Evaluating the potential application of Azospirillum isscasi with nitrogen-fixing and indole-3-acetic acid-producing activities isolated from rice paddy soil in Thai Nguyen Province

Abstract

This study aimed to select indigenous bacterial strains with high nitrogen-fixing and indole-3-acetic acid (IAA) producing capacities from paddy soils collected in several mountainous communes of Thai Nguyen province. From 45 soil samples, 16 promising bacterial strains were isolated. Three strains with superior nitrogen fixation and IAA production were initially selected. Among these, strain NL2026 being the best, demonstrated by its enhanced efficacy on rice plants after 7 days of sowing. This strain exhibited an ammonium accumulation capacity of (76.7 µg/ml) and IAA production (176.85 µg/ml), and enhanced root length and shoot length of rice plants by 50 and 17.41%, respectively, compared to the control. The 16S rRNA gene sequence of strain NL2026, compared to standard strains on EzBioCloud, shows a 98.94% similarity to Azospirillum isscasi C340-1^T, belonging to the same phylogenetic tree as Azospirillum isscasi C340-1^T, named as Azospirillum isscasi NL2026. Cultivation of NL2026 in Ashby medium at 35°C, pH 6.5, with a shaking speed of 150 rpm resulted in optimal growth (reaching a maximum density of 8.94 log₁₀ CFU/ml). Given its demonstrated bioactivities, strain NL2026 shows considerable potential for application in the development of biofertiliser products, contributing to the advancement of green and sustainable agriculture.