Marine eukaryote bioluminescence: a review of species and their functional biology

Biochemical basis of endogenous bioluminescent springtail Lobella sauteri (Collembola)

Bioluminescence plays important roles among animals in both intra- and inter-species communication. A variety of bioluminescent organisms inhabit soil environments, even in areas where light penetration is minimal. However, due to the lack of a model system to study underground bioluminescence, the biology and molecular mechanisms underlying this phenomenon remain largely unknown. Springtails (Collembola) are representative soil animals, and we recently identified Lobella sauteri (Neanuridae) as a bioluminescent species. L. sauteri can be maintained over multiple generations under laboratory conditions on a single food source, the plasmodium Fuligo septica, with a generation time of approximately 3 months. Bioluminescence was observed in all developmental stages of L. sauteri in laboratory-raised populations. The light emission exhibited periodic changes and increased before ecdysis, coinciding with the whitening of its tubercles. The bioluminescent reaction in vitro requires a small molecular (luciferin) fraction, an enzyme (luciferase) fraction, adenosine triphosphate (ATP), and Mg2+. Comparative transcriptomic and biochemical analyses suggest that L. sauteri employs a novel endogenous bioluminescent molecular mechanism. We propose that L. sauteri provides a valuable research opportunity for investigating novel bioluminescence systems and underground light-based communication.

Insights into the bioluminescence systems of three sea pens (Cnidaria: Anthozoa): from de novo transcriptome analyses to biochemical assays

Bioluminescence is the production of visible light by living organisms. It occurs through the oxidation of luciferin substrates catalysed by luciferase enzymes. Auxiliary proteins, such as fluorescent proteins and luciferin-binding proteins, can modify the light emitted wavelength or stabilize reactive luciferin molecules, respectively. Additionally, calcium ions are crucial for the luminescence across various species. Despite the large phylogenetic distribution of bioluminescent organisms, only a few systems have been comprehensively studied. Notably, cnidarian species of the Renilla genus utilize a coelenterazine-dependent luciferase, a calcium-dependent coelenterazine-binding protein and a green fluorescent protein. We investigated the bioluminescence of three sea pen species: Pennatula phosphorea, Anthoptilum murrayi and Funiculina quadrangularis (Pennatuloidea, Anthozoa). Their light-emission spectra reveal peaks at 510, 513 and 485 nm, respectively. A coelenterazine-based reaction was demonstrated in all three species. Using transcriptome analyses, we identified transcripts coding for luciferases, green fluorescent proteins and coelenterazine-binding proteins for P. phosphorea and A. murrayi. Immunodetection confirmed the expression of luciferase in P. phosphorea and F. quadrangularis. We also expressed recombinant luciferase of A. murrayi, confirming its activity. We highlighted the role of calcium ions in bioluminescence, possibly associated with the mechanism of substrate release at the level of coelenterazine-binding proteins. The study proposes a model for anthozoan bioluminescence, offering new avenues for future ecological and functional research on these luminous organisms.

Availability and occurrence of coelenterazine in a Swedish fjord to maintain Amphiura filiformis bioluminescence

The bioluminescent European brittle star Amphiura filiformis produces blue light at the arm-spine level thanks to a biochemical reaction involving coelenterazine as substrate and a Renilla-like luciferase as an enzyme. This echinoderm light production depends on a trophic acquisition of the coelenterazine substrate. Without an exogenous supply of coelenterazine, this species loses its luminous capabilities. Moreover, this species was recently shown not to produce coelenterazine storage forms. As an infaunal suspensive feeder, A. filiformis is assumed to find enough substrate to maintain its bioluminescence capabilities efficiently. To date, no studies have investigated the putative source of coelenterazine in the brittle star diet. A combined analysis using listing based on visual observations and metabarcoding on the planktonic communities highlights planktonic species known as light emitters using coelenterazine. Besides, the A. filiformis stomach content was analyzed seasonally via metabarcoding technique, and coelenterazine-related preys were underlined. Results provide evidence of the presence of preys containing coelenterazine in the fjord environment and within the stomach content of the ophiuroid throughout the year. The results are consistent with the demonstration of the trophic acquisition of luminous capabilities in A. filiformis and give a new step by underlying the constant presence of coelenterazine suppliers throughout the year for the luminescence reaction occurring within this species.