The calorimetric response of the yeast Kluyveromyes fragilis was investigated for growth in continuous culture where N limitation was imposed on a C-limited culture. Calorimetric measurements were combined with off gas anal., measurements of biomass, substrate and product concns., elemental biomass compn., and heat prodn. to study the physiol. response of K. fragilis. Regions where both carbon and nitrogen limited growth, were found over a broad range of diln. rates and feed carbon-to-nitrogen ratios. The principle mechanism by which K. fragilis accommodated regions of C and N limitation was by partial decoupling of the anabolic and catabolic pathways. When the culture was only N-limited, increased decoupling of the 2 pathways was obsd. The principal effect of the decoupling was an increased catabolic consumption of glucose, generating an increased heat yield. The preferred way to process the excess glucose was through respiration but the cells were also capable of fermenting a small percentage of the excess glucose in specific cases where the dissolved O2 partial pressure approached zero. In addn., these results were qual. compared to similar studies on Saccharomyces cerevisiae. The 2 yeasts were similar in their ability to accommodate dual limitation by uncoupling anabolic biomass formation from substrate consumption. The 2 yeasts were dissimilar in how the catabolic substrate was processed. For S. cerevisiae the presence of a bottleneck in the respiration pathway dictated that the majority of the catabolic glucose consumption was by fermn. For K. fragilis, the lack of a bottleneck in the respiration pathway dictated that the majority of catabolic glucose substrate consumption was by respiration. [on SciFinder (R)]