Physiological responses and heavy metal detoxification potential of soil bacteria from bioslurry and Lapindo mud

Abstract

Heavy metal pollution, especially lead (Pb) and chromium (Cr), poses an environmental problem that requires effective, sustainable remedial technologies. The objective of this study was to characterize the physiological responses and detoxification potential of bacterial isolates from bioslurry and Lapindo mud under Pb and Cr stress and to evaluate their potential as biostimulants. The isolates were morphologically, physiologically, and biochemically characterized and molecularly characterized using the 16S rRNA gene. Then they were evaluated for metal tolerance, Pb and Cr reduction capabilities in liquid media and soil, and detoxification efficiency through bioassays using Macrobrachium sp. The identification results showed that the bioslurry isolate was Paenibacillus polymyxa, and the Lapindo mud isolate was Lysinibacillus xylanilyticus. P. polymyxa showed better exopolysaccharide (EPS) production, phosphate solubilization, indole-3-acetic acid (IAA) synthesis, and nitrogen fixation capabilities, while L. xylanilyticus showed better biofilm formation capabilities. Both isolates were able to withstand metal stress. Bacterial inoculation reduced Pb and Cr residues in both liquid media and soil compared to controls; the highest reduction efficiency was achieved by a consortium of both isolates, 85.0% for Pb and 97.2% for Cr, lowering soil metal residues to 0.558 mg L-¹ (Pb) and 0.057 mg L-¹ (Cr). Detoxified water also supported the survival of Macrobrachium sp., in contrast to treatments without bacteria. These findings indicate that both isolates have the potential to be developed as bioremediation agents and biostimulants to support the restoration of heavy metal-contaminated soil and water bodies.