The thnR gene is a negative transcription regulator of the thurincin H genetic cassette in Bacillus thuringiensis subsp.
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The thnR gene is a negative transcription regulator of the thurincin H genetic cassette in Bacillus thuringiensis subsp. morrisoni Luz E. Casados‑Vázquez1,2 · Dennis K. Bideshi3,4 · José E. Barboza‑Corona1,2
Received: 3 September 2016 / Revised: 15 September 2016 / Accepted: 21 September 2016 © Springer-Verlag Berlin Heidelberg 2016
Abstract Thurincin H is a bacteriocin synthesized by some strains of Bacillus thuringiensis. In this study, the thurincin H genetic cassette, which contains ten genes, from a Mexican strain of B. thuringiensis subsp. morrisoni (Btm) was cloned and sequenced. To study the function of the thnR gene component in the cassette, we generated various constructs with or without thnR for expression in Btm. All transformants harboring thnR in recombinant plasmids showed a decrease of ~15 to ~90 % in inhibitory activity against the target strain, Bacillus cereus 183. Importantly, a ~90 % reduction in inhibition occurred with Btm harboring a construct containing thnR alone, suggesting that ThnR, indeed, functions as a negative transcription regulator of the thurincin H cassette. Based on sequence homology, ThnR was classified as a member of the YtrA subfamily of the GntR superfamily of transcriptional regulators. Keywords Bacillus thuringiensis subsp. morrisoni · Thurincin H · Bacteriocin · thnR transcriptional regulator Communicated by Jorge Membrillo-Hernández. * José E. Barboza‑Corona [email protected] 1
Graduate Program in Biosciences, Life Science Division, University of Guanajuato Campus Irapuato-Salamanca, 36500 Irapuato, Guanajuato, Mexico
2
Food Department, Life Science Division, University of Guanajuato Campus Irapuato-Salamanca, 36500 Irapuato, Guanajuato, Mexico
3
Department of Natural and Mathematical Sciences, California Baptist University, 8432 Magnolia Avenue, Riverside, CA 92504, USA
4
Department of Entomology, University of California, Riverside, CA 92521, USA
Introduction Bacillus thuringiensis is a sporogenic Gram-positive bacterium with insecticidal properties owing to its synthesis of Cry (crystalline) and Cyt (cytotoxic) protein protoxins that accumulate as intracellular crystalline inclusions during sporulation (Palma et al. 2014). Bacillus thuringiensis also produces small peptides called bacteriocins that have bacteriostatic and bactericidal activities against clinically significant pathogens, and as such, these antimicrobial peptides show promise as chemotherapeutic agents (De la Fuente-Salcido et al. 2013). At present, the N-termini of eleven bacteriocins of B. thuringiensis have been partially sequenced, but the primary structure of only thurincin H and thuricin CD are well known (Rea et al. 2010; Lee et al. 2009). Previous studies have established that thurincin H and thuricin CD are ribosomally synthesized, posttranslationally modified, and activated for secretion. Due to their intramolecular thioether bonds that crosslink the sulfur atom of a cysteine residue with the α-carbon of an acceptor amino acid, they are classified
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