Echigo Akinobu, Hino Miki, Fukushima Tadamasa, Mizuki Toru, Kamekura Masahiro, Usami Ron
Department of Applied Chemistry, Faculty of Engineering, Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-8585, Japan.
Saline Syst. 2005 Oct 20;1:8. doi: 10.1186/1746-1448-1-8.
Generally, extremophiles have been deemed to survive in the extreme environments to which they had adapted to grow. Recently many extremophiles have been isolated from places where they are not expected to grow. Alkaliphilic microorganisms have been isolated from acidic soil samples with pH 4.0, and thermophiles have been isolated from samples of low temperature. Numerous moderately halophilic microorganisms, defined as those that grow optimally in media containing 0.5-2.5 Molar (3-15%) NaCl, and halotolerant microorganisms that are able to grow in media without added NaCl and in the presence of high NaCl have been isolated from saline environments such as salterns, salt lakes and sea sands. It has tacitly been believed that habitats of halophiles able to grow in media containing more than 20% (3.4 M) are restricted to saline environments, and no reports have been published on the isolation of halophiles from ordinary garden soil samples.
We demonstrated that many halophilic bacteria that are able to grow in the presence of 20% NaCl are inhabiting in non-saline environments such as ordinary garden soils, yards, fields and roadways in an area surrounding Tokyo, Japan. Analyses of partial 16S rRNA gene sequences of 176 isolates suggested that they were halophiles belonging to genera of the family Bacillaceae, Bacillus (11 isolates), Filobacillus (19 isolates), Gracilibacillus (6 isolates), Halobacillus (102 isolates), Lentibacillus (1 isolate), Paraliobacillus (5 isolates) and Virgibacillus (17 isolates). Sequences of 15 isolates showed similarities less than 92%, suggesting that they may represent novel taxa within the family Bacillaceae.
The numbers of total bacteria of inland soil samples were in a range from 1.4 x 10(7)/g to 1.1 x 10(6)/g. One tenth of the total bacteria was occupied by endospore-forming bacteria. Only very few of the endospore-forming bacteria, roughly 1 out of 20,000, are halophilic bacteria. Most of the halophilic bacteria were surviving as endospores in the soil samples, in a range of less than 1 to about 500/g soil. Samples collected from seashore in a city confronting Tokyo Bay gave the total numbers of bacteria and endospores roughly 1000 time smaller than those of inland soil samples. Numbers of halophilic bacteria per gram, however, were almost the same as those of inland soil samples. A possible source of the halophilic endospore originating from Asian dust storms is discussed.
一般来说，嗜极微生物被认为能在它们所适应生长的极端环境中存活。最近，许多嗜极微生物已从预期它们无法生长的地方分离出来。嗜碱微生物已从pH值为4.0的酸性土壤样本中分离出来，嗜热微生物已从低温样本中分离出来。许多中度嗜盐微生物（定义为在含有0.5 - 2.5摩尔（3 - 15%）氯化钠的培养基中生长最佳的微生物）以及能够在不添加氯化钠和存在高浓度氯化钠的培养基中生长的耐盐微生物已从盐田、盐湖和海沙等盐环境中分离出来。一直以来人们默认，能够在含有超过20%（3.4摩尔）氯化钠的培养基中生长的嗜盐微生物的栖息地仅限于盐环境，且尚未有关于从普通花园土壤样本中分离嗜盐微生物的报道。
我们证明，许多能够在20%氯化钠存在的情况下生长的嗜盐细菌存在于日本东京周边地区的非盐环境中，如普通花园土壤、庭院、田地和道路。对176株分离菌的部分16S rRNA基因序列分析表明，它们是嗜盐细菌，属于芽孢杆菌科的芽孢杆菌属（11株分离菌）、丝状芽孢杆菌属（19株分离菌）、纤细芽孢杆菌属（6株分离菌）、嗜盐芽孢杆菌属（102株分离菌）、缓长芽孢杆菌属（1株分离菌）、副芽孢杆菌属（5株分离菌）和 Virgibacillus属（17株分离菌）。15株分离菌的序列显示相似度低于92%，这表明它们可能代表芽孢杆菌科内的新分类单元。
内陆土壤样本中的细菌总数在1.4×10⁷/g至1.1×10⁶/g范围内。形成芽孢的细菌占细菌总数的十分之一。形成芽孢的细菌中只有极少数（大约每20000个中有1个）是嗜盐细菌。大多数嗜盐细菌以芽孢形式存在于土壤样本中，每克土壤中的数量在不到1个至约500个的范围内。从东京湾对面城市的海岸采集的样本中，细菌和芽孢的总数比内陆土壤样本大约少1000倍。然而，每克土壤中嗜盐细菌的数量与内陆土壤样本几乎相同。本文讨论了源自亚洲沙尘暴的嗜盐芽孢的可能来源。
