Adaptation strategies of Pseudothermotoga species to hydrostatic pressure by transcriptional analyses
Pseudothermotoga elfii strain DSM9442 and P. elfii subsp. lettingae strain TMOT are hyperthermophilic bacteria. P. elfii is a moderate piezophile, isolated from an oil-producing well in Africa at a depth of more than 1600 m. P. lettingae is piezotolerant, isolated from a thermophilic bioreactor fed with methanol as the sole carbon and energy source. In this study, we analysed these bacteria at the genomic and transcriptomic levels. According to the hydrostatic pressure growth conditions the transcriptomic analyses revealed differentially expressed genes emphasizing amino acid and sugars metabolism and transport as the major hydrostatic pressure responding processes. Notably, this work highlights the central role of the amino acid aspartate as key intermediate of the pressure adaptation mechanisms of the deep strain P. elfii DSM 9442. In addition, several differentially expressed genes involved in the membrane and cell wall biosynthesis pathways may be linked to the chain formation morphotype previously described at high pressure for strain P. elfii DSM9442. Overall design: Pseudothermotoga cells were grown  in 120 mL flasks at the desired hydrostatic pressure (0.1, 20, 30 and 40 MPa for Pseudothermotoga elfii strain DSM9442 and 0.1 and 20 MPa for P. elfii subsp. lettingae strain TMOT) until reaching mid-exponential growth. Then, cells were harvested by centrifugation at 6800g for 15 min at 4°C; the pellet was resuspended in 400 µL of 10 mM Tris-HCl (pH 8.0) and spun for 2 min at 12000g. The supernatant was removed and the pellet frozen in liquid nitrogen before being placed in -80°C storage until use for RNA-seq analyses.