDNA library of M. coruscus. The mRNA transcripts of myticusin-1 are mainly detected in hemocyte, which indicates that myticusin-1 are specifically synthesized and stored in circulating hemocytes. The expression level of myticusin-1 in hemocytes was up-regulated and reached the highest level at 36 h after S. luteus challenge, which was 20-fold increase compared to that of the control group. These results indicated that myticusin-1 was involved in the host immune response against bacterial infection and might contribute to the clearance of invading bacteria.

Influence of pH extremes on sporulation and ultrastructure of Sarcina ventriculi.

Distinct morphological changes in the ultrastructure of Sarcina ventriculi were observed when cells were grown in medium of constant composition at pH extremes of 3.0 and 8.0. Transmission electron microscopy revealed that at low pH (less than or equal to 3.0) the cells formed regular packets and cell division was uniform. When the pH was increased (to greater than or equal to 7.0), the cells became larger and cell division resulted in irregular cells that varied in shape and size. Sporulation occurred at high pH (i.e., greater than or equal to 8.0). The sporulation cycle followed the conventional sequence of development for refractile endospores, with the appearance of a cortex and multiple wall layers. The spores were resistant to oxygen, lysozyme, or heating at 90 degrees C for 15 min. Spores germinated within the pH range of 4.6 to 7.0.

[Electron microscope study of bacteria in dental plaques following the application of fluorides (author's transl)]. / Etude ultrastructurale des bactéries des plaques microbiennes dentaires après applications de fluorures

Gels containing fluorides can have profound effects on dental plaques. These gels contain 2% fluorides in the form of sodium monofluorophosphate and sodium fluoride and are buffered to pH 6.5 when applied to teeth they: - encourage the disappearance of certain bacteria, - inhibit the division of cells and diminish their storage of glycogen, - cause a thickening of the bacterial cell wall, - lead to modifications of the bacterial cell membrane, - precipitate the degeneration of most forms of bacteria, - cause the rapid mineralisation of many bacteria. These widespread effects, and the wholesale degeneration of microbial forms, are a reflection of a major breakdown in bacterial metabolism, and provide a partial explanation for the role of fluorides in the prevention of dental caries, and are in accord with previous biochemical and microbial observations.