Symbiotic relationship between a microalga, Pavlova viridis and associated bacteria

Abstract

The symbiotic relationship between the flagellate microalga Pavlova viridis and its associated bacteria was investigated. The axenic culture of P. viridis was obtained by repeated treatment of the microalga with antibiotic cocktail. Axenic status was confirmed after sub culturing three times in sterile f/2 medium without antibiotic. The axenic alga was then co-inoculated with bacteria isolated from the alga to test the growth promotion of the algae. All bacterial isolates promoted the growth of P. viridis and bacterial isolate I3 was the most effective among the five tested bacteria. The cell numbers of microalga was significantly higher than that of control culture. The I3 isolate was further characterized and sequence analysis of the 16S rRNA of I3 isolate revealed 97% nucleotide sequence similarity with that of Arthrobacter sp. The optimum growth condition of Arthrobacter sp. was 37˚C, pH 7 and NaCl 1%. The growth of I3 isolate was also increased effectively by co-culturing with P. viridis, showing a symbiotic relationship between microalga and its associated bacterium. The association between microalga and bacterium was confirmed by scanning electron microscopy.