Introduction: Some Azotobacter species can produce melanin. Melanin protects against UV. The purpose of this study was to isolate Azotobacter with the power of producing melanin and optimize its production and the effect of its combination with titanium oxide nanoparticles on the protection against ultraviolet light (UV).
 
Materials & Methods: Overall, 200 soil samples from different parts of Qom, Iran, were cultured on Ashby's mannitol agar medium using Bio-test method. The effect of optimization of conditions such as pH, temperature, glucose source, amino acid sources, and aeration on the amount of melanin production was assessed. Afterwards, melanin was extracted, conjugated with titanium nanosilicate compound, and then the effect of each of the compounds on Escherichia coli was examined under the influence of UV based on time.
 
Findings: Melanin-producing Azotobacter vinelandii species were isolated. The optimum pH was determined about 7.5. Glucose at different concentrations (1-6%) reduced the production of the product. Methionine amino acid had an inhibitory effect, while tyrosine amino acid increased the production rate. Tryptophan amino acid at 0.1-0.7% also increased the production rate, while cysteine and phenylalanine did not change the production rate. The combination of titanium oxide with melanin showed a significant protective effect against Escherichia coli bacterium under the influence of UV.
 
Discussion & Conclusions: Native isolates of Azotobacter isolated from agricultural soil with the power of producing melanin can be used as a source for its use in the industry.