Evolution of the leukotoxin promoter in genus Mannheimia

Larsen, J., Pedersen, A., Davies, R.L. , Kuhnert, P., Frey, J., Christensen, H., Bisgaard, M. and Olsen, J. (2009) Evolution of the leukotoxin promoter in genus Mannheimia. BMC Evolutionary Biology, 9(121), pp. 1-12. (doi: 10.1186/1471-2148-9-121)

Abstract

<b>Background</b>: The <i>Mannheimia</i> species encompass a wide variety of bacterial lifestyles, including opportunistic pathogens and commensals of the ruminant respiratory tract, commensals of the ovine rumen, and pathogens of the ruminant integument. Here we present a scenario for the evolution of the leukotoxin promoter among representatives of the five species within genus <i>Mannheimia</i>. We also consider how the evolution of the leukotoxin operon fits with the evolution and maintenance of virulence. <b>Results</b>: The alignment of the intergenic regions upstream of the leukotoxin genes showed significant sequence and positional conservation over a 225-bp stretch immediately proximal to the transcriptional start site of the <i>lktC</i> gene among all <i>Mannheimia</i> strains. However, in the course of the <i>Mannheimia</i> genome evolution, the acquisition of individual noncoding regions upstream of the conserved promoter region has occurred. The rate of evolution estimated branch by branch suggests that the conserved promoter may be affected to different extents by the types of natural selection that potentially operate in regulatory regions. Tandem repeats upstream of the core promoter were confined to <i>M. haemolytica</i> with a strong association between the sequence of the repeat units, the number of repeat units per promoter, and the phylogenetic history of this species. <b>Conclusion</b>: The mode of evolution of the intergenic regions upstream of the leukotoxin genes appears to be highly dependent on the lifestyle of the bacterium. Transition from avirulence to virulence has occurred at least once in <i>M. haemolytica</i> with some evolutionary success of bovine serotype A1/A6 strains. Our analysis suggests that changes in <i>cis</i>-regulatory systems have contributed to the derived virulence phenotype by allowing phase-variable expression of the leukotoxin protein. We propose models for how phase shifting and the associated virulence could facilitate transmission to the nasopharynx of new hosts.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Davies, Dr Robert
• Authors: Larsen, J., Pedersen, A., Davies, R.L., Kuhnert, P., Frey, J., Christensen, H., Bisgaard, M., and Olsen, J.
• Subjects: Q Science > QH Natural history > QH345 Biochemistry
• College/School: College of Medical Veterinary and Life Sciences > School of Infection & Immunity
• Journal Name: BMC Evolutionary Biology
• Publisher: Biomed Central
• ISSN: 1471-2148
• ISSN (Online): 1471-2148
• Published Online: 29 May 2009
• Copyright Holders: Copyright © 2009 Larsen et al; licensee BioMed Central Ltd.
• First Published: First published in BMC Evolutionary Biology 9(121):66
• Publisher Policy: This is an Open Access article distributed under the terms of the Creative Commons Attribution License