Taxonomic Characteristics of Nitrogen-Fixing Oligotrophic Bacteria from Forest Soil

산림토양으로부터 분리한 저영양성-질소고정세균의 분류학적 특성

  • 황경숙 (목원대학교 생명과학부 미생물학과)
  • Published : 2001.06.01

Abstract

Many isolates from different forest soil layers did not show appreciable growth on full strength of the conventional nutrient broth (NB medium) but grow on its 100-fold dilution (DNB medium). These isolates were divided into four types according to organic nutrient concentration in the growth medium from $1^{-1}\;to\;10^{-4}$dilution of normal NB medium. Oligotrophic bacteria were type II and type IV which grew in $10^{-4}$ dilution of NB (1 mg C/l) medium. Sixty strains were isolated for obligate oligotrophic bacteria. Chemotaxonomic and phylogenetic characteristics of eleven isolates of acetylene-reducing (nitrogen-fixing) oligotrophic bacteria from forest soil were investigated. They showed similar characteristics: the cellular fatty acid mainly consisted of straight-chain unsaturated $C_{18:1}$ (60-84% of total fatty acids). Ubiquinone Q-10 and a high guanine plus-cytosine content(61-64 mol%) were found. Eleven isolates of nitrogen-fixing oligotrophic bacteria were found to be closely related by full 16S rDNA sequence simility and many common taxonomic traits. Analysis of full 16S rDNA sequences of eleven isolates indicated that they were more closely related to Bradyrhizobium (similarity values: 98.1-98.8%), Agromonas, Nitrobacter, and Afipia.

산림토양의 각 토양층으로부터 분리된 세균 중에는 통상 농도의 NB배지에서는 중식이 현저히 저해되고 희석한 DNB 배지에서만 중식이 가능한 세균이 다수 포 되어 있었으며, 이들 세균은 NB배지를 $10^{-1}$~$10^{-4}$배로 희석한 배지에서의 증식양상에 따라 4가지형으로 구분되었다. 본 연구에서는 저영양세균의 기준에 따라 $10^{-4}$NB(1 mg C/liter)배지에서 양호하게 증식하는 Type II와 IV세균을 저영양세균으로 분류하였고, 60개의 Type IV(편성저영양세균; obligate oligotrophic bacteria)균주를 순수분리 하였다. 이들 저영양성 세균중 질소고정능을 갖는 11균주에 대하여 화학분류 및 계통분류학적 특성을 검토한 결과 모든 균주는 주요 균체지방산으로 $C_{18:1}$)을, 퀴논종은 Q-10을 함유하였으며, G+C함량은 61-64 mol%범위를 나타내었다. 16S rDNA염기서열을 결정한 결과 각 균주는 Proteobacteria $\alpha$-subdivision의 BANA domain (Bradyrhizobium, Agromonas, Nitrobacter 및 Afipia)에 속하였고 Bradyrhizobium japonicum 및 Bradyrhizobium elkanii와 98% 이상의 높은 상동성을 나타내었다. 나타내었다.

Keywords

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