The secretory expression system of the protransglutaminase using C. glutamicum has already been reported (WO01/23591). Then, by using the plasmid vector pPKSPTG1 for secretory expression of protransglutaminase described in WO01/23591, each of the YDK010 strain and the YDK010ΔPBP1a strain was transformed. Each of the obtained transformants was cultured in the MM liquid medium (120 g of glucose, 3 g of magnesium sulfate heptahydrate, 30 g of ammonium sulfate, 1.5 g of potassium dihydrogenphosphate, 0.03 g of iron sulfate heptahydrate, 0.03 g of manganese sulfate pentahydrate, 450 μg of thiamine hydrochloride, 450 μg of biotin, 0.15 g of DL-methionine, and 50 g of calcium carbonate in a volume of 1 L with water, adjusted to pH 7.0) containing 25 mg/l of kanamycin at 30° C. for 72 hours. After completion of the culture, culture supernatant obtained by centrifuging each culture broth was subjected to reduced SDS-PAGE, and then stained with CBB R250 (produced by Bio-Rad). Secretion amounts of the protransglutaminase were determined according to the previous report (Protein Expr. Purif., 26:329-335), and the amounts were compared. As a result, the secretion amount of the protransglutaminase was significantly improved in the YDK010ΔPBP1a strain compared with that observed for the parent strain YDK010 (FIG. 8).
