Genomic and Functional Insights Into Bacillus cereus SH-10 for Mitigating Lead Stress in Soybean.

Beneficial microbes serve as powerful biological tools for enhancing stress tolerance in crops. This study aimed to isolate stress-tolerant, plant growth-promoting bacterium, characterise it using high-throughput next-generation sequencing and expression profiling and assess its potential in improving soybean (Glycine max (L.) Merr.) growth and development under lead (Pb) stress. We identified Bacillus cereus SH-10 as a metal-resistant rhizobacterium capable of tolerating Pb concentrations exceeding 75 mg/kg. When inoculated into soybean plants under Pb stress, SH-10 significantly improved phosphorus and calcium uptake and reduced Pb accumulation. This reduction was associated with increased expression of the stress signalling protein GmCYP82A3. SH-10 also modulated the phytohormone balance by lowering abscisic acid (ABA) levels in shoots and enhancing salicylic acid (SA) biosynthesis. These hormonal shifts corresponded with the downregulation of ABA biosynthesis-related genes (GmNCED1, NCED3, GmbZIP) and the upregulation of the SA biosynthesis gene GmPAL1. Furthermore, SH-10 significantly mitigated oxidative stress in Pb-exposed plants, while enhancing antioxidant activities. The study also identified two phytohormone biosynthesis pathways in rhizobacteria: (1) Terpenes → β-carotene → Xanthoxin → ABA, and (2) Terpenes → Geranylgeranyl diphosphate → gibberellic acid. These findings highlight Bacillus cereus SH-10 as a promising biofertiliser that alleviates Pb toxicity in crops.