Isolation and characterization of multitrait Bacillus spp. that exhibit in vitro bioremediation of heavy metals and pesticides

This is the authors' abstract. We don't add key points for this paper.

Soil health and agricultural productivity are severely threatened by agrochemical pollution and heavy metal accumulation. This study aimed to isolate, characterize, and construct a multi-strain Bacillus spp. consortium possessing simultaneous plant growth-promoting rhizobacteria (PGPR) traits, heavy metal tolerance, and pesticide degradation capabilities to serve as a sustainable bioremediation tool. Spore-forming bacteria were isolated from 44 diverse Indian crop rhizosphere soil samples via enrichment and heat-shock treatment. Non-hemolytic isolates were screened for mineral solubilization, diazotrophic growth, and inter-strain compatibility. Formulated multi-strain blends were evaluated for heavy metal tolerance against HgCl2, Pb(CH3COO)2, NiCl2, and As2O3 and compatibility with six agrochemicals. Malathion biodegradation was tracked using plate assays and confirmed via liquid chromatography-tandem mass spectrometry (LC–MS/MS). Six distinct Bacillus strains (Bacillus amyloliquefaciens, Bacillus subtilis, Bacillus haynesii, Bacillus tequilensis, Bacillus licheniformis, and Bacillus halotolerans) were identified. These strains demonstrated specialized phosphate (up to 65.13 mg/L) and potash (up to 9.43 mg/L) solubilization. Excluding the antagonistic B. tequilensis, four consortia were developed. Blend 2 (B. amyloliquefaciens–B. subtilis–B. licheniformis) exhibited the highest heavy metal resilience, tolerating lead up to 1000 mg/L. Crucially, B. haynesii and B. licheniformis actively degraded the organophosphate malathion. LC–MS/MS verified biotransformation, mapping the metabolic breakdown into malathion monocarboxylic acid (MMC), and malathion dicarboxylic acid (MDC). This study presents the first official report of breakdown of malathion by B. haynesii. The developed multi-strain Bacillus consortia show promising functional advantages over single-strain inoculants, providing a highly effective, multifaceted strategy for sustainable agriculture and environmental bioremediation.