Genetic variation of Renibacterium salmoninarum genes in infected salmonids

Graduation date: 2008Renibacterium salmoninarum is the causative agent of bacterial kidney disease in both\ud wild and farmed salmonid species worldwide. The genome of this pathogen has\ud significant synteny to the ubiquitous, soil-dwelling Arthrobacter spp. though it is 1.9 Mb\ud smaller, suggesting that reductive evolution has occurred. Recently, our group finished\ud sequencing and annotation of the R. salmoninarum American Tissue Culture Collection\ud 33209 strain, which has been cultured in vitro since 1974. The genome contained a\ud significant amount of inactivated genes caused by frameshift and extrachromosomal\ud elements. This led us to hypothesize that reduced evolutionary pressure due to lengthy\ud laboratory cultivation on the genome may account for the mutations found. To test this\ud hypothesis we analyzed four genes with different mutations typicalof mutations observed\ud throughout the genome using samples acquired from around the world. We used basic\ud molecular biology to elucidate the sequences and compared. We found that although the\ud ATCC 33209 strain had been cultured extensively in vitro, its sequence is representative\ud of what is found in nature. The mutations leading to inactivation of regions of the genome\ud suggests the pathogen R. salmoninarum has experienced reductive evolution