Five endophytic diazotrophs with high and stable nitrogenase activity screened from Guangdong bamboo(Bambusa blumeana J.A.et J.H.Schult.f.)were studied by physiological test,the adaptability to environments and the growth-promoting effects on rice.The results showed that these strains could grow well at 18—40 ℃and had nitrogenase activity at 26—37 ℃for optimum growth under nitrogen-free medium.Strains also showed nitrogenase activity at a pH range of 5.0 to 8.0,at a saline(NaCl) concentration range of 0.5—2.5 g·L-1and at a range of 0.05—0.50 g·L-1(NH_4)_2SO_4.Strains can secrete acid or alkali substance as neutralizer at pH 8.0 and 5.0 respectively.Experiments of inoculation on rice showed that strains had obviously effects on promoting the growth of plants.

AbstractEndophytic bacteria isolated from Guangdong bamboo (Bambusa blumeana) plants were obtained under aerobic and anaerobic cultural conditions. Using the acetylene reduction assay (ARA), 40 strains were identified as diazotrophs. Diazotrophic isolates were grouped into five clusters (I, II, III, IV and V) by SDS-PAGE whole-cell protein patterns. The analysis of full-length 16S rDNA sequences of the representative strains of each group indicated that the endophytic diazotrophs showed great diversity and belonged to the generaAzospirillum(α-subclass of proteobacteria),EscherichiaandPseudomonas(γ-subclass of proteobacteria), andAquaspirillum(β-subclass of proteobacteria).

糖蜜草(Melinis minutiflora Beauv.)是热带地区的一种优良牧草.采用选择性培养基在厌氧和好氧两种培养条件下,从糖蜜草根、茎中都可分离得到具有较强固氮酶活性的菌株.通过SDS-PAGE全细胞蛋白电泳技术快速聚类分析表明,来源于糖蜜草中的菌株为同一类群.16S rDNA序列分析和总DNA的G+C%含量进一步确定糖蜜草中所分离的菌株属于固氮螺菌属(Azospirillum),与产脂固氮螺菌(Azospirillum lipoferum) 亲缘关系较近.BIOLOG 板测定结果显示,糖蜜草菌株TMCY243 对多种碳源具有很强的适应性, 与产脂固氮螺菌(A. lipoferum)的模式菌株DSM 1691存在着较大的差异.以上结果表明,糖蜜草内生固氮菌为固氮螺菌属的一个新类群.

Fifteen bacterial strains isolated from molasses grass (Melinis minutiflora Beauv.) were identified as nitrogen-fixers by using the acetylene-reduction assay and PCR amplification of nifH gene fragments. These strains were classified as a unique group by insertion sequence-PCR fingerprinting, SDS-PAGE protein patterns, DNA-DNA hybridization, 16S rRNA gene sequencing and morphological characterization. Phylogenetic analysis of the 16S rRNA gene indicated that these diazotrophic strains belonged to the genus Azospirillum and were closely related to Azospirillum lipoferum (with 97(.)5% similarity). In all the analyses, including in addition phenotypic characterization using Biolog MicroPlates and comparison of cellular fatty acids, this novel group was found to be different from the most closely related species, Azospirillum lipoferum. Based on these data, a novel species, Azospirillum melinis sp. nov., is proposed for these endophytic diazotrophs of M. minutiflora, with TMCY 0552(T) (= CCBAU 5106001(T) = LMG 23364(T) =CGMCC 1.5340(T)) as the type strain.

Endophytic diazotrophs isolated from molassess grass, Melinis minutiflora,were studied by insert sequence(IS)-PCR fingerprinting patterns and full length of 16S rRNA gene sequences.IS-PCR fingerprinting showed that different patterns appeared between isolates and the type strain DSM 1691 of Azospirillum lipoferum;16S rRNA gene sequence analyses indicated that homology between isolates and known species Azospirillum lipoferum is 97%. These results suggested that isolates from molasses grass are possible a new group of endophytic diazotrophs closely related to Azospirillum lipoferum.