12th International Symposium on Bioluminescence & Chemiluminescence

Symposium abstracts:

Stimulation of DNA repair as an evolutionary drive for bacterial bioluminescence

Czyz, Agata¹, Wegrzyn, Grzegorz^2,3

1. Laboratory of Molecular Biology (affiliated with the University of Gdansk), Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Kladki 24, 80-822 Gdansk, Poland

2. Department of Molecular Biology, University of Gdansk, Kladki 24, 80-822 Gdansk, Poland

Email: wegrzyn@biotech.univ.gda.pl

3. Institute of Oceanology, Polish Academy of Sciences, Sw. Wojciecha 5, 81-347 Gdynia, Poland

The origin of bioluminescence was considered a problematic question of the Charles Darwin theory of evolution. The problem is that it is generally believed that the function of bioluminescence is directly associated with the visual behaviour of organisms. If this were true, it should be no benefit for organisms that possess weakly luminescent systems, i.e. emitting low amounts of light. On the other hand it would be hard to believe that early luminescent systems were as efficient as currently existing ones, or that they appeared suddenly in their present forms. Therefore, the question is what was the evolutionary drive that led to establishment of weakly luminescent systems and their further improvement. Even more complicated problem arose when luminescence of free-living bacteria was considered. Bacteria are able to produce light but cannot sense this signal. Recently it was demonstrated that luminescence of a free-living marine bacterium, Vibrio harveyi, stimulates DNA repair, most probably by activation of the photoreactivation process. Moreover, it was shown that light emitted by Escherichia coli cells bearing V. harveyi luminescence genes on plasmids also stimulates DNA repair efficiently. Light emitted by these E. coli strains is of relatively low intensity and it is not visible by a naked eye. Thus, we asked whether the stimulation of DNA repair could be an evolutionary drive that ensured maintenance and development of early bacterial luminescent systems. To test this, we cultivated V. harveyi lux⁺ bacteria and lux mutants in mixed cultures. Initial cultures were mixed to obtain a culture consisting of 50% lux⁺ cells and 50% lux mutants. Then, bacteria were cultivated for several days and ratio of luminescent to dark bacteria was measured. Under these conditions, lux mutants became highly predominant within a few days of cultivation. This indicates that without a selective pressure the luminescence is a disadvantage for bacteria, perhaps due to consumption of significant portion of cell energy. However, when the same experiments were repeated but cultures were irradiated with low UV doses, luminescent bacteria started to predominate shortly after the first irradiation. We conclude that stimulation of photoreactivation could be the early evolutionary drive of bacterial bioluminescence, especially at stages when efficiency of luminescent systems was too weak to produce visible light but sufficiently high to stimulate DNA repair. It is plausible that after appearing of improved luminescent systems that produced light detected by animals, other evolutionary drives started to operate, which led to establishment of symbiosis between luminescent bacteria and animals.

This is a preprint of an article accepted for publication in Luminescence: Copyright 2001 John
Wiley & Sons, Ltd (Wiley website)