Bioluminescent bacteria emit luminescence through the expression
of a bacterial luciferase (lux) gene. Bacterial luciferase catalyzes
the oxidation of long-chain aliphatic aldehydes and in the process
emits blue–green light [104]. The use of bioluminescent bacteria in
short-term toxicity assays has been studied for more than 30 years
[105]. Initially, the marine bacterium Vibrio fischerii (Photobacterium
phosphoreum), in which bacterial bioluminescence was first
observed, was used directly [106,107]. The assays featured a ‘lightsoff’
mode, i.e., luminescence signals which should be emitted by
viable V. fischerii cells at a certain cell density “switch off” when
there are toxic compounds that affect the bacteria. Eventually, an
off-line toxicity assay system for measuring the bioluminescence of
V. fischerii (reconstituted from freeze-dried stock as part of the assay
kit) was developed and marketed commercially (as Microtox®),
and this has been an industrial standard method for rapid toxicity
screening [108]. The Microtox® assay performs acute toxicity tests
within 5–15 min [109], and can be measured not only by its proprietary
Microtox® equipment, but also on microplate luminometers