Characterization and activity of endophytic bacteria from ‘Prata Anã’ banana crop (Musa sp., AAB)

ABSTRACT The objective of this study was to characterize banana tree endophytic bacteria at genus and species level and to determine the metabolic reactions associated with the nitrogen transformations. The identification at genus and species levels was performed using the partial sequencing of the rDNA 16S region. The assimbyotic nitrogen fixation, the reduction of nitrate and the production of urease were in vitro evaluated. The DNA of the bacterial isolates was also amplified to verify the presence of the nifH, nirK and nirS regions. Biochemical tests were performed in a complete randomized design; the treatments consisted of 39 bacterial isolates with three replications. Sequence analysis enabled the identification of four genera: Bacillus, Rhizobium, Klebsiella and Enterobacter. The Bacillus genus occurred more frequently, nine species were identified. By evaluating the results of biochemical tests, it was observed that three isolates showed multiple abilities: growth in NFb medium, nitrate reduction and production of urease. The isolates belong to the genus Bacillus and of the species subtilis, thuringienses and amyloliquefaciens. Approximately 12.5% of the isolates amplified the region corresponding to the nifH gene, 7.5% amplified gene nirK and 3.9% amplified the nirS gene. Endophytic bacteria evaluated in the present study showed in vitro activity for urease, nitrate reductase enzymes, however, relevant nitrogenase activity was not observed.

摘要
本研究旨在从属和种水平对香蕉树内生细菌进行分类鉴定，并明确其与氮转化相关的代谢反应。
本研究采用16S rDNA区域部分测序法完成属、种水平的鉴定，体外评估了非共生固氮、硝酸盐还原及脲酶产生能力；同时对细菌分离株的DNA进行扩增，以验证nifH、nirK及nirS基因区域的存在。
生化试验采用完全随机设计开展，处理组包含39株细菌分离株，设置3次生物学重复。
序列分析共鉴定出4个菌属：芽孢杆菌属（Bacillus）、根瘤菌属（Rhizobium）、克雷伯菌属（Klebsiella）及肠杆菌属（Enterobacter），其中芽孢杆菌属出现频率最高，共鉴定得到9个菌种。
通过生化试验结果分析可知，3株分离株具备多重代谢功能：可在NFb培养基中生长、还原硝酸盐并产生脲酶。该3株分离株均隶属于芽孢杆菌属，具体菌种分别为枯草芽孢杆菌（Bacillus subtilis）、苏云金芽孢杆菌（Bacillus thuringiensis）和解淀粉芽孢杆菌（Bacillus amyloliquefaciens）。
约12.5%的分离株扩增出了对应nifH基因的序列区域，7.5%的分离株扩增出nirK基因片段，3.9%的分离株扩增出nirS基因片段。
本研究所评估的内生细菌在体外可检测到脲酶、硝酸还原酶活性，但未观察到显著的固氮酶活性。