Bioluminescence of green Noctiluca scintillans from the coastal waters of Kochi (southwest coast of India) and in vivo experiments on bioluminescence in response to mechanical stimuli and its diurnal variations

ABSTRACT

A bloom of green Noctiluca scintillans (GNS) was spotted as conspicuous bright blue coloured bioluminescence in the coastal waters of Kochi on 29 May 2019. The intense blue colouration was visible in the inshore waters, which decreased towards offshore waters. We conducted experiments to elucidate the response of N. scintillans to mechanical stimuli and its diurnal variations (photo-inhibition and circadian rhythm) through in vivo experiments. The bioluminescence was measured using a Luminometer in three modes of speed frequencies (low, medium and high). The results indicated that the bioluminescence increased with increase in cell abundance and mechanical stimuli with an emission of 5.3 ± 1.9 × 10³ Relative Light Units (RLU) at high levels of mechanical stimuli. To understand the diurnal fluctuations and circadian rhythm in N. scintillans, 20 l samples were maintained in light-exposed (natural day/night) and light-deprived conditions in duplicates for 24 h. Bioluminescence was measured at 3 hourly intervals during the photophase (6:00 h to 18:00 h) and scotophase (18:00 h to 6:00 h) in Luminometer. Results suggest that the light-exposed samples exhibited peak bioluminescence (4.6 ± 0.5 × 10³ RLU) during the photophase (at 15:00 h when the Photosynthetically Active Radiation was 810 µmol m⁻² s⁻¹). Therefore, bioluminescence was not photo-inhibited in green strains of N. scintillans. Contrary to the earlier studies, maximum bioluminescence in light-exposed samples was lower than light-deprived samples during the photophase/scotophase. These results suggest that though light influences bioluminescence, it does not regulate its endogenous circadian rhythm in bioluminescence in green N. scintillans.

KEYWORDS:

• Noctiluca scintillans
• bioluminescence
• mechanical stimuli
• diurnal variations
• photo inhibition
• circadian rhythm

Acknowledgements

The authors acknowledge the support and facilities provided by the director of Council of Scientific Industrial Research – National Institute of Oceanography (NIO), Goa & Scientist-in charge of Regional Centre, NIO Kochi. The authors are also grateful to Defense Research and Development Organisation – Naval Research Board, Govt. of India for the financial support through the Grant-in-aid project, GAP-3157. They are also thankful to Akshay V.S for the image of bioluminescence (Figure 8). This is NIO contribution number 6847.

Disclosure statement

No potential conflict of interest was reported by the authors.

Authors contributions

PA: Conceptualization, supervision, writing original draft, Research funding; VCR: Conceptualization, data curation, & data analysis, MNV: Conceptualization, supervision, AP: data analysis, MIP: data collection, data analysis, GP: data collection, data analysis, CMF: data analysis.

Data availability

All data are fully available without restriction.

Ethics statement

This study does not involve the use of human participants, specimens or tissue samples, or vertebrate animals, embryos or tissues.

Additional information

Funding

This work was supported by Naval Research Board, India [grant number: GAP3157].