Evidence for a common gene pool and frequent recombinational exchange of the tbpBA operon in Mannheimia haemolytica, Mannheimia glucosida and Bibersteinia trehalosi

Lee, I. and Davies, R.L. (2011) Evidence for a common gene pool and frequent recombinational exchange of the tbpBA operon in Mannheimia haemolytica, Mannheimia glucosida and Bibersteinia trehalosi. Microbiology, 157(1), pp. 123-135. (doi: 10.1099/mic.0.041236-0)

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Abstract

The tbpBA operon was sequenced in 42 representative isolates of Mannheimia haemolytica (32), Mannheimia glucosida (6) and Bibersteinia trehalosi (4). Twenty-seven tbpB and 20 tbpA alleles were identified whilst the tbpBA operon was represented by 28 unique alleles that could be assigned to seven classes. There were 1566 (34.8% variation) polymorphic nucleotide sites and 482 (32.1% variation) variable inferred amino acid positions among the 42 tbpBA sequences. The tbpBA operons of serotype A2 M. haemolytica isolates are, with one exception, substantially more diverse than those of the other M. haemolytica serotypes and most likely have a different ancestral origin. The tbpBA phylogeny has been severely disrupted by numerous small- and large-scale intragenic recombination events. In addition, assortative (entire gene) recombination events, involving either the entire tbpBA operon or the individual tbpB and tbpA genes, have played a major role in shaping tbpBA structure and its distribution in the three species. Our findings indicate that a common gene pool exists for tbpBA in M. haemolytica, M. glucosida and B. trehalosi. In particular, B. trehalosi, M. glucosida and ovine M. haemolytica isolates share a large portion of the tbpA gene and this probably reflects selection for a conserved TbpA protein that provides effective iron-uptake in sheep. Bovine and ovine serotype A2 lineages have very different tbpBA alleles. Bovine-like tbpBA alleles have been partially, or completely, replaced by ovine-like tbpBA alleles in ovine serotype A2 isolates suggesting that different transferrin receptors are required by serotype A2 isolates for optimum iron uptake in cattle and sheep. Conversely, the tbpBA alleles of bovine-pathogenic serotype A1 and A6 isolates are very similar to those of closely related ovine isolates suggesting a recent and common evolutionary origin.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Davies, Dr Robert
Authors: Lee, I., and Davies, R.L.
College/School:College of Medical Veterinary and Life Sciences > School of Infection & Immunity
Journal Name:Microbiology
ISSN:1350-0872
ISSN (Online):1465-2080
Published Online:30 September 2010

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