Improvement of nitrogen-fixing ability and survivability of nitrogen fixers in the rhizoshere of rice.

为获得在水稻根际具有较高存活力的固氮菌，采用无氮培养基从禾本科植物根系和根际土壤中分离固氮菌。4株革兰氏阴性兼性厌氧细菌中，经API 20试验鉴定3株为肺炎克雷伯菌。其中一株菌株（E-1030）经鉴定为泛菌属（Pantoea sp.），该菌株具有广谱抗菌活性，但在培养保存过程中失去了抗菌活性。分离到2株运动、产芽孢、兼性厌氧细菌，经生理生化和16 S rDNA序列分析，鉴定为类芽孢杆菌属（Paenibacillus sp.）。由于序列同源性为96 ~ 97%，故判定为新种，命名为藤类芽孢杆菌新种Br 1（DDBJ Accesion No.AB092351，Taxonomy ID 208550）和阿贝川类芽孢杆菌属（Paenibacillus abekawaensis sp. nov.MG1（DDBJ Accession No.AB119649，Taxonomy ID 244733），其固氮能力是克雷伯氏菌、固氮菌和草螺菌的7 ~ 15倍。在无氮培养基上接种水稻植株，结果表明，菌株Br 1对水稻植株的生长促进作用强于肺炎克雷伯氏菌M5 a1和固氮菌COC 8。

To obtain nitrogen-fixing bacteria with a high survivability in the rhizosphere of rice, bacteria were isolated from roots and rhizosphere soils of graminaceous plants, using N-free media. Among 4 Gram-negative facultatively anaerobic bacterial strains, 3 strains were identified as Klebsiella pneumoniae by API20 test. One strain (E-1030)was judged to be Pantoea sp. Strain E1030 had a broad spectrum antibiotic activity, but the activity was lost during culture preservation. Two motile, spore-forming and facultatively anaerobic bacterial strains were isolated, and they were identified to be Paenibacillus sp. by physiological properties and 16S rDNA sequence. As the sequence homologies were 96〜97% to the nearest Paenibacillus species, they were judged to be new species, and named Paenibacillus fujiensis sp. nov. Br1 (DDBJ Accesion No.AB092351, Taxonomy ID 208550), and Paenibacillus abekawaensis sp. nov. MG1 (DDBJ Accession No.AB119649, Taxonomy ID 244733), respectively.Nitrogen-fixing ability of P. fujiensis Br1 was 7〜15 times as large as those of commonly used Klebsiella, Azospirillum and Herbaspirillum strains. Inoculation test to rice plant aseptically cultured on an N-free medium in a glass cylinder showed that strain Br1 had greater growth promoting effects than Klebsiella pneumoniae M5a1 and Azospirillum lipoferum COC8, in terms of length and/or dry weight.