Bioremediation of Produced Water by a Polyextremophilic, Heavy-Metal-Resistant Modicisalibacter sp. Strain Wilcox

Produced water (PW), generated during oil and gas extraction, is a complex wastewater characterized by high salinity, hydrocarbons, and heavy metals, making treatment and beneficial reuse challenging. Bioremediation offers a sustainable treatment alternative, but the extreme physicochemical conditions of PW inhibit the growth and activity of most conventional microorganisms. This study evaluates the bioremediation potential and heavy metal tolerance mechanisms of the halophile, Modicisalibacter sp. strain Wilcox, isolated from PW. We examined its growth and benzene, toluene, ethylbenzene, and xylenes (BTEX) degradation capability under elevated salinity in defined media and raw PW, while assessing the effects and fate of metals individually and in multimetal mixtures. Strain Wilcox demonstrated exceptional tolerance to individual metals, including 100 mM arsenate, 100 mM manganese, 12.5 mM cadmium, and 7 mM zinc. Increasing metal concentrations and multimetal mixtures reduced BTEX degradation rates, with toxicity varying by metal species and salinity. In addition to hydrocarbon degradation, the strain removed 75-99% of Mn²⁺, Zn²⁺, Se⁴⁺, Pb²⁺, Cr³⁺, and Cu²⁺ via biosorption and bioaccumulation. Functional genomic analysis supported these phenotypes, revealing >70 metal resistance genes, 58 osmoregulation genes, and ∼70 genes associated with cross-protection against salt and metal stress, highlighting strain Wilcox's potential for bioremediation of PW.