Degradation of Cell Constituents by Starved Streptococcus lactis in Relation to Survival

Authors:
  • TTT. D. Thomas
    T. D. Thomas
  • RBR. D. Batt
    R. D. Batt
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Abstract
SUMMARY: Streptococcus lactis organisms were grown in lactose-limited batch culture and transferred, after washing, to phosphate buffer at the growth temperature. Soluble protein was released from viable organisms into the suspending buffer and the intracellular free amino acid pool declined steadily with the components appearing in the suspending buffer; a net increase in the total amount of free amino acid indicated some protein hydrolysis. RNA was hydrolysed, resulting in the release of u.v.-absorbing bases and ribose from the organisms. Conditions which promoted rapid RNA breakdown also produced rapid death rates and long cell division lags in surviving organisms. After 28 hr starvation in buffer containing Mg2+, the bacterial dry wt decreased by 26 %; loss of RNA, protein and free amino acids accounted for 10.3 %, 7.3 % and 2.7 % of the total bacterial mass loss. The products of polymer hydrolysis appeared to be released in an undegraded form into the external buffer and there was no appreciable formation of lactate, ammonia or volatile fatty acids, possibly indicating the absence of any important endogenous energy sources. There was no appreciable degradation of DNA or carbohydrate but phospholipid was broken down on prolonged starvation. No polyglucose or poly-β-hydroxybutyrate was detected in the organisms.

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