六株耐酸苜蓿根瘤菌的筛选及生长特性研究

为获得能够使紫花苜蓿在酸性土壤中高效结瘤的耐酸根瘤菌，该研究从酸性土（pH5.2）上生长的紫花苜蓿根瘤中分离到若干菌株，利用根瘤菌对酸的适应性耐受反应筛选到六株能够在pH4.8的固体培养基上稳定生长的菌株，并检测了这六株菌的结瘤特征、不同酸度下的生长曲线和平均代时。结果表明，六株根瘤菌均能使紫花苜蓿植株结瘤，使其具有较多的结瘤数（≥10个/株）和较高的结瘤率（66.67%~100%）；不同酸度下，六株根瘤菌呈现不同的生长特性，酸显著降低根瘤菌的生长速率，使其生长延滞期增长，对数生长期出现滞后，稳定期到达延迟，酸性条件下各根瘤菌的平均代时均较中性条件下的长，环境pH越低，菌株平均代时越长。然而，在低pH条件下，耐酸根瘤菌在其耐受酸度范围内经过延长的延滞期后仍然能够较快地生长

Isolation of Six Acid-tolerant Rhizobium meliloti and Study on its Growth Characteristics

In order to discover acid-tolerant Rhizobium meliloti that can nodulate alfalfa high-effectively on acidic soil, researches were explored to isolate rhizobia from alfalfa nodules on acidic soil (pH5.2), methods based on the thesis of adaptive acid-tolerance response of the Rhizobia were adopted, six strains were isolated, which could grow on solid medium with pH4.8 steadily. In addition, the nodulation characteristics, growth curves and mean generation time under different acidity of the strains were examined. The results showed that all the rhizobia could nodulate alfalfa with enough nodules (≥10) and high nodulation ratio (about 66.67%~100%); under different acidity, the rhizobia represented different growth characteristics, acid slowed strains’ growth rate significantly, which made the rhizobia exhibit a prolonged lag phase, a lagged log phase and a delayed stationary phase, the mean generation time under acidic condition was longer than that under neutral condition, the lower the pH was, much longer the mean generation time was. However, the acid-tolerant rhizobia, if exposed to the tolerant acidity range, could still grow quickly after a prolonged lag phase