Dinoflagellate Bioluminescence

Introduction

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The topic must include one section about microbes (bacteria, viruses, fungi, or protists). This is easy because all organisms and ecosystems have microbes.

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Figure 1. Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.[1].

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Filename: PHIL_1181_lores.jpg
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Legend/credit: Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.
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Subscript: H₂O
Superscript: Fe³⁺

Section 1 Genetics

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Include some current research, with at least one image. Call out each figure by number (Fig. 1).

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Here we cite April Murphy's paper on microbiomes of the Kokosing river.

Section 2 Mechanism of Bioluminescence

Bioluminescence in dinoflagellates is triggered by physical agitation, which causes an influx of protons into specialized organelles called scintillons, which are where bioluminescence takes place. Scintillons will protrude into very acidic vacuoles, so when stress is applied a mechanotransduction pathway, where mechanical stimuli are converted to biochemical signals, is activated, causing an action potential along the vacuole and scintillon membranes. This action potential triggers the opening of voltage gated proton channels, allowing protons to flow from the acidic vacuole into the scintillons.

Dinoflagellates only produce light when a luciferase enzyme catalyzes the oxidation of a luciferin. However, in high pH environments the a-helices of luciferase block access of the luciferin substrate to the catalytic β-barrel where the oxidation occurs. However at a low pH, such as that caused by the influx of protons into the scintillons, the a-helices move out of the way, allowing the reaction to proceed. The exact mechanism of this is unproven, but the leading hypothesis suggests that it is due to the protonation of several histidines in the polypeptide, as well as a lysine residue. These protonations cause electrostatic repulsion between the histidine-cations, leading to the conformational change uncovering the active site in the β-barrel.

Once the active site is uncovered, luciferin is oxidized by luciferase. This causes the release of photons with a wavelength of about 475 nm, which is perceived by humans as a flash of blue light. How the actual production of light works, and why light is released instead of other types of energy, is not well understood.

A second form of regulation, possibly relating to the circadian rhythm which prevents luminescence during the day but encourages it during the night, is the luciferin binding protein (LBP). In some species, this protein binds to luciferin and only unbinds at low pH, creating a similar regulatory effect as described above. (cite)

Include some current research, with a second image.

Here we cite Murphy's microbiome research again.

Conclusion

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References

Edited by Dylan Ryznar, student of Joan Slonczewski for BIOL 116, 2024, Kenyon College.