Introduction/Background: Acidic soils are limiting the production of crops and indirectly harming the
environment due to the use of nitrogen (N) chemical fertilizer. Therefore, the current study aims to
isolate a promising N2-fixing candidate to solve this issue in some communes of Phu Luong District, Thai
Nguyen Province, Vietnam.
Materials and Methods: The bacteria were isolated using the Ashby medium. The IAA generation and
nitrogen fixation were assessed using spectroscopy. The selected bacteria were tested at temperatures
ranging from 28°C to 42°C and pH levels of 4.0 to 9.0. As a result, the Box-Behnken model yielded a
growth equation. The API kit test was used to measure the biochemical properties of the selected
bacteria.
Results: The result demonstrated that there were ten nitrogen-fixing bacteria (NFB) isolates with
capacities of N2 fixation and IAA production at 2.35–24.61 and 0.00–119.13 μg/ml. Among them, the NL3
strain was the best strain. The optimum condition to grow the NL3 strain was calculated as 5.44 days at
pH 7.10 and temperature of 32.18°C to reach a bacterial density of 9.77929×108 CFU/ml. In addition,
the NL3 strain was identified as an Azotobacter species. The genomic analysis revealed that the genome
of Azotobacter sp. NL3 was nearly 5.4 Mb long and contained 45 N2 fixation-relating genes and 7 IAA
production-relating genes.
Conclusion: Not only can this study provide insight into the features of Azotobacter spp., but it also
introduces a potent candidate that can improve soil health and crop yield by fixing N2 and producing IAA
in order to limit the use of N chemical fertilizer for a sustainable agriculture. Therefore, the selected
bacterial strain should be further tested under the local field conditions and subsequently
commercialized as a biofertilizer.