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Applied and Environmental Microbiology, August 2004, p. 4784-4791, Vol. 70, No. 8
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.8.4784-4791.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Characterization of Two Bacillus thuringiensis Genes Identified by In Vivo Screening of Virulence Factors

Unité Génétique Microbienne et Environnement, Institut National de la Recherche Agronomique, La Minière, 78285 Guyancourt Cedex,¹ Groupe Génétique et Physiologie des Bacillus pathogènes, Institut Pasteur, 75724 Paris Cedex 15, France²

Received 12 February 2004/ Accepted 19 April 2004

Bacillus thuringiensis vegetative cells are known to be highly pathogenic when injected into the hemocoel of susceptible insect larvae. This pathogenicity is due to the capacity of B. thuringiensis to cause septicemia in the host. We screened a B. thuringiensis mini-Tn10 insertion library for loss of virulence against Bombyx mori larvae on injection into the hemocoel. Three clones with attenuated virulence were isolated, corresponding to two different mini-Tn10 insertions mapping to the yqgB/yqfZ locus. Single disruptions of the yqgB and yqfZ genes did not affect virulence against B. mori. In contrast, the inactivation of both genes simultaneously reproduced the effect of the mini-Tn10 insertion and resulted in a significant delay to infection. The double yqgB yqfZ mutant was also nonmotile, and its growth was affected at 25°C. We analyzed lacZ transcriptional fusions and detected promoter activity upstream from yqgB at 25 and 37°C. Overall, our findings suggest that the yqgB and yqfZ genes encode adaptive factors that may act in synergy, enabling the bacteria to cope with the physical environment in vivo, facilitating colonization of the host.