Kinetics of light emission and oxygen consumption by bioluminescent bacteria

Oxygen plays a key role in bacterial bioluminescence. The simultaneous and continuous kinetics of oxygen consumption and light emission during a compl ete exhaustion of the exogenous oxygen present in a closed system has been investigated. The kinetics are performed with Vibrio fischeri, V harveyi, a nd Photobacterium phosphoreum incubated on respiratory substrates chosen fo r their different reducing power. The general patterns of the luminescence time courses are different among species but not among substrates. During s teady-state conditions, substrates, which are less reduced than glycerol, h ave, paradoxally, a better luminescence efficiency. Oxygen consumption by l uciferase has been evaluated to be approximate to 17% of the total respirat ion. Luciferase is a regulatory enzyme presenting a positive cooperative ef fect with oxygen and its affinity for this final electron acceptor is about 4-5 times higher than the one of cytochrome oxidase. The apparent Michaeli s constant for luciferase has been evaluated to be in the range of 20 to 65 nM O-2. When O-2 concentrations are as low as 10 nM, luminescence can stil l be detected; this means that above this concentration, strict anaerobiosi s does not exist. By n-butyl malonate titration, it was clearly shown that electrons enter the luciferase pathway only when the cytochrome pathway is saturated. It is suggested that, in bioluminescent bacteria, luciferase act s as a free-energy dissipating valve when anabolic processes (biomass produ ction) are impaired.