Bacterial Potency Tests for Bioaugmentation in Post-Mining Land

Abstract

Revegetated post nickel mining soils in Pomalaa, Southeast Sulawesi, are characterized by low fertility and excessive concentrations of heavy metals, particularly nickel and chromium, which severely hinder plant growth and environmental sustainability. This study aimed to isolate and characterize indigenous bacterial strains capable of reducing nickel and chromium concentrations and enhancing soil fertility through key plant growth promoting traits. A total of 72 bacterial isolates were obtained from composite soil samples collected across southern, central, and northern post mining zones. Of these, 48 isolates demonstrated growth in media containing 10 ppm NiCl₂ and CrCl₂. Ten isolates with the highest biochemical potential were further evaluated for their ability to produce indole-3-acetic acid (IAA), gibberellic acid (GA₃), solubilize phosphate, fix atmospheric nitrogen, and reduce nickel and chromium concentrations. The most active strains included TT1cr-32 (IAA, 8.0 ppm), TU2cr-41 (GA₃, 2.99 ppm), TT1cr-33 (phosphate solubilization, 12.53 ppm), and TT1ni-32 (nitrogen fixation, 1292.99 ppm). Nickel reduction was most effective in isolate TU3ni-41, achieving 97.29% and 95.55% reduction at 300 ppm and 700 ppm nickel respectively, while TS1cr-5 exhibited the highest chromium reduction (65.62% at 300 ppm and 48.27% at 700 ppm chromium. Based on Bergey's Manual, the dominant genera were Clostridium and Bacillus, both of which are known for their heavy metal resistance and soil enhancing properties. These findings suggest that native bacteria from post mining soils can serve as promising agents for bioaugmentation, offering an integrated solution for both heavy metal remediation and ecological restoration of degraded land.