18D-17 |
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A. E. DOBSON, Southeast Dairy Foods Research Center, North Carolina State Univ., Dept. of Food Science, Raleigh, NC 27695 and T. R. Klaenhammer, Southeast Dairy Foods Research Ctr., North Carolina State Univ., Dept. of Food Science, Box 7624, Raleigh, NC 27695-7624. Bacteriocins are antimicrobial peptides produced by a variety of gram-negative and gram-positive bacteria. Notably, peptide bacteriocins, like nisin and pediocin, produced by lactic acid bacteria (LAB), have been used widely as antimicrobials and food preservatives because of their broad spectrum of action against other gram-positive bacteria, including pathogens such as Listeria monocytogenes and Clostridium botulinum. Most bacteriocins produced by LAB show a range of inhibitory activity that is limited to closely-related species inhabiting the same environmental niche. Lactacin B is a chromosomally-encoded bacteriocin produced by Lactobacillus acidophilus NCFM. Genome sequencing of the NCFM chromosome identified an 8.7 kb region implicated in lactacin B production, processing, and export. The region was flanked by two strong terminators suggesting an operon structure. The putative operon comprises 11 putative genes with similarities to conventional bacteriocin machinery including a histidine kinase, response regulator, and a dedicated ABC transporter protein. Seven additional putative open reading frames with unknown functions were also identified in the suspected operon. Our objective was to investigate the role of this region in lactacin B production and processing. The gene encoding an ABC transporter protein was disrupted by homologous recombination with a targeted integration vector. The resulting mutant no longer inhibited the sensitive indicator strain, Lactobacillus delbrueckii ATCC 4797. Noting that the ABC transporter is located within the suspected 11 gene operon, the results indicate that this region encodes the structural, regulatory, processing, export, and immunity determinants responsible for lactacin B production.Characterization of the unknown genes residing within the lactacin B operon is expected to reveal important mechanisms through which this organism communicates and competes within the gastrointestinal tract.
Session 18D, Food Microbiology: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |