Mechanism of toxicity of putrescine in Anacystis nidulans.

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Abstract
Putrescine is lethal to the cyanobacterium A. nidulans at extracellular pH values at which significant concentrations of the nonprotonated diamine rapidly diffuse into the cell and accumulate as the charged form. Although over 98% of the accumulated putrescine is not metabolized, a small fraction is rendered trichloroacetic acid-insoluble and about 90% of this is bound as putrescine to proteins and cell structures. Various synthetic functions were studied in the presence of a bacteriostatic (40 .mu.M) and a bacteriocidal (150 .mu.M) concentration of putrescine at pH 9.5. Under lethal conditions, protein synthesis was completely inhibited after 45 min and CO2 fixation after 100 min, whereas nucleic acid synthesis was less affected. Spermidine was lost from the cell and its synthesis was arrested. These functions were much less inhibited at 40 .mu.M putrescine. Ribosomes from putrescine-killed cells were irreversibly dissociated into 30S and 50S subunits. Some putrescine (1-4 molecules) cosedimented with each subunit.