Sustainable Arsenic Bioremediation by a Marine Macroalgal Endophyte, Bacillus subtilis ULB16

Arsenic contamination, particularly in the form of the highly toxic and mobile Arsenite (As (III)), poses a serious threat to environmental sustainability, agricultural productivity, and food safety. Biological detoxification using naturally resilient microorganisms offers a sustainable alternative to conventional remediation approaches. In this study, a marine macroalgal endophyte, Bacillus subtilis ULB16, isolated from Ulva lactuca , was evaluated for its As (III) tolerance, detoxification potential, and genetic basis of arsenic resistance. The strain exhibited a minimum inhibitory concentration (MIC) of 12mg/mL for As (III) and maintained growth over a broad pH range (4-11) and temperatures between 28 and 45°C. As (III) exposure induced changes in colony morphology, cell surface ultrastructure, and cell envelope-associated functional groups, indicating adaptive responses to arsenic stress. ICP-MS analysis demonstrated that approximately 80% of the arsenic was removed from the culture medium within 48 h, with negligible intracellular arsenic accumulation, while a qualitative silver nitrate assay confirmed the oxidation of As (III) to As (V) In a hydroponic system, bacterial treatment alleviated As (III)-induced phytotoxicity in Vigna radiata , with pre-treatment of the As (III)-containing medium resulting in greater plant growth recovery and minimal arsenic accumulation in plant tissues compared with direct inoculation. Whole-genome sequencing identified multiple arsenic resistance-associated genes, including arsR, arsB, arsC, czrA , and cotA , providing a molecular basis for the observed arsenic tolerance. Collectively, the physiological, analytical, and genomic findings demonstrate that B. subtilis ULB16 possesses multiple arsenic resistance traits and highlight its potential as a promising candidate for biological arsenic bioremediation.