An established method to measure microbial growth is to measure absorbance at 600 nm. Absorbance and light scattering increase with increasing number of particles, in this case the number of microbes.
In this application note, the growth of the deep sea bacterium Photobacterium profundum SS9 was analyzed with regard to hydrostatic and osmotic pressure.
Monitoring the OD600 using a BMG LABTECH microplate reader, it was revealed that hydrostatic pressure has a marked effect on the range of NaCl concentration at which P. profundum SS9 is able to grow. When the hydrostatic pressure was increased from 0.1 MPa to 28 MPa, growth of P. profundum SS9 was largely unaffected at intermediate salt concentrations (200-400 mM NaCl), but growth was strongly inhibited at higher NaCl concentration, compared to the results at 0.1 MPa. The optimum NaCl concentration range was 300-400 mM for both hydrostatic pressures tested.