R-040. IS-Mediated Genome Rearrangement and Adaptation in Experimental Populations of Methylobacterium

M-C. Lee, C. J. Marx;
Harvard Univ., Cambridge, MA.

Insertion sequence (IS) elements are an important source of genetic variation. Through transposition, IS elements can interrupt genes or alter gene expression. Moreover, homologous recombination often occurs between different copies of the same IS element, resulting in genome rearrangements such as deletions, duplications, and inversions. In an experimental evolution system with Methylobacterium extorquens AM1, substantial IS-mediated genome rearrangements have been found in 32 populations that have been evolved in one of four different nutrient regimes for 1500 generations. These events have included multiple, nearly parallel deletions removing a >500 kb region from a megaplasmid present in this strain. In general, competition assays and growth studies indicate a 15~32% improvement in fitness and growth rate in the selective environment without significant tradeoffs when tested in other nonselective environments. However, in one of the four nutrient regimes, there was extensive loss of growth on other substrates. Ongoing work is exploring the potential connection between the IS-mediated events, adaptation and specialization in order to better understand the dual role of IS elements as genome parasites that also shape their host’s genome toward a new niche.