Microbes with the ability to grow in environments of pressures much greater than atmospheric pressure (0.1 MPa) compose a majority of all microbial biomass on this planet. Despite their prevalence, the molecular mechanisms of resistance to high pressure have yet to be precisely characterized. The study of piezophiles, organisms that grow optimally under high hydrostatic pressure, can further our understanding of these adaptations. In this work, we have investigated the effects of different hydrostatic pressures on gene expression and cellular morphology modulation in a deep-sea piezophilic bacterium able also to grow at atmospheric pressure: Photobacterium profundum. Key outer membrane proteins OmpH and OmpL are considered among the most variable in expression between pressure states, and so we specifically examined their transcription using GFP promoter fusions. The protein ToxR, thought to have a role in enacting pressure response and regulating OmpH and OmpL, was examined likewise for alterations in concentration and stoichiometry using a GFP fusion construct. Absolute copy number and concentration of GFP in both cases was quantified using scanning number and brightness (sN&B), a high-resolution microscopy technique based on detecting minute fluctuations in observed fluorescence within a small excitation volume. Fluorescence images collected from this technique were used to evaluate the morphologies of individual P. profundum cells, which too are altered as part of the pressure adaptation response. By imaging cells grown at 28.0 MPa and 0.1 MPa, changes in the expression of genes coding for OmpH and OmpL were observed, as were changes in concentration of ToxR proteins. Several distinct morphologies of P. profundum cells were also documented between certain growth conditions.
Whalen et al. (Sun,) studied this question.