Adaptive acclimatization yields a Bacillus velezensis strain with enhanced nitrate metabolism for remediating salinized soil

Abstract

Microbial inoculants show potential for remediating nitrate-rich, salinized soils. However, native strains often exhibit suboptimal performance under high-salinity and high-nitrate conditions, limiting their practical application. To develop a nitrate-reducing strain suitable for saline soil remediation, we adaptively acclimated a nitrate-reducing Bacillus velezensis strain BV-1 under high-nitrate conditions to enhance its salt tolerance and nitrogen metabolic capacity. The acclimatized strain exhibited significantly upregulated nar genes (4.71- to 7.56-fold) and nirD expression (1.36-fold), indicating enhanced nitrate assimilation and dissimilatory nitrate reduction to ammonium activity. In pot experiments, inoculation with this strain resulted in 46.85% nitrate removal, improved nutrient utilization (with increases of 21.86% in ammonium-N and 29.64% in available phosphorus utilization), and a 20.82% increase in lettuce fresh weight. These findings demonstrate that microbial acclimatization is an effective strategy for developing robust bioinoculants, with broad implications for sustainable agriculture and microbial strain engineering in salinized environments.