Antarctic marine actinomycetes from the Amundsen sea : An unexplored source of secondary metabolites for marine natural products = 아문센 해에서 분리된 남극 해양 방선균: 탐색되지 않은 해양 천연물의 이차 대사산물의 원천

다국어 초록 (Multilingual Abstract)

This study explores the diversity of actinomycetes isolated from the Amundsen Sea in Antarctica and investigates their potential to produce secondary metabolites. Actinomycetes have long been recognized as a major microbial source of diverse secondary metabolites in natural product research. The Antarctic marine environment, with its extreme conditions and limited exploration, offers a promising opportunity for discovering novel bioactive compounds. Marine sediment samples were collected from 17 different sites in the Amundsen Sea by the icebreaking research vessel ARAON. From these samples, a total of 25 actinomycetes were isolated in the laboratory. These isolates belonged to eight different genera, indicating a high level of phylogenetic diversity. Crude extracts of the isolated strains were evaluated for antibacterial activity and cytotoxicity, and several strains exhibited bioactivity. Among them, strain LMA743 showed weak activity in the initial screening. However, it demonstrated strong antibacterial and cytotoxic effects in the fractionated extracts obtained through large-scale fermentation. This study highlights the potential of Antarctic marine actinomycetes as a valuable source of bioactive secondary metabolites. In addition, it emphasizes the importance of further natural product research on Antarctic marine-derived actinomycetes.

목차 (Table of Contents)

• Contents
• List of Tables ⅳ
• List of Figures ⅴ
• Abstract ⅵ
• 1. Introduction 1
• 1.1. History of Natural Product Discovery from Actinomycetes 1
• 1.2.Marine Actinomycetes as a Source for Natural Product Discovery 3
• 1.3. Antarctic Environments as a Source of Novel Compounds 4
• 1.4. Microbial Diversity in Antarctic Marine Ecosystem 5
• 1.5. Research Objectives 6
• 2. Materials and Methods 7
• 2.1. Amundsen Sea and Sampling 7
• 2.1.1. Study Area 7
• 2.1.2. Sample Collection 7
• 2.1.3. Environmental Data of Amundsen Sea 8
• 2.2. Isolation of Actinomycetes 9
• 2.3. Salt Tolerance Test 10
• 2.4. 16S rRNA Gene Sequencing and Phylogenetic Analysis 10
• 2.5. Fermentation and Extraction 11
• 2.5.1. One-Liter Culture and Extraction for General Screening 11
• 2.5.2. Eighteen-Liter Culture and Extraction of LMA743 11
• 2.6. Bioactivity Screening 12
• 2.6.1. Antibacterial Screening: Growth Kinetics Assay 12
• 2.6.1.1. One-Liter Culture Antibacterial Screening 12
• 2.6.1.2. Antibacterial Screening of Eighteen-Liter Culture of LMA743 13
• 2.6.2. Toxicity Screening: Brine Shrimp Lethality Assay (BSLA) 14
• 3. Results 15
• 3.1. Marine Actinomycetes Isolated from Amundsen Sea Sediments 15
• 3.2. Phylogenetic Analysis 20
• 3.3. One-Liter Screening 22
• 3.3.1. Antibacterial Activity 22
• 3.3.2. Toxicity 23
• 3.4. Eighteen-Liter Screening with LMA743 23
• 3.4.1. Antibacterial Activity of LMA743 24
• 3.4.2. Toxicity of LMA743 25
• 4. Discussion 26
• 4.1. Marine Actinomycetes Isolated from Amundsen Sea Sediments 26
• 4.2. Phylogenetic Analysis 26
• 4.3. One-Liter Screening 27
• 4.4. Limitations of the Study 28
• 5. Conclusion 29
• References 30
• List of Supplementary Figures 37
• Acknowledgement 55