AMINO-ACID AND METAL CONTENT OF CRASSOSTREA-GIGAS SHELL INFESTED BY POLYDORA SP IN THE PRISMATIC LAYER INSOLUBLE MATRIX AND BLISTER MEMBRANE

The spionid polychaete Polydora sp. can live and reproduce inside the oysters' shell, excavating a U-shaped burrow the central portion of wh ich is filled with detritus and particles of dissolved shell. The oyst er responds by secreting an organic layer, confining the worm, and lat er covering it with calcitostracum. This process creates a characteris tic ''mud blister''. Crassostrea gigas were analysed for the organic m atrix amino acid content and 14 metals of the whole shell of normal oy sters and severely Polydora infested ones. Amino acid, DOPA and FT-Ram an analyses were also performed on isolated membranes from the charact eristic mud blister and on prismatic layer insoluble matrix (PLIM) of infested oysters, with the aim of detecting any differences between th e two organic matrices. Membranes and PLIM composition differ from who le normal shell organic matrix by having lower aspartate and glycine a nd higher levels of virtually all hydrophobic amino acids, especially alanine. There are no significant differences between membranes and PL IM in the ratio of charged to non polar amino acids, respectively 0.54 and 0.59. L-DOPA content is also similar in the two matrices with 0.4 5 (+/-0.18) and 0.57 (+/-0.30) ng.mg(-1) protein for PLIM and membrane s respectively. The FT-Raman spectra of membranes is very similar to t hat of PLIM, suggesting that they have identical composition. Zinc, ir on and manganese are significantly higher in infested than in normal s hells. Infested oysters can provide an excellent opportunity for inves tigating normal biological calcification processes.