糖蜜草(Melinis minutiflora Beauv.)内生固氮菌分离鉴定

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。

Characterization of endophytic diazotrophs isolated from molasses grass

Molasses grass (Melinis minutiflora Beauv.) is a good fodder in tropical area. In this study, endophytic bacteria with high nitrogenase activity were isolated from the roots and stems of molasses grass grown in Guangdong province by using a selective medium under anaerobic or aerobic conditions. SDS-PAGE of whole-cell proteins clustered all the 15 isolates into a single group. 16S rDNA sequence analysis showed that these isolates belonged to the genus Azospirillum, and were closely related to A. lipoferum. BIOLOG test indicated that the representative strain, TMCY243, from molasses grass was able to utilize a wider range of carbon sources than the type strain DSM 1691 of A. lipoferum. Based on these results, we concluded that the endophytic diazotrophs isolated from molasses grass represented a new species of Azospirillum. This bacterium distributed widely in association with its host plant in the subtropic regions of China.