The role of a purine-specific nucleoside hydrolase in spore germination of Bacillus thuringiensis

A homologous gene (iunH) of a putative nucleoside hydrolase (NH), which had been identified from the exosporia of Bacillus cereus and Bacillus anthracis spores, was cloned from Bacillus thuringiensis subsp, kurstaki. Disruption of iunH did not affect the vegetative growth and sporulation of Bacillus thuringiensis, but promoted both inosine- and adenosine-induced spore germination. The inosine- or adenosine-induced germination rate decreased when the wild-type iunH gene was overexpressed in Bacillus thuringiensis. The iunH gene product was characterized as a purine-specific NH. The kinetic parameters of lunH with inosine as substrate were [K.sub.m]=399 [+ or -] 115 [micro]M, [k.sub.cat] = 48.9 [+ or -] 8.5 [s.sup.-1] and [k.sub.cat]/[K.sub.m]=1.23x[10.sup.5] [M.sup.-1] [s.sup.-1]. The optimal pH and temperature for lunH were found to be pH 6 and 80 [degrees]C. Meanwhile, the specific activity of inosine hydrolase in intact spores of the wild-type strain with inosine as substrate was 2.89 [+ or -] 0.23 x [10.sup.-2] [micro]mol [min.sup.-1] [(mg dry wt).sup.-1]. These results indicate that lunH is important in moderating inosine- or adenosine-induced germination of Bacillus thuringiensis spores.