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  • Hazel Teague posted an update 1 year, 11 months ago

    Image analysis of bacterial cells was done using the software IMAGEJ (National Institutes of Health, Bethesda, MD) ( 30). In Fig.?2, we show three growth curves (OD as a function of time), represented by three different symbols, obtained in our experiments at P?= 1 atm and T?= 37��C. The starting OD for all the growth curves is ��0.05. The growth curves show an exponential growth regime followed by a saturation regime. The value of the saturation OD (<0.5) is smaller compared to the saturation OD (typically 1.0) reached when oxygen is not a growth-limiting buy Crizotinib agent. In the oxygen-limited environment, both the division time and saturation OD are affected. The biomass of bacterial cells at time t in the exponential regime can be written as equation(5) m(t)=m(0)et/��,m(t)=m(0)et/��,where m(0) is the biomass of bacterial cell at the beginning of the exponential phase and �� is the doubling time (which, effectively, is a measure of the timescale over which bacterial biomass is doubled). The value �� is a function of both pressure and temperature. Because focal volume is constant during the course of experiments, the OD(t) of bacterial solution at a given t in the exponential regime can be written as equation(6) OD(t)=OD(0)et/��,OD(t)=OD(0)et/��,where OD(0) is the optical density at the beginning of the exponential phase. In Fig.?2, we also show exponential fits (solid lines) and the value of doubling time ��?= 45 �� 5?min obtained by measuring the slope of log(OD) versus time in the exponential regime. Typical error in the measurement of �� in our experiments is ?10% of the value of ��. In Fig.?3, a and b, we show the growth curve for various pressures at T?= 31��C and T?= 34��C, respectively. We find that where the saturation is reached within the timescale of our experiments, the time profile of the growth curves show the typical characteristics of growth at P?= 1 atm and T?= 37��C. In Fig.?3, c and d, we show �� extracted from Fig.?3, a and b, for various pressures at T?= 31��C and 34��C, respectively. We find that ��(P) increases, and hence the rate of growth decreases, upon increasing pressure. We further find that the OD corresponding to the saturation regime decreases upon increasing pressure. Earlier studies on the effect of pressure on the total biomass production of different bacteria C 646 have found a similar decrease in total mass as a function of pressure ( 31). The doubling time ��(P) at a given temperature increases with pressure but shows a discontinuous jump at high pressures. We find that the discontinuous jumps in �� occurs between P?= 250 and 400 atm for all the temperatures studied in our experiments. To further characterize the low-pressure regime of ��, in Fig.?4, we show the doubling time ��(P) as a function of pressure for two different temperatures T?= 31��C and T?= 34��C on a linear-log plot.