175.
Arthrobacter globiformis was grown under both carbon- and nitrogen-limiting conditions in a chemostat at a variety of growth rates. Under C-limiting conditions at 25°C, the true growth yield was 602 mg g
?1h
?1 and the specific maintenance rate 0.01 h
?1. However, at dilution rates less than 0.026 h
?1, the energy diverted for maintenance fell. Specific maintenance rates also fell as the growth temperature was lowered to a value of 0.0022 h
?1 at 10°C. The viability of populations at all temperatures remained above 80%. Under N-limiting conditions, viabilities were even higher and cell yields increased markedly as the dilution rate decreased, due to the formation of a glycogen-like reserve material. This made it difficult to calculate a meaningful specific maintenance rate.The chemical composition of the cells depended upon the nature of the medium and the growth rate, with exceptionally high carbohydrate levels, under N-limiting conditions where up to 65% of the cell material was carbohydrate at low growth rates. This accumulation of carbohydrate increased mean cell weights more than four-fold. If C-limited cells were starved, their weight decreased slowly and
Q(O
2) rates fell to values close to 1 within a few days. Nitrogen-limited cells when starved lost weight faster due to rapid utilization of the excess carbohydrate. Their viability also decreased and
Q(O
2) values only fell to about 3.6 after 28 days.The changes in maintenance requirement and rates of endogenous metabolism are discussed in the context of a fluctuating environment which might be found in soil.
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