Title: Temperature-induced Transcriptional Responses of a Deep-biosphere Bacterium, Kosmotoga Subject Category: Evolutionary Genetics

1 olearia, illuminate its adaptation to growth from 20ºC to 79ºC 2 Abstract 1 7 Temperature is one of the defining parameters of an ecological niche, and ambient temperature change is 1 8 a physiological challenge faced by all living cells. Most organisms are adapted to growing within a 1 9 temperature range that rarely exceeds ~ 30°C, but the deep subsurface bacterium Kosmotoga olearia is 2 0 capable of growing over an extremely wide temperature range (20°C-79°C). To pinpoint genomic 2 1 determinants of this flexible phenotype, we compared transcriptomes of K. olearia cultures grown at its 2 2 optimal 65°C to those at 30°C, 40°C, and 77°C. We found that changes in temperature significantly affect 2 3 expression of 573 of 2,224 K. olearia genes. Notably, this transcriptional response elicits re-modeling of 2 4 the cellular membrane and changes in metabolism, with increased expression of genes involved in energy 2 5 and carbohydrate metabolism at high temperatures versus up-regulation of amino acid metabolism at 2 6 lower temperatures. Such massive effects on the transcriptome indicate that temperature response is a 2 7 complex polygenic trait. Moreover, at 77°C one third of the up-regulated genes are of hypothetical 2 8 function, indicating that many features of high temperature growth are unknown. Via comparative 2 9 genomic analysis of additional Thermotogae, we inferred that one of K. olearia's strategies for low 3 0 temperature adaptation is to increase gene copy number through both duplication and lateral 3 1 acquisition. Our finding of coordinated temperature-specific gene expression patterns, and by extension 3 2 temperature specific metabolism, suggests that Kosmotoga populations encounter variable environments, 3 3 probably through migration. Therefore, we conjecture that deep subsurface microbial communities are 3 4 more dynamic than currently perceived.