Bio-characterization of food grade pyocyanin bio-pigment extracted from chromogenic Pseudomonas species found in Pakistani native flora

Abstract

The consumer sensitivity toward application of synthetic colors led to exploitation of food grade bio-colors from bacteria. Pseudomonas aeruginosa is an opportunistic, gram-negative bacteria that secrete a variety of redox-active phenazine pigmented compounds, which are significant for a variety of biological activities. Pyocyanin, a water soluble blue green phenazine pigment producing P. aeruginosa was screened from aquatic habitats of isolation of Pakistan, identified and compared by 16S rRNA gene sequence for genetic variability. The similarity of selected strain was found 99% with P. aeruginoas DSM 50071 with accession no CP012001.1 in gene bank. Pyocyanin from the identified strain was extracted after 72 h of incubation by chloroform and purified with 0.1 N HCl and 1 N NaOH. Protective effects of the extracted pyocyanin as food colorant were evaluated against multiple biological activities. Pyocyanin showed anti-oxidant potential with 58.0% inhibition of 2,2-diphenyl-1-picrylhydrazyl radical compare to Trolox (68.5%) and BHT (88.1%) and 52.5% free radical scavenging of 2,2′-azinobis-(3-ethylbenzothiazoline-6- sulfonic acid) in comparison to Trolox (67.4%) and BHA (86.0%) at 50 μg/ml concentration. The anti-microbial efficacy of pyocyanin was assessed against food borne pathogenic bacteria and fungi by agar well diffusion method. Pyocyanin exhibited anti-bacterial activity with distinct zone of inhibition against B. spizizenii (16 mm), S. aureus (19 mm), E. aerogenes (14 mm), S. enterica (13 mm), P. aeruginosa (13 mm) and E. coli (12 mm) at 50 μg/ml concentration. Pyocyanin was more susceptible at the same concentration against fungal strains with zone of inhibition measuring 21 mm, 18 mm and 17 mm for F. oxysporum, A. niger and A. fumigatus respectively. Anti-biofilm profile of pyocyanin exhibited significant inhibition of the biofilm formation against biofilm forming bacteria B. cereus (81%), S. aureus (80%), P. aeruginonsa (78%) and K. pneumonia (76%) when assessed by crystal violet assay at 50 μg/ml concentration. Similar effects at the same concentration were observed in disruption of pre-formed biofilm against B. cereus (77%), S. aureus (76%), P. aeruginonsa (74%) and K. pneumonia (73%). The presented remarkable biological activities of pyocyanin against food borne pathogens augment the utilization of chromogenic microbes existing in Pakistani aquatic resource as an alternative potent source for efficient production of natural pigment and their application as natural color and bio-preservative in food industries.