Affiliation:
1. Laboratory of Food Microbiology and Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Leuven, Belgium
2. National Reference Centre (NRC) C. botulinum & C. perfringens, Scientific Institute of Public Health (WIV-ISP), Brussels, Belgium
Abstract
ABSTRACT
Group II nonproteolytic
Clostridium botulinum
(gIICb) strains are an important concern for the safety of minimally processed ready-to-eat foods, because they can grow and produce botulinum neurotoxin during refrigerated storage. The principles of control of gIICb by conventional food processing and preservation methods have been well investigated and translated into guidelines for the food industry; in contrast, the effectiveness of emerging processing and preservation techniques has been poorly documented. The reason is that experimental studies with
C. botulinum
are cumbersome because of biosafety and biosecurity concerns. In the present work, we report the construction of two nontoxigenic derivatives of the type E gIICb strain NCTC 11219. In the first strain, the botulinum toxin gene (
bont
/
E
) was insertionally inactivated with a retargeted intron using the ClosTron system. In the second strain,
bont
/
E
was exchanged for an erythromycin resistance gene using a new gene replacement strategy that makes use of
pyrE
as a bidirectional selection marker. Growth under optimal and stressed conditions, sporulation efficiency, and spore heat resistance of the mutants were unaltered, except for small differences in spore heat resistance at 70°C and in growth at 2.3% NaCl. The mutants described in this work provide a safe alternative for basic research as well as for food challenge and process validation studies with gIICb. In addition, this work expands the clostridial genetic toolbox with a new gene replacement method that can be applied to replace any gene in gIICb and other clostridia.
IMPORTANCE
The nontoxigenic mutants described in this work provide a safe alternative for basic research as well as for food challenge and process validation studies with psychrotrophic
Clostridium botulinum
. In addition, this work expands the clostridial genetic toolbox with a new gene replacement method that can be applied to replace any gene in clostridia.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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