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Microbiology 154 (2008), 1333-1340; DOI  10.1099/mic.0.2007/014399-0
© 2008 Society for General Microbiology

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

Liang Liang1,2, Xihong He1,2, Gang Liu1 and Huarong Tan1

1 State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China
2 Graduate School of Chinese Academy of Sciences, Beijing 100039, PR China

Correspondence
Gang Liu
liug{at}sun.im.ac.cn
Huarong Tan
tanhr{at}im.ac.cn

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 IunH with inosine as substrate were Km=399±115 µM, kcat=48.9±8.5 s–1 and kcat/Km=1.23x105 M–1 s–1. The optimal pH and temperature for IunH were found to be pH 6 and 80 °C. Meanwhile, the specific activity of inosine hydrolase in intact spores of the wild-type strain with inosine as substrate was 2.89±0.23x10–2 µmol min–1 (mg dry wt)–1. These results indicate that IunH is important in moderating inosine- or adenosine-induced germination of Bacillus thuringiensis spores.

Abbreviations: NH, nucleoside hydrolase

The GenBank/EMBL/DDBJ accession number for the nucleotide sequence of iunH is EU072023.






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