Distribution of luminous bacteria and bacterial luminescence in the equatorial region of the Indian Ocean

Abstract

The number and species composition of luminous bacteria in seawater and zooplankton samples collected in the equatorial region of the Indian Ocean (Long. 49 degrees -60 degrees E; Lat. 4 degrees N-6 degrees S) were studied. While luminous bacteria contributed to 0.17 to 3.57% of the total viable bacterial population in seawater those associated with zooplankton accounted for nearly 10% of the total population. It was also noticed that a symbiotic pattern of distribution existed in the depths between 10 and 500 m, and a free living pattern in the surface samples. Vibrio fischeri contributed to more than 45% of the total luminous bacteria collected for the seawater samples, while, V. harveyi was the dominant species (53%) associated with the zooplankton. Photobacterium leiognathi and P. phosphoreum were also isolated but not in significant numbers. The in situ bioluminescence of seawater was observed to be very weak with a maximum value of 0.021 light units. A ten thousand fold higher luminescence, compared to that of seawater, was noticed from the zooplankton samples. This may be due to the autoinduction of luciferase synthesis or the accumulation of autoinducer in the luminous microflora living in close association with zooplankton