SYMBIOTIC ASSOCIATION OFPHOTOBACTERIUM FISCHERIWITH THE MARINE LUMINOUS FISHMONOCENTRIS JAPONICA:A MODEL OF SYMBIOSIS BASED ON BACTERIAL STUDIES

Abstract

Isolation of bacteria from the luminous organ of the fish M. japonica revealed that the organ contains a pure culture of luminous bacteria. For the 4 fish examined, all contained P. fischeri as their luminous bacterial symbiont. This is the 1st time that P. fischeri was identified in a symbiotic association. A representative isolate (MJ1) of the light organ population was selected for in vivo studies of its luminous system. Several physiological features suggest adaptation for symbiotic existence. MJ1 produced and responded to an inducer of luciferase that could accumulate in the light organ. The specific activity of light production was maximal under low, growth-limiting concentrations of O2. Unlike another luminous species (Beneckea harveyi), synthesis of the light production system of these bacteria is not catabolite repressed by glucose, a possible source of nutrition in the light organ. When grown aerobically on glucose these bacteria excrete pyruvic acid into the medium. This production of pyruvate is a major process, accounting for 30-40% of the glucose utilized and may serve as a form of regulatory and nutritional communication with the host.