Symbiotic relationship between a microalga, Pavlova viridis and associated bacteria

다국어 초록 (Multilingual 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.

목차 (Table of Contents)

• Table of Contents i
• List of Figures v
• List of Tables vii
• Introduction 1
• Materials and Methods 5
• Experimental design 5
• Microalga culture 6
• Isolation of bacteria 7
• Antibiotic resistance 7
• Axenic culture of Pavlova viridis 8
• Identification of bacterial isolates 10
• Identification of host algae 11
• Culture of bacterial isolate I3 15
• Algal growth assays with five bacterial isolates 17
• Algal growth assays with bacteria-free filtrates 18
• Growth promotion of alga and bacteria in co-culture 19
• Scanning electron microscopy (SEM) 21
• Results 22
• Isolation and identification of bacteria 22
• Antibiotic resistance test 34
• Cleaning of microalga 36
• Identification of the host 38
• Test for growth promotion of Pavlova viridis by isolated bacteria 41
• Growth and molecular characteristics of the bacterium I3 43
• Effects of temperature on the growth of Arthrobacter sp. 44
• Effects of NaCl concentration on the growth of Arthrobacter sp. 44
• Effect of pH on the growth of Arthrobacter sp. 44
• Growth promotion of bacteria and alga in co-culture 48
• Growth promotion of alga with bacteria-free filtrate 50
• Observation by SEM method 53
• Discussion 55
• Conclusion 60
• Acknowledgement 61
• References 62