Abstract: The present invention relates to a nucleus covered or coated with a film including one or more PHA. The invention also relates to a PHA, characterized in that it is of the type PHB-V, a film and a composition including the PHA. The invention further relates to a film or a composition including a PHA and zosteric acid or a bioactive molecule. The invention moreover relates to a surface, preferably a nucleus, covered with the film of PHA, a method for production thereof, and methods for grafting a pearl oyster and producing a pearl using this nucleus. Finally, the present invention relates to a method for reducing graft failure and/or for improving the quality of the pearl using the nucleus according to the invention.

Abstract: A nucleus coated with a film includes one or more exopolysaccharides (EPS) and optionally one or more bioactive molecules such as bactericidal or bacteriostatic agents, cicatrizing agents and/or anti-inflammatory agents. A method for obtaining the nucleus, in order to inhibit graft rejection in pearl oysters is also described.