Red pigment from isolated Serratia marcescens SEM: Structure, antimicrobial and antioxidant activity

Abstract

Pigments from microbial sources are likely to be suitable alternatives to synthetic pigments. Not only do natural pigments have the potential to increase product marketability, but they also exhibit valuable biological activities as antioxidants and antimicrobial agents. Recently, microbial prodigiosin (PG) has received a lot of attention due to its many beneficial applications. PG is a natural red dye. It is an alkaloid secondary metabolite with a unique tertiary structure produced by Serratia marcescens. The purpose of our study was to isolate indigenous strains of S. marcescens and identify it, extraction the red pigment from culturable bacteria to confirm its structure, evaluate its antimicrobial activity against a series of pathogenic microbes (Staphylococcus aureus NRRL B-313 and Bacillus subtilus NRC, Escherichia coli NRC B-3703, Pseudomonas aeruginosa NRC B-32, Candida albicans ATCC1023 and Aspergillus niger NRC) by well diffusion assay and antioxidant activities by DPPH assay. The isolate was identified by morphological characteristics and 16S rRNA sequencing as S. marcescens SEM, with accession number OM757735.1. PG from S. marcescens was first confirmed its purity by UV absorption spectrum, FTIR and GC-MS spectrophotometer. PG possess effective antimicrobial activity against tested pathogens, with MIC 1.0 ± 0.15, 5.0 ± 0.25, 16.5 ± 0.87, 16.5 ± 0.92 and 3.3 ± 0.17 μg/mL against B. cereus, St. aureus, E. coli, P. aurgenosa, and C. albicans, respectively. Also, PG possess highly antioxidant activity 97.2% at the concentration of 400 μg/ml after 120 min in dark, this activity increased gradually with increasing concentrations and time of incubation in dark,with IC50 (250 μg/ml at 30 min; 225 μg/ml at 60 min; 200 μg/ml at 90 min; 125 μg/ml at 120 min).