Clostridia genomes have relatively low GC%, but contain regions with high local GC content. Using NCBI, the highest local GC regions in Clostridium botulinum and Clostridium novyi were determined to contain multiple tRNA genes. For comparison Mycobacterium leprae, which has nearly identical overall GC% to these Clostridia but lacks regions of high local GC%, has tRNA genes with the same GC content as the Clostridia. When defining bundling as two genes within 100 base pairs of each other, C. botulinum had 78% of the tRNA genes contained in 12 bundles with an average 5 genes per bundle and largest bundle of 22 genes, C. novyi had 78% in 11 bundles with an average of 6 genes per bundle and largest bundle containing 21 genes, and M. leprae had 27% bundled into 5 bundles of which none had more than 3 tRNA genes. The question that remains is what physiological benefit is gained by the Clostridia bundling the tRNA genes to give such large local GC% compared to the organismal total GC% while M. leprae keeps the tRNA genes distributed.

Difference of tRNA gene distribution between three low-GC bacteria

2019 Spring National Meeting

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