Cyanobacteria possess a wide array of bioactive compounds including those with antimicrobial activities. The target was to investigate the UV effect on antimicrobial activity of cyanobacterial extracts. Several cyanobacterial strains were isolated from Eastern region of KSA as well as three plant pathogenic bacterial strains. Four cyanobacterial strains were used. Two strains were isolated from Al Uquair region, Arabian Gulf, and identified as Synechococcus sp. and Oscillatoria sp. The two other strains were collected from brackish stream of underground water and were characterized as Synechocystis sp. and Phormidium sp. The antimicrobial bioassay was then performed using cyanobacterial aqueous extracts. The antimicrobial effect was estimated by measuring the inhibition zone compared to that of control. The extract was divided into 2 parts: part was not exposed to UV and the other was exposed to UV-B irradiation for 10 min. The antimicrobial bioassay was performed for both parts of the extract, using plant pathogenic bacteria, namely, Erwinia sp., Pseudomonas sp., and Bacillus sp.
The antimicrobial profile was examined and results showed that the extracts showed non-antimicrobial effect before UV irradiation, and antimicrobial effect after UV exposure. Also, those that were active against pathogenic bacteria were more active after UV exposure. This is mostly attributed to a high optical energy of UV irradiation that subsequently had a significant impact on the electron transitions in the molecules of the extract rendering some of them more effective in their antibacterial action.
This short communication was the first report where the UV can alter the antimicrobial profile of cyanobacterial extracts. This is a novel approach in enhancing antibacterial activity. Future molecular investigations will be conducted to further characterize the isolate whose extract showed the highest response to UV treatment.