Lead Bioremoval by Halotolerant Bacteria Isolated from Mangrove Rhizosphere Soils of Saudi Arabia

Bioremediation of hypersaline environments contaminated with heavy metals is challenging due to high salinity levels, particularly when using conventional microorganisms. This study aimed to isolate and identify halotolerant and halophilic bacteria from various mangrove rhizosphere soil samples in Saudi Arabia and to evaluate their ability to remove heavy metals under high-salinity conditions. Out of 27 isolated strains, LD57 and LR40 demonstrated the highest resistance to lead ions. Both isolates grew well at 37 °C in the presence of 3 M NaCl and recorded growth at varying concentrations of lead nitrate, ranging from 100 to 4500 ppm. The lead’s minimum inhibitory concentrations (MICs) were determined to be 3500 ppm for isolate LD57 and 4500 ppm for isolate LR40. Analysis of 16S rRNA sequences of the two isolates LD57 and LR40 revealed that they were identified as Halomonas salina strain LD57 (accession number PP767765) and Vreelandella alkaliphila strain LD40 (accession number PP767765.1). The study also investigated the effects of various factors on the growth of both isolates when exposed to 700 ppm lead. The optimal growth occurred at pH 8.0, 35 °C, over 2 to 3 days. The biosorption capacities for lead were found to be 99.89% for isolate LD57 and 99.44% for isolate LR40 using dry live biomass. In conclusion, lead bioremediation in hypersaline environments can be effectively achieved using lead resistance H. salina and V. alkaliphila.