台灣地熱區兩新種嗜熱菌 (Chelatococcus 類似細菌及 Mesorhizobium 屬細菌) 之研究

Abstract

從台東縣上里溫泉以及綠島朝日溫泉區域，分離篩選出六株嗜熱菌，經過初步之 16S rRNA gene 序列分析比對，可將這些菌株歸屬於 Chelatococcus 以及 Mesorhizobium 兩群。第一群均由上里溫泉分離出，包括 NTU-1599、NTU-1600 以及 NTU-1601 與 Chelatococcus asaccharovorans DSM 6462T 最相似。第一群分離菌株為好氧菌呈現黃色菌落，為具有移動性之格蘭氏陰性桿菌，最適生長溫度為 50 oC (生長溫度範圍介於 30-55)，且可生長於含鹽 6 % 之培養基，DNA 之 mol% G+C 組成為 64.2-64.7。另外， 第一群分離菌株為桿菌且不能利用 NTA 為碳源。這兩個主要特性可以很容易將它們與參考菌株 C. asaccharovorans 區分開來。根據 16S rRNA gene 序列比對相似度(96.55-96.83 %) 、 DNA-DNA 雜合反應結果 (8.5-17.5 %) 以及形態、生理生化等相關分析結果，初步判定第一群分離菌株為 Alphaproteobacteria 中的新菌種且可能為一新菌屬。 第二群皆由綠島朝日溫泉分離出，包括了 NTU-1636、NTU-1642 以及 NTU-1646 與Mesorhizobium loti DSM 2626T相似。第二群分離菌株為好氧菌具移動性，呈現黃色菌落，為具單鞭毛革蘭氏陰性桿菌，生長溫度範圍為30-55 oC (最適生長溫度為 40-50 oC)，可於15 % NaCl 之條件下生長。 另外，第二群的分離菌株與 M. loti皆可生長於不含氮的培養基中。第二群分離菌株之DNA 之 mol% G+C 組成為61.7-62.4。根據 DNA-DNA 雜合反應 (3.0-13.3 %) 和16S rRNA gene 序列分析結果(95.27-95.49 %) 以及生理生化等相關特性，可初步判定第二群分離菌株為 Mesorhizobium 屬之新種菌株。

Six thermophilic bacteria were isolated from hot springs locating in the eastern region of Taiwan. The 16S rRNA gene sequence analysis indicated that these strains belonged to Alphaproteobacteria and could be classified into two groups: genus Chelatococcus and genus Mesorhizobium. Group I including strains NTU-1599, NTU-1600 and NTU-1601 isolated from hot springs in the Shangli area, Taitung county were closely related to Chelatococcus asaccharovorans DSM 6462T. Group I isolates were aerobic, yellow-pigmented, Gram-negative motile rods. The optimal growth temperature of isolates was 50 ℃ (tempterature range 30-55 ℃). Group I isolates could grow in the higher concentration of NaCl up to 6 % (w/v). The mol% G+C contents of the isolates were 64.2-64.7. The major differences between group I and the reference organisms were that group I isolates were rods and could not utilize NTA while the C. asaccharovorans was cocci and could utilize NTA (nitrilotriacetatic acid). According to the DNA-DNA homology (8.5-17.5 %), the 16S rRNA gene sequence analysis between the isolates and reference strain (96.55-96.83 %) as well as morphological, physiological, biochemical and chemical analyses indicated that group I isolates might be a novel genus within the Alphaproteobacteria. Group II including strains NTU-1636, NTU-1642 and NTU-1646 isolated from hot springs in the Lutao area, Taitung county were closely related to Mesorhizobium loti DSM 2626T. Those isolates were aerobic, motile, yellow-pigmented, Gram-negative rods with a single polar or subpolar flagellum. Growth temperature was between 30-55 ℃ (the optimal growth at 40-50 ℃). The isolates could grow in the medium containing NaCl up to 15 % (w/v). Both group II isolates and M. loti could proliferate in the nitrogen-free modified Thermus medium. The mol% G+C contents of the isolates were 61.7-62.4. Base on the DNA-DNA homology (3.0 -13.3 %), the 16S rRNA gene sequence analysis between the isolates and reference strain (95.27-95.49 %) as well as physiological, biochemical and chemical analyses indicated the isolates represented a novel member of the genus Mesorhizobium.