Influence of methylheptenone and related phytoplankton norcarotenoids on heterotrophic aquatic bacteria.

Certain norcarotenoids, which have recently been found as excretion products of freshwater cyanobacteria and algae, are potent inhibitors of different metabolic functions in heterotrophic bacteria. 6-Methylhept-5-en-2-one showed the strongest effects and acted as a noncompetitive inhibitor of both glucose uptake and respiration by aquatic isolates of Chromobacterium lividum and Arthrobacter sp. Inhibition of the heterotrophic potential of glucose uptake by 6-methylhept-5-en-2-one was characterized by considerably lower inhibitor constants for bacterial cultures (Ki = 0.4 and 1.6 microM) than for a river water sample (Ki = 186.0 microM).