Tobacco cells (Nicotiana tabacum) are capable of growth on ammonia as a sole nitrogen source only when succinate, malate, fumarate, citrate, α-ketoglutarate, glutamate, or pyruvate is added to the growth medium. A ratio between the molar concentrations of ammonia to succinate (as a complementary organic acid) in the growth medium of 1.5 was optimal. Succinate had no effect on the rate of uptake of ammonia from the medium into the cells although it did affect the intracellular concentration of ammonia. However, the changes were not sufficient to explain inhibition of growth as being due to ammonia toxicity. The radioactivity from 14C-succinate was incorporated into malate, glutamate, and aspartate within 2 minutes. It appears that the role of organic acids is neither connected to ammonium transport nor to relief of ammonia toxicity, but may be related to the need for additional carbon skeletons for synthesis of amino acids.
Abstract A distributed parameter model for an airlift fermentor is presented. A riser represents the airlift fermentor, with plug flow in both gas and liquid phases, a well‐mixed section that acts as gas separator, and a downcomer with plug flow. The set of equations proposed makes possible both the understanding and design of the system. Macroscopic balances shows a behavior that is very close to conventional continuous stirred tank fermentor from the viewpoint of biomass production. In addition, the model predicts concentration profiles of biomass, substrate and oxygen in the liquid, and oxygen in the gas phase. This allows estimation of optimal gas flow rate for sufficient oxygen transfer with minimum energy input.
Abstract A comparison was made of the ability of several commercially significant yeast species to accumulate the vitamin thiamine. Saccharomyces cerevisiae accumulated two to four times as much thiamine as Candida tropicalis, Kluyveromyces fragilis , or Kluyveromyces lactis. Thiamine accumulation by yeasts in shaker flasks was two to three times greater than in a small fermentor.
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