Springer Online Journal Archives 1860-2000
Process Engineering, Biotechnology, Nutrition Technology
Summary A new methylotrophic strain (T15), which employs the ribulose monophosphate (RuMP) cycle of formaldehyde assimilation, was isolated on the basis of high in vitro activities of formaldehyde and formate dehydrogenases (19 and 678 mU per mg protein, respectively). Serial subculturing of the strain in batch cultures, on 4 g/l CH3OH for 6 months, led to loss of substantial percentages of the NAD-linked formaldehyde (25%) and formate (98%) dehydrogenases. The activities of these two enzymes were partially recovered when cells were grown continuously at very low dilution rate (0.03 h−1). We found large variations (40 to 1000%) in the activities of other key enzymes of carbon-substrate oxidation (both linear and cyclic) and assimilation, in batch cultures with pure and mixed substrates, and in continuous cultures of different dilution rates. Key intracellular reaction rates, including those of the cyclic and linear substrate oxidation, were measured in vivo using a 14C-tracer technique in both continuous and batch cultures. The results indicate significant variations in these reaction rates, particularly those of linear and cyclic carbon oxidation. Overall, the cyclic oxidation appears to be employed to a larger (although not predominant) extent in strain T15 compared with another RuMP strain (L3) we have previously examined. T15 exhibits high biomass yields (up to 0.63 g cells per g CH3OH) and growth rates (up to 0.46 h−1) on CH3OH in batch cultures. CH3NH2 can also be utilized as a substrate. In continuous culture, T15 could be grown at dilution rates up to 0.36 h−1 with a corresponding biomass yield of 0.4. Examination of a large number of data on the biomass yields of strains T15 and L3 reveals that the large variations in yields derive from the variable branching of carbon flow between linear and cyclic oxidation and assimilation, rather than changes in the biosynthetic efficiency of carbon incorporation into biomass.
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