Long‐term exposure to elevated temperature leads to altered gene expression in a common bloom‐forming cyanobacterium

Cyanobacteria have a strong potential to compete well under elevated temperatures. Understanding how they acclimate and evolve under climatic stressors can help us accurately predict their response to forecasted future conditions. However, it is unclear whether increased temperature results in microevolution and/or changes in gene expression. This is the first study to investigate how long‐term exposure under increased temperature influences cyanobacterial genomes. Here, we cultivated three strains of Microcystis aeruginosa (M10, M11, and M12) under two temperature conditions, ambient (22°C) and high‐temperature (26°C) for 2 yr and subsequently sequenced the full genomes. The six genomes were then compared to a reference genome and analyzed for single‐nucleotide polymorphisms, from which the mutation rate was calculated to see if temperature influenced the prevalence of gene changes. Furthermore, we investigated how temperature impacted the gene expression of six genes involved in thermal tolerance and heat shock response. We found that M. aeruginosa exposure to high temperatures demonstrated a stronger expressional response with genes associated with heat shock and thermal tolerance due to exposure to elevated temperature. Although the functionality of many genes encoding for the carbon concentrating mechanisms, nutrient metabolism and secondary metabolites were unaffected, temperature could be a possible driver of genetic change due to enhanced mutation rates. Yet, differing patterns in M10 exposed to high temperatures suggests strain specifics components are also a factor. These patterns suggest changes in plasticity, which would allow for M. aeruginosa to respond rapidly to changes in temperature and to be resilient to environmental change.