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

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.