Objective To study the growth characteristics of functional strains and to explore the principles of suitable bacteria.

Method In this study, the effects of 10 pH gradients and 8 temperature gradients on the growth of 103 strains of nitrogen-fixing bacteria were researched.

Result There were 103 bacterial strains containing nifH gene. The most suitable growth conditions of these strains were 28℃, pH=7. The temperature ranges suitable for growth were 20, 28 and 37℃, the pH values were 4, 5, 7 and 8. The strain 6003 was suitable to grow in low temperature alkaline soil, while the strains 09ul27, 1010, 2024, 029, 7002, lk2-1c (2) and zk3-1 were suitable to grow in high temperature alkaline soil. The strains suitable for growth in acid and alkaline soils were 1012 and 2025. According to the different growth characteristics of the bacteria, all the strains were classified into 9 categories by using SSI algorithm. Both the fifth and seventh categories belonged to Burkholderia, the second category belonged to Bacillus. There was no obvious clustering phenomenon in the other categories, and there was no significant correlation between the growth condition classification and the strains identification.

Conclusion The suitable growth environment of the nitrogen-fixing bacteria is similar, and the most suitable growth conditions of these strains are 28℃, pH=7. 10 strains of nitrogen-fixing bacteria suitable in special environment are screened out. These strains are initially identified as Bacillus subtilis subsp, Bacillus cereus, Bacillus megaterium, Chitinophaga pinensis, Burkholderia xenovorans, Burkholderia phymatum, and Burkholderia bannensis. The results also show that the growth characteristics of the strains are not completely correlated with their biological characteristics by growth condition cluster analysis and 16S rDNA identification.