We express our gratitude to J. A. Salas from the University of Oviedo for providing the pEM4 expression vector.Aculeacin A acylase from Actinoplanes utahensis produced by Streptomyces lividans revealed acylase activities that are able to hydrolyze penicillin V and several natural aliphatic penicillins. Penicillin K was the best substrate, showing a catalytic efficiency of 34.79 mM−1 s−1. Furthermore, aculeacin A acylase was highly thermostable, with a midpoint transition temperature of 81.5°C.This work was supported by grant BIO 2003-04832 from the Spanish Ministry of Education and Science.Peer reviewed