7-Amino cephalosporanic acid (7-ACA), which is currently obtained by chemical deacylation from cephalosporin C (CPC), is a major intermediate for industrial production of beta-lactam antibiotics. 7-ACA can also be produced from CPC by enzymatic route including two-step and one-step procedures. In our research, an ecs gene coding for CPC acylase was synthesized and cloned into pET-28a(+) to construct an E. coli expression plasmid pYG232. E. coli BL21(DE3) bearing pYG232 was induced by IPTG and successfully expressed the recombinant ECS (88.9 kDa). Under the optimal conditions: 0.5 mg/ml purified ECS protein, 5 mg/ml CPC, 100 mM Tris-Cl (pH 9.6), supplement with 7 mM Zn2+, slightly shaking for 6 h at 25 degrees C, the transformation productivity was 54.4%. Then, ecs was cloned downstream of an A. chrysogenum endogenous promotor, PpcbC, to construct pYG233 for expression in A. chrysogenum. pYG233 was introduced into a CPC high-producer via integrative transformation of protoplasts. Two independent bleomycin-resistant transformants were investigated by PCR, Southern blotting, quantitative RT-PCR, western blotting, and fermentation. Although these two transformants both have one copy of integrated ecs, they showed different expression level of ECS protein and 7-ACA production. When concentration of CaCO3 was reduced to 50 mM, ZnSO4 was increased to 7 mM, CuSO4 was eliminated from the fermentation media, and the pH was adjusted to 8.0 at day 4 during fermentation, 7-ACA production of one of the transformants could reach 1701 mu g/ml, indicated that more than 30% of CPC produced by this high-producer have been transformed into 7-ACA directly in vivo. This is the highest 7-ACA production by direct fermentation ever reported.