The role of energy-spilling reactions in the growth ofKlebsiella aerogenes NCTC 418 in aerobic chemostat culture

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Abstract
When cell-saturating amounts of glucose and phosphate were added to steady state cultures ofKlebsiella aerogenes that were, respectively, glucose-and phosphate-limited, the organisms responded immediately with an increased oxygen consumption rate. This suggested that in neither case was glucose transport the rate-limiting process, and also that organisms must posses effective mechanisms for spilling the excess energy initially generated when a growth-limitation is temporarily relieved. Steady state cultures of mannitol- or glucose-limited organisms also seemingly generated energy at a greater rate than was required for cell synthesis since gluconate-limited cultures consumed oxygen at a lower rate, at each corresponding growth rate, than did mannitol- or glucose-limited cultures, and there-fore expressed a higherY o value. Thus, mannitol- and glucose-limitations must be essentially carbon (and not energy) limitations. The excess energy generated by glucose metabolism is one component of “maintenance” and could be used at lower growth rates to maintain an increased solute gradient across the cell membrane, imposed by the addition of 2%, w/v, NaCl to the growth environment. The maintenance rates of oxygen consumption ofK. aerogenes also could be caused to increase by adding glucose discontinuously (drop-wise) to a glucose-limited chemostat culture, or by exchanging nitrate for ammonia as the sole utilizable nitrogen source. The significance of these findings to an assessment of the physiological factors circumscribing energy-spilling reactions in aerobic cultures ofK. aerogenes is discussed.