ISSN:
1432-0614
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Summary High pressure/high temperature investigations on thermophilic methanogens require specific precautions to provide well-defined pH conditions in their culture media. Applying CO2 as carbon source, sufficient buffering capacity of the culture medium is of crucial importance in investigations involving elevated pressures. In order to separate pressure effects on the growth and reproduction of thermophilic methanogens from pressure-induced protonation/deprotonation and increased solubility of gaseous components, direct pH measurements in common culture media in the absence and in the presence of CO2 were performed at elevated temperature (65° C), and at pressures up to 100 MPa. Neutral phosphate buffer at high pressure shows a significant downward shift of its pH which is strongly enhanced in the presence of CO2. In minimal media containing acetate, carbonate, formate and phosphate in ≤100 mM concentrations, 120 mM HEPES is found to provide optimum pH stability: near neutrality the pH change upon CO2 saturation in the absence and in the presence of HEPES amounts to ΔpH=2.10 and 0.41, respectively; the corresponding pressure dependences are ΔpH/100 MPa=-0.26 and -0.07. As taken from these results, the apparent pressure dependence of the optimum growth ofMethanococcus thermolithotrophicus at 65° C in minimal medium reflects the pH shift below the cutoff point of growth (pH 5.5), rather than pressure-induced growth inhibition. At constant pH, elevated pressure up to 400 MPa is found to increase the rate and yield of growth; at the same time, alterations in the phenotype of the bacterium are observed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00694308
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