Future Directions in Bioluminescence Research

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UNCLASSIFIED WORKGROUP SESSIONS

Laboratory Studies as a Complement to Ocean Measurements and Modeling
Discussion Leader: Michael I. Latz

There was a universal consensus among workshop participants that laboratory studies are not only of fundamental value in understanding the organismal basis of bioluminescence, but also are critical to specific programmatic goals such as ocean measurements, modeling, and new sensor approaches. Studies in shipboard and shore-based laboratories allow work on single species or individual organisms. Of great value to laboratory studies has been the successful laboratory culture of luminescent organisms, primarily bacteria and dinoflagellates. Use of laboratory cultures has greatly advanced the understanding of the physiology, behavior, chemistry, and genetics of key luminescent species. Laboratory studies allow us to identify and study processes that may be important in the field. Laboratory studies also allow "proof of concept" tests for new diagnostic tests and sensor approaches or design. The taxonomic enumeration of preserved water samples is crucial to determining the composition of plankton assemblages for the purpose of light budgets and modeling efforts.

What do we know?

• Based on studies of single identified organisms, both freshly collected and cultured, we have comprehensive knowledge of the light emission properties of many organisms from varied phyla, particularly planktonic forms. Measurements of emission spectra, photon flux, and flash kinetics have been made using state-of-the-art techniques and with standardized testing protocols.

• We know less about the luminescent response to relevant environmental stimuli. Recent studies of flow induced bioluminescence in dinoflagellates have identified stimulation thresholds, although little is known for other organisms.

• In select species, laboratory studies have identified sources of variability in bioluminescence because of changes in the physiological state of organisms due to environmental conditions.

• Historically, the chemistry of bioluminescence has been most extensively studied. We are beginning to understand the molecules involved in light production. The identification of novel luminescent substrates and proteins continues to provide new tools in biomedical research.

• For select marine organisms (bacteria and one dinoflagellate species) we have detailed knowledge of the genes involved in bioluminescence.

The workshop has identified the following organisms as key taxa because of their important contributions to bioluminescence in the littoral zone:

Dinoflagellates	Copepods
Lingulodinium polyedrum (photosynthetic)	Pleuromamma spp. (e.g., P. xiphias)
Protoperidinium spp. (heterotrophic)	Metridia spp. (e.g., M. lucens)
Noctiluca scintillans (heterotrophic)

Future needs

For key taxa, a comprehensive knowledge of their biology is needed to satisfy programmatic needs. For example, coupled population models require knowledge of life cycle dynamics and physiological constraints as well as behavior.

• In most cases there is an extensive knowledge base for only a single species or closely related group. Can we generalize from our limited knowledge base? It is important to undertake parallel investigations in other species so that we can identify how taxon specific is our available information.

• There is still a need for knowledge of the environmental and growth conditions that cause variability in light emission. For example, why are some strains of dinoflagellates luminescent while other strains of the same species are not? Are strain differences in bioluminescence due to genetic differences?

• There are exciting advances in biotechnology, which provide new opportunities for study. For example, DNA chips and in situ probes have the potential for real time identification of organisms based on their protein and genetic composition. Genetic information on the key taxa is sorely lacking. For example, the gene sequence for dinoflagellate luciferase is known from only one species.

• More studies using relevant levels of stimuli are needed. For example, flow studies with copepods can identify the fluid parameters stimulating their light emission. The complete transduction and signaling pathway has yet to be described in a single luminescent species.

• Intensive investigations require that organisms be established in laboratory cultures. This is generally possible for the dinoflagellates, but needs to be done for copepods.

• Detailed knowledge of the life cycles of key taxa are required. For example, when do dinoflagellates enter a sexual phase, and how does this affect population dynamics?

• Taxonomic enumeration of plankton samples will quantify the fraction of autotrophic and heterotrophic dinoflagellates for varied environmental conditions and may help reveal clues as to environmental and biological conditions regulating the composition of dinoflagellate assemblages.

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