Effects of synthetic local anaesthetics on the growth of the cyanobacterium Synechococcus leopoliensis

The effects of procaine and some related agents on the growth rate of the cyanobacterium Synechococcus leopoliensis were investigated under photoautotropic growth conditions and the data compared with those for selected phytohormones. Low concentrations (0.1-1 muM) of synthetic local anaesthetics ( procaine, procainamide, tetracaine, lidocaine, dibucaine) enhanced photoautotrophic growth. Lidocaine was the most effective growth stimulant, followed in decreasing order by procainamide, tetracaine, dibucaine, and procaine. Increases in growth rate were comparable to those elicited by similar concentrations of the auxins indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid and of the cytokinin kinetin. Quantitative structure-activity relationships between the anaesthetics and phytohormones were sought. Score plots of principal components formulated from twelve molecular descriptors suggest that the proliferative effects evoked by the anaesthetics and phytohormones may result from similar affinities for binding receptor sites on the cyanobacterial cell surface. Cyanobacterial growth assays could therefore be utilised as screens for compounds with potential applications in agriculture and medicine.