Search

In bioluminescent bacteria growing in shake flasks, the enzyme luciferase has been shown to be synthesized in a relatively short burst during the period of exponential growth. The luciferase gene appears to be completely inactive in a freshly inoculated culture; the pulse of preferential luciferase synthesis which occurs later is the consequence of its activation at the level of deoxyribonucleic acid transcription which is attributed to an effect of a "conditioning" of the medium by the growing of cells. Although cells grown in a minimal medium also exhibit a similar burst of synthesis of the luminescent system, the amount of synthesis is quantitatively less, relative to cell mass. Under such conditions, added arginine results in a striking stimulation of bioluminescence. This is attributed to a stimulation of existing patterns of synthesis and not to induction or derepression per se.

Chemical mutagens were used to obtain mutants deficient in bioluminescence in the marine bacterium Photobacterium fischeri strain MAV. Acridine dyes were effective in the production of dark mutants but not in the production of auxotrophs. These dark mutants were all of one type and appeared to contain lesions blocking the synthesis of luciferase. ICR-191 was especially effective in the production of aldehyde mutants, i.e., dark strains that luminesce when a long-chain aldehyde such as n-decanal is added to them. However, other mutant types were isolated after treatment with ICR-191. N-methyl-N'-nitro-N-nitrosoguanidine induced many bioluminescence-deficient types with respect to both the site of the lesion and the quantitative effect on the luminescent system. We characterized the dark and dim mutants with respect to their response to exogenous decanal, levels of in vivo and in vitro luminescence, and their rates of reversion to wild type. In addition, the luciferases of the mutant strains were examined by subunit complementation. On the basis of these analyses, we identified mutants which synthesize altered luciferase, strains which are deficient in synthesis of luciferase, and aldehyde mutants. The results of analysis of luciferase from the aldehyde mutants and the complementation studies indicate that the lesions in these strains are in the luciferase itself. Results obtained with wild-type cells grown in minimal medium, and aldehyde mutant cells grown either in complete or minimal medium, indicate that a "natural aldehyde factor" is involved in in vivo light emission. These same studies showed that the long-chain aldehyde(s) could only partially substitute for the natural "aldehyde factor." The possibility that the in vivo aldehyde factor is not a long-chain aldehyde is discussed.

The synthesis of the bioluminescent system of the marine luminous bacterium Photobacterium fischeri (strain MAV) is subject to both transient and catabolite repression by glucose, and this repression can be reversed by adenosine 3':5'-cyclic monophosphate. Catabolite repression is a mechanism that characteristically controls the synthesis of inducible enzymes involved in energy metabolism. The fact that luciferase synthesis is subject to this control suggests that whatever its role(s) may be, it cannot be considered a nonfunctional or vestigial enzyme system as previously hypothesized, and may actually have some more direct role in metabolic processes.