New Perspectives Related to the Bioluminescent System in Dinoflagellates: Pyrocystis lunula, a Case Study

Unraveling a Receptor-Mediated Bioluminescence Signaling Pathway in Red Tide Algae

G protein-coupled receptors (GPCRs) are ubiquitous transmembrane proteins in multicellular life. Human vision, taste, and neuron activity are all mediated by GPCRs, and a large percentage of currently approved drugs target GPCRs. However, our understanding of GPCRs in single-celled eukaryotes is incomplete, and many of the components of GPCR signal transduction are underrepresented in protists. Previous works studying bioluminescent dinoflagellates-single-celled algae involved in coral reef endosymbiosis and toxic red tide blooms-implicate GPCRs in a signaling pathway for bioluminescence but have not elucidated the individual components comprising the pathway. Herein, we identified a novel GPCR in dinoflagellates-Bioluminescence-Inducing Receptor 1 (BIR1)-which plays a significant role in the signaling pathway for bioluminescence in red tide blooms in response to wave turbulence. Additionally, we identified a full endogenous G-protein complex and downstream effectors that are integral to known calcium signaling networks. Based on these identifications, we used knockdown and knockout techniques to demonstrate the integral role of BIR1 in bioluminescence and highlight its role in predator response and shear force-elicited GPCR signaling in red tide blooms. This advance opens avenues for red tide control and supports the existence of similar GPCR pathways involved in bloom toxicity dynamics.

Unveiling the potential of microbial bioluminescence for marine pollution monitoring: a review

Marine pollution threatens global ecosystems, underscoring the urgent need for robust and efficient monitoring systems. Microbial bioluminescence has emerged as a promising tool for pollution detection, offering unique advantages due to its simplicity, sensitivity, and ecological relevance. This review explores the fundamental principles of bacterial and dinoflagellate bioluminescence, ecological significance, and their applications in marine pollution monitoring. Bioluminescence-based detection systems are broadly categorized into whole-cell biosensors (WCBs) and enzyme-based biosensors. WCBs are further classified into recombinant organisms based WCBs (Class I and Class II WCBs) and wild-type organisms based WCBs (Class III WCBs), demonstrating distinct pollutant detection and stress-response monitoring capabilities. We highlight their potential to improve pollution monitoring strategies by critically evaluating these technologies. Integrating bioluminescence-based systems into current frameworks could significantly enhance the assessment of marine ecosystem health, facilitate timely pollution management, and support the conservation and sustainable use of marine resources.

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.

Bioluminescent Dinoflagellates as a Bioassay for Toxicity Assessment

Dinoflagellates bioluminescence mechanism depends upon a luciferin–luciferase reaction that promotes blue light emission (480 nm) in specialized luminogenic organelles called scintillons. The scintillons contain luciferin, luciferase and, in some cases, a luciferin-binding protein (LBP), which prevents luciferin from non-enzymatic oxidation in vivo. Even though dinoflagellate bioluminescence has been studied since the 1950s, there is still a lack of mechanistic understanding on whether the light emission process involves a peroxidic intermediate or not. Still, bioassays employing luminous dinoflagellates, usually from Gonyaulax or Pyrocystis genus, can be used to assess the toxicity of metals or organic compounds. In these dinoflagellates, the response to toxicity is observed as a change in luminescence, which is linked to cellular respiration. As a result, these changes can be used to calculate a percentage of light inhibition that correlates directly with toxicity. This current approach, which lies in between fast bacterial assays and more complex toxicity tests involving vertebrates and invertebrates, can provide a valuable tool for detecting certain pollutants, e.g., metals, in marine sediment and seawater. Thus, the present review focuses on how the dinoflagellates bioluminescence can be applied to evaluate the risks caused by contaminants in the marine environment.

Bioluminescence and Photoreception in Unicellular Organisms: Light-Signalling in a Bio-Communication Perspective

Bioluminescence, the emission of light catalysed by luciferases, has evolved in many taxa from bacteria to vertebrates and is predominant in the marine environment. It is now well established that in animals possessing a nervous system capable of integrating light stimuli, bioluminescence triggers various behavioural responses and plays a role in intra- or interspecific visual communication. The function of light emission in unicellular organisms is less clear and it is currently thought that it has evolved in an ecological framework, to be perceived by visual animals. For example, while it is thought that bioluminescence allows bacteria to be ingested by zooplankton or fish, providing them with favourable conditions for growth and dispersal, the luminous flashes emitted by dinoflagellates may have evolved as an anti-predation system against copepods. In this short review, we re-examine this paradigm in light of recent findings in microorganism photoreception, signal integration and complex behaviours. Numerous studies show that on the one hand, bacteria and protists, whether autotrophs or heterotrophs, possess a variety of photoreceptors capable of perceiving and integrating light stimuli of different wavelengths. Single-cell light-perception produces responses ranging from phototaxis to more complex behaviours. On the other hand, there is growing evidence that unicellular prokaryotes and eukaryotes can perform complex tasks ranging from habituation and decision-making to associative learning, despite lacking a nervous system. Here, we focus our analysis on two taxa, bacteria and dinoflagellates, whose bioluminescence is well studied. We propose the hypothesis that similar to visual animals, the interplay between light-emission and reception could play multiple roles in intra- and interspecific communication and participate in complex behaviour in the unicellular world.