A gene encoding alanine racemase is involved in spore germination in <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis>

Alanine racemase is a major component of the exosporium of Bacillus cereus spores. A gene homologous to that of alanine racemase (alrA) was cloned from Bacillus thuringiensis subsp. kurstaki, and RT-PCR showed that alrA was transcribed only in the sporulating cells. Disruption of alrA did not affect the growth and sporulation of B. thuringiensis, but promoted l-alanine-induced spore germination. When the spore germination rate was measured by monitoring DPA release, complementation of the alrA disruptant reduced the rate of l-alanine-induced spore germination below that of even wild-type spores. As previously reported for spores of other Bacillus species, d-alanine was an effective and competitive inhibitor of l-alanine-induced germination of B. thuringiensis spores. d-cycloserine alone stimulated inosine-induced germination of B. thuringiensis spores in addition to increasing l-alanine-induced germination by inhibiting alanine racemase. d-Alanine also increased the rate of inosine-induced germination of wild-type spores. However, d-alanine inhibited inosine-induced germination of the alrA disruptant spores. It is possible that AlrA converted d-alanine to l-alanine, and this in turn, stimulated spore germination in B. thuringiensis. These results suggest that alrA plays a crucial role in moderating the germination rate of B. thuringiensis spores.