Understanding more about bioluminescence is important on several fronts.
The first has to do with the different chemistries extracted from bioluminescent organisms. There are many different chemical combinations that produce light and some of these chemicals have proven to be tremondously valuable for such things as the testing of drugs to fight cancer and the testing for life on Mars. In other cases the organisms themselves can serve as bioassays for such things as the development of antibacterial agents or detecting toxic compounds in our waters, which is one way we use it at ORCA. One chemical in particular stands out because its discovery and applications were responsible for the awarding of the 2008 Nobel Prize in Chemistry. It is green fluorescent protein (GFP), isolated from the jellyfish Aquorea victori.. It’s been equated with the invention of the microscope in its impact on cell biology and genetic engineering!
The second has to do with what the number and variety of light emitting systems tells us about the evolution of bioluminescence. The ability to make light apparently evolved many different times during evolutionary history – at least 40 and maybe as many as 50 times – indicating this is a trait that obviously offers significant survival advantages. Molecular and genetic analyses of light emitting organisms are providing new instights into the mechanisms of evolution.
The third has to do with developing a better understanding of ecological relationships in the ocean. Because so many marine organisms are bioluminescent, measurements of stimulated bioluminescence in the oceans are valuable for determining the distribution patterns of different populations. Such measurements are useful over a wide range of scales, from kilometers down to centimeters.
Fine-scale measurements of stimulated bioluminescence in the ocean are made with instruments like this one (above. Known as a bathyphotometer or BP, this instrument pulls sea water, containing organisms, through a pipe into a light-tight chamber. There, a light detector measures the bioluminescence, stimulated by some turbulence-generating device like a paddle wheel. The light is measured in photons per second, or watts or sometimes in numbers of flashes stimulated. But what does this measurement mean?
Some bioluminescent organisms produce only a single flash, while others produce multiple flashes, and flash durations vary from less than 100 ms to many seconds. As a result the design of a bathyphotometer may have a profound impact on just how much light is measured in a particular body of water. This is because the photon flux measured by a bathyphotometer depends on such variables as the detection chamber volume, the flow rate through the chamber, the method of stimulation and the amount of prestimulation which might occur before the organisms reach the detection chamber. Some of this variability is evident in the different units of measurement that are used for different bathyphotometer designs.
To the left is the time course for a typical bioluminescent flash. It has a rapid onset (generally between 30 and 300 ms) followed by an exponential decay (generally taking between 100 ms and 1 s to decay to 3% of the peak intensity). In a long residence time BP, like that shown on the lower left, the total photon flux from the flash is measured, whereas in the short residence time BP on the middle right only a portion of the flash is measured. When the residence time of the bioluminescent organism in the detection chamber is long enough for a whole flash to occur, units of photons per unit volume are used. This is because under such circumstances the average photon flux measured by the light detector is a function of the concentration of bioluminescent organisms, the total photons per flash and the volumetric flow through the detection chamber. Therefore, in these cases the average photon flux (photon/s) is divided by the volumetric flow (volume/s) and results are reported in photons per unit volume. On the other hand, when the residence time in the detection chamber is short compared to the duration of the flash, then the average photon flux measured by the light detector is a function of the detection chamber volume rather than the volumetric flow. Under these circumstances the photon flux measured by the detector is divided by the chamber volume, rather than volumetric flow, and the results are reported as photons per second per unit volume. Although these various bathyphotometer designs are useful as relative indicators of plankton distribution patterns, they do not permit direct comparison of measurements made by different investigators, which is essential if bioluminescence is to become a standard oceanographic assay.
The U.S. Naval Oceanographic Office now uses the HIDEX-BP for routine monitoring of bioluminescence. HIDEX design principles have also been incorporated into a towed system (TOWDEX) and a moored system (MOORDEX). The basic design is such that direct comparison of measurements from these various systems is possible and bioluminescence can now be measured in conjunction with standard oceanographic measurements such as conductivity, temperature, depth, fluorescence and transmission.
Left is a vertical profile of stimulated bioluminescence measured in the Gulf of Maine with the HIDEX-BP. The complete profile was acquired in less than 10 minutes and gives a rapid assessment of the distribution of bioluminescent plankton relative to such environmental variables as temperature, salinity and chlorophyll concentration. Click on the button below to learn how we determine which organisms are responsible for these various bioluminescent peaks.