摘要或動機

Azotobacteraceae 為一單棲固氮菌科，包含Azotobacter 與Azomonas 兩菌屬，在農業上可用來改善缺氮的貧瘠土壤。在分離土壤中的Azotobacteraceae 時，發現非單棲固氮菌與單棲固氮菌間可能具有共生的情形。我們利用優勢培養(缺氮)的方法篩選土壤中的Azotobacteraceae，將優勢培養後所生成的菌落稀釋104~106倍後，能有效分離Azotobacter 與Azomonas，然而低於此稀釋倍率則會形成混合菌落，其中可同時發現單棲固氮菌與非單棲固氮菌存在，推測某些非固氮菌在優勢培養過程中可能可從單棲固氮菌獲得氮源，與之共生。此外亦從菌種形態的差異並配合顯微螢光雜合技術(fluorescence in situ hybridization, FISH)、分子遺傳標記(16S-rDNA)等方式，分析土壤中的Azotobacteraceae，探討單棲固氮菌及其他非單棲固氮菌在培養基上的生長情形、比例及親緣關係。The family Azotobacteraceace is group of free-living nitrogen-fixing bacteria that is found in soil. Two genera are within this family: Azotobacter and Azomonas. Agriculturally, it is often used to improve fertility for nitrogen deficient barren lands. We analyze the Azotobacteraceace according to molecular biology and traditional taxonomy. We used an enrichment procedure to culture the bacteria, and diluted it repeatedly. We found it most suitable to dilute it 104~106 times to best separate Azotobacter from Azomonas. If the concentration were to be higher than this, mixed flora containing many different bacteria species would be found. Moreover, we noticed that non nitrogen-fixing bacteria, symbiotic nitrogen-fixing bacteria, and free-living nitrogen-fixing bacteria would form a single colony on a nitrogen-deprived medium. This implies that a symbiotic relationship may exist between nitrogen-fixing bacteria and non nitrogen-fixing bacteria. We also discuss the growing situation, the group proportion, and the relationships between free-living nixtron fixing bacteria and other bacteria by morphology, fluorescence in situ hybridization (FISH), and molecular biology.