When Streptococcus lactis was starved in phosphate buffer the intracellular amino acid pool was rapidly released into the external medium from the onset of starvation whereas lactic dehydrogenase and DNA appeared in the suspending buffer only as organisms began to lose viability. Addition of spermine enhanced survival and suppressed the release of ultraviolet-absorbing material.
Thin sections of Streptococcus lactis were examined by electron microscopy at intervals during starvation in a number of environments. Ribosome particles rapidly disappeared from organisms starved in the absence of Mg2+ and non-viable organisms remained structurally intact; in the presence of Mg2+ ribo-somes were retained but, after prolonged starvation, some organisms autolysed soon after the death rate increased. Addition of a suitable energy source maintained cell structures intact for a much longer period but again lysis occurred as the death rate increased. Starvation led to unfolding or extrusion of the mesosomes and dislocation of the nuclear material. The death rate of starved S. lactis organisms in phosphate buffer partly depended on the presence of Mg2+, which probably acted by promoting polymer stability, particularly RNA. In this environment, a suitable exogenous energy source further enhanced survival which may ultimately be a function of cell wall and/or membrane stability.
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