In environmental conditions that differ too greatly from its
native ones, the marine bacteria may fail to respond biologically as
expected [16]. Thus, genetically modified bacteria with a lux gene
inserted have been constructed and used as alternative indicator
organisms [110]. In some engineered bacteria, the lux gene was regulated
by specific promoters that respond to environmental signals
and are not constitutively expressed. Thus, these bacteria feature a
‘lights-on’ mode, i.e, the luminescence signal increases when toxic
compounds induce the promoter [104]. In such instances, the bacterium
would, in effect, be serving as a whole-cell biosensor (which