Radical scavengering of pigments from novel strains of Dietzia schimae and Microbacterium esteraromaticum

Radiation resistant bacteria have adopted a variety of ingenious strategies for survival under the high dose of radiation, for example through their pigments. In the present study, two ultraviolet-C (UVC) radiation tolerant bacteria, named NM1 and NM3 strains, were isolated from the industrial waste and soil that identified by the molecular analysis. Survival assay of irradiated bacteria was performed by plate counting and flow cytometry (by a fluorescent dye, Rhodamin 123). Also, hydrogen peroxide tolerance of the isolated strains was analyzed by turbidimetric microplate technique. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and EC₅₀ values in reducing power were measured to evaluate antioxidant activity and reductive power of their methanol extracted pigments. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that the NM1 and NM3 strains belonged to Microbacterium esteraromaticum and Dietzia schimae with 99% identity, respectively. Both of them showed much high resistance to 15 and 20 J/cm² UVC irradiation (254_nm). Visible spectra of their methanolic extracted pigments were considered identical with λ_max at 413, 439 and 468_nm for Microbacterium NM1 and λ_max at 451_nm for Dietzia NM3. EC₅₀ values in reducing power were 35.26 and 36.13 µg/ml for pigments of NM1 and NM3 strains, respectively. Whereas scavenging abilities of DPPH radicals were 3.42 and 1.58 mg/ml for pigments of NM1 and NM3 strains, respectively. Based on the results, the pigments of isolated UVC tolerant bacteria displayed strong antioxidant activity. These bacteria may be a good source for antioxidative-related functional foods and the pharmaceutical industry.