R-056. The Dynamics and Genetic Adaptation to Salt Stress in Long-Term Experimental Evolution of Desulfovibrio vugaris Hildenborough

A. Zhou1,2, Z. He1,2, M. P. Joachimiak3,2, P. S. Dehal3,2, A. P. Arkin3,2, K. Hillesland4,2, D. Stahl4,2, J. D. Wall5,2, T. C. Hazen3,2, J. Zhou1,2;
1Univ. of Oklahoma, Norman, OK, 2Virtual Inst. for Microbial Stress and Survival, Berkeley, CA, 3Lawrence Berkeley Natl. Lab., Berkeley, CA, 4Univ. of Washington, Seattle, WA, 5Univ. of Missouri, Columbia, MO.

One of the greatest challenges in biology is to understand the interaction between genotype and environment to determine the fitness of an organism. With the recent advances in genome sequencing and high-throughput genomic technologies, now it is possible to link sub-cellular molecular/metabolic processes with the population-level processes, functions and evolution. Sulfate reducing bacteria Desulfovibrio vugaris Hildenborough (DvH) is an ideal model environmental organism to address such fundamental questions. In this study, we aim to investigate the long-term evolutionary responses, diversifications and adaptation of DvH to salt stress by mimicking the stress condition in the lab culture. LS4D and LS4D + 100 mM NaCl were used as medium for the control lines and stressed lines (6 lines each, from single colony based pure culture) respectively. Cultures were kept at 37oC and transferred every 48 hrs with one to one hundred dilutions. The phenotype of the cell lines on LS4D with higher salt concentration were tested periodically. The results demonstrated that the adaptation to salt stress is a dynamical process. The enhanced salt tolerance to higher salt (LS4D + 250 mM NaCl) of stressed lines was observed at 300 generations; which became more and more obvious with the increase of generations. The de-adaptation experiment on 500, 1000 and 1200 generation cell lines not only provided strong evidence that the phenotype was due to the genetic change instead of physiological adaptation, but also clearly showed the dynamic trend of the genetic adaptation- the genetic mutation became stable at 1000 generation. To further decipher the genetic mystery in behind, the gene expression profile of the 1000 generation were examined by DvH whole genome microarray. Some poly-cistronic operons such as hmcF-E-D-C-B-A, rrf2-rrf1, LysA-2-LysX and DVU3290-3291-3292 (glutamate synthase) were significantly up-regulated in stressed lines. Next, whole genome sequencing on selected colony will be performed to identify the beneficial genetic mutation and more colonies will be checked to confirm whether the mutations are stable or fixed.