Bacterial bioluminescence

The emission of light by biological species (bioluminescence) is a fascinating process found in diverse organisms such as bacteria, fungi, insects, fish and nematodes. In all cases the bioluminescent process is based on a chemiluminescent reaction in which the chemical energy is transformed into light energy. Although the underlying chemistry is as diverse as the range and distribution of light-emitting biological species, all bioluminescent processes require a luciferase, i.e. an enzyme catalyzing the chemiluminescent reaction, and a luciferin, which can be considered a coenzyme for the reaction. During the reaction the luciferin is generated in an excited state and serves as the emitter of light energy. In our study, we are interested in the bioluminescence of marine photobacteria. In these bacteria, luciferase is composed of an alpha/beta-heterodimeric protein, which binds reduced flavinmononucleotide (FMN). The reduced FMN reacts with molecular dioxygen to a reactive hydroperoxide intermediate with subsequent oxidation of a long-chain fatty aldehyde (e.g. tetradecanal) to the corresponding fatty acid. During this oxidation process, an excited flavin intermediate is generated which emits light centered at 490 nm. Some marine photobacteria possess an additional gene, luxF, encoding a protein similar to the beta-subunit of luciferase. This protein binds a myristylated flavin derivative where the C-3 atom of myristic acid is covalently attached to the 6-position of the flavin ring system. It was postulated that this flavin adduct is generated in the luciferase catalyzed bioluminescent reaction. Furthermore, it was speculated that luxF sequesters the myristylated flavin adduct in order to prevent inhibition of the luciferase. However, both hypotheses have not been tested on a biochemical or physiological level. Hence, we will identify the biochemical process yielding the flavin adduct and analyze the relationship to the bioluminescent reaction. Our approach will contribute to a more comprehensive understanding of the luciferase reaction and expand our knowledge to the functional role of luxF in bioluminescent marine photobacteria.

The emission of light by biological species (bioluminescence) is a fascinating process found in diverse organisms such as bacteria, fungi, insects, fish and nematodes. In all cases the bioluminescent process is based on a chemiluminescent reaction in which the chemical energy is transformed into light energy. Although the underlying chemistry is as diverse as the range and distribution of light-emitting biological species, all bioluminescent processes require a luciferase, i.e. an enzyme catalysing the chemiluminescent reaction, and a luciferin, which can be considered a coenzyme for the reaction. During the reaction the luciferin is generated in an excited state and serves as the emitter of light energy. In our study, we focused on the bioluminescence of marine photobacteria. In these bacteria, luciferase is a heterodimeric protein, which binds reduced flavinmononucleotide (FMN). The reduced FMN reacts with molecular dioxygen to a reactive hydroperoxide intermediate with subsequent oxidation of a long-chain fatty aldehyde (e.g. tetradecanal) to the corresponding fatty acid. During this oxidation process, an excited flavin intermediate is generated which emits blue light centered at 490 nm. Some marine photobacteria possess an additional gene, luxF, encoding a protein similar to one of the luciferase subunits. This protein binds a myristylated flavin derivative where the C-3 atom of myristic acid is covalently attached to the 6-position of the flavin ring system. In our research project we could demonstrate that this flavin adduct is generated in the luciferase catalysed bioluminescent reaction. Furthermore, it was shown that accumulation of this unusual flavin compound leads to the inhibition of luciferase and thus gradually leads to lower light emission. In order to prevent this, LuxF is produced and scavenges the myristylated flavin thus enabling the bacteria to maintain their light emission capacity. It is thus not surprising that the brightest light emitter marine bacteria all possess the LuxF protein. Therefore our investigations have also contributed to a better understanding of how bioluminescent bacteria have evolved to improve their competitiveness in a challenging environment.