Brachyspira spp. colonise the intestines of some mammalian and avian species and show different degrees of enteropathogenicity, according to Therese Håström at the Swedish National Veterinary Institute in Uppsala and co-authors there and at the Swedish University of Agricultural Sciences. In a paper published recently in BMC Genomics, they explain that Brachyspira intermedia can cause production losses in chickens and strain PWS/AT has become the fourth genome to be completed in the genus Brachyspira.

Fifteen classes of unique and shared genes were analysed in B. intermedia, B. murdochii, B. hyodysenteriae and B. pilosicoli. The largest number of unique genes was found in B. intermedia and B. murdochii. This indicates the presence of larger pan-genomes. In general, hypothetical protein annotations are overrepresented among the unique genes.

A 3.2-kb plasmid was found in B. intermedia strain PWS/AT. The plasmid was also present in the B. murdochii strain but not in nine other Brachyspira isolates. Within the Brachyspira genomes, genes had been translocated and also frequently switched between leading and lagging strands, a process that can be followed by different AT-skews in the third positions of synonymous codons.

The researchers in Uppsala also found evidence that bacteriophages were being remodeled and genes incorporated into them.

The accessory gene pool shapes species-specific traits, concluded Håfström and co-authors. It is also influenced by reductive genome evolution and horizontal gene transfer.

They added that gene-transfer events can cross both species and genus boundaries, and bacteriophages appear to play an important role in this process. A mechanism for horizontal gene transfer appears to be gene translocations leading to remodeling of bacteriophages in combination with broad tropism.

Reference

Håfström T., D.S. Jansson and B. Segerman. 2011. Complete genome sequence of Brachyspira intermedia reveals unique genomic features in Brachyspira species and phage-mediated horizontal gene transfer. BMC Genomics, 12:395. doi:10.1186/1471-2164-12-395

Further Reading

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Further Reading

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Find out more information on spirochaetosis caused by Brachyspira by clicking here.

September 2011