Insights into temperature adaptation in the Thermotogae gained through transcriptomics and comparative genomics

• Author / Creator

  Pollo, Stephen MJ

• Thermophilic microbes are extremophiles that live at high temperatures. In order to survive and maintain function of their biological molecules, they have a suite of characteristics not found in organisms that grow at moderate temperatures (mesophiles) that range from the cellular to the protein level. These fundamental differences presumably present a barrier to transitioning between the two lifestyles, yet many lineages are thought to have transitioned between thermophily and mesophily at least once. Studying groups of closely related thermophilic and mesophilic organisms can provide insight into these transitions. The bacterial phylum Thermotogae comprises hyperthermophiles (growing up to 90°C), thermophiles (50-70°C) and mesophiles (<45°C), thus presenting an excellent opportunity to study bacterial temperature adaptation. One Thermotogae species, Kosmotoga olearia, grows optimally at 65°C but grows over an extraordinarily broad temperature range of ~25 - 79°C. To investigate how this bacterium can tolerate such an enormous temperature range, RNA-seq experiments were performed on cultures grown across its permissive temperature range. Multivariate analyses of the resulting transcriptomes showed that the temperature treatments separated into three groups: heat-stressed (77°C), intermediate (65°C and 40°C), and cold-stressed (30°C and 25°C). Among the genes differentially expressed, unsurprisingly, were genes with known temperature responses like chaperones, proteases, cold-shock proteins, and helicases. Intriguingly however, increased expression of genes involved in carbohydrate metabolism and transport at supra-optimal temperature, contrasted with increased expression of genes involved in amino acid metabolism and transport at sub-optimal temperature suggests global metabolism is changed by growth temperature. This may allow K. olearia to play distinct roles across a range of thermal environments. Among the differentially expressed genes in K. olearia are genes shared with mesophilic Mesotoga spp. but none of the other thermophilic Thermotogae. Many of these genes have inferred regulatory functions implying that large regulatory changes accompany low temperature growth. In agreement with this, more genes were found to be differentially expressed at low temperatures compared to optimal than at high temperatures compared to optimal in K. olearia. Further genomic comparisons between K. olearia and the related K. arenicorallina, which has a narrower growth temperature range of 35 - 70°C, identified 243 genes that could be important for the wide temperature range of K. olearia. Clarifying mechanisms by which Bacteria adapt to temperature changes in isolation can inform studies of complex microbial communities in environments that experience fluctuations in temperature as well as provide a starting place to predict the responses of microbial communities to long term temperature change.

• Subjects / Keywords

  • Mesophile
  • RNA-Seq
  • Thermotogae
  • Bacteria
  • Transcriptomics
  • Comparative genomics
  • Kosmotoga olearia
  • Thermophile
  • Temperature adaptation

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R30Z7150T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.