2Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky pr. 47, 119991 Moscow, Russia; fax: (499) 135-5328; E-mail: firstname.lastname@example.org
3Research Center Borstel, Center for Medicine and Biosciences, D-23485 Borstel, Parkallee 22, Germany; E-mail: email@example.com
4Centre de Recherches du Service de Sante des Armees, BP 87, Avenue des Maquis du Gresivaudan 24, F-38702 La Tronche Cedex, France; E-mail: firstname.lastname@example.org
* To whom correspondence should be addressed.
Received October 6, 2009; Revision received October 30, 2009
A knockout mutant with a deletion in a quorum sensing system gene qseC was generated from the vaccine strain Francisella tularensis 15 by site-directed mutagenesis. The variant with the inactivated gene qseC differed from the parental strain in growth rate on solid nutrient medium but had the same growth dynamics in liquid nutrient medium. The mutation abolished almost completely the resistance of the vaccine strain to normal rabbit serum and its ability to survive in macrophages; in addition, the strain lost the residual virulence. A significant phenotypic alteration was observed in the lipopolysaccharide of F. tularensis. Particularly, the mutant strain synthesized no noticeable amount of the lipopolysaccharide with the high-molecular-mass O-polysaccharide, presumably as a result of impairing biosynthesis of the repeating unit, namely, a loss of the ability to incorporate a formyl group, an N-acyl substituent of 4-amino-4,6-dideoxy-D-glucose.
KEY WORDS: Francisella tularensis, tularemia, quorum sensing, gene qseC, site-directed mutagenesis, lipopolysaccharide