Effects of penicillin G on mesosome-like structures in Agmenellum quadruplicatum.

Agmenellum quadruplicatum was treated with lethal doses of penicillin G (15 and 75 U/ml) and then examined by electron microscopy to observe changes that took place before lysis. Treatment for 30 min led to increases in the frequency and size of mesosome-like structures within the cells. There was a direct correlation between the magnitude of these increases and the concentration of penicillin G. The mesosome-like structures often were associated with division septa, and they resembled mesosomes reported in other cyanobacteria. It is suggested that these structures appeared and enlarged because synthesis of membrane material continued after wall (peptidoglycan) synthesis was inhibited by the drug.