Bacteria associated with algae play a crucial role in the ecological balance of marine ecosystems. Actinomycetes have many advantageous characteristics that increase the bioavailability of vital nutrients in soil and regulate the growth of microbial pathogens. This study aimed to identify the culturable actinomycetes, associated with some algal samples from the Red Sea and investigate their antimicrobial and antioxidant activities. The actinomycetes were isolated from four algal species collected from Yanbu cityon starch nitrate agarmedium supplemented with 10% NaCl and tested for their antimicrobial activity against a panel of pathogenic multidrug-resistant bacteria and for their antioxidant potential using appropriate assays. The collected Algae were identified as Ulva lactuca and Codium tomentosum (green algae), Padina gymnospora (brown algae) and Hypnea valentia (red algae). The results demonstrated that out of 4 different algal samples collected from the Red Sea, 15 filamentous bacterial isolates were obtained, purified and screened for antibacterial activities. Five isolates showed detectable antibacterial activities using the agar plug diffusion assay. Excellent antibacterial activities were recorded by the isolate RAD3 against Staphylococcus aureus, Streptococcus pyogenes and Enterococcus faecalis in addition to Escherichia coli. At the same time, it exhibited lower antimicrobial activity against Pseudomonas aeruginosa, Salmonella typhi, Shigella sonnei and Serratia marcescens. The Minimal Inhibitory Concentrations (MICs) of the RAD3 extract were ranged from 50-100 µg/ml for the tested bacterial pathogens. No antibacterial activity was recorded against Klebsiella pneumonia and Acinetobacter baumannii. The isolate RAD3was the most active in bacterial inhibition and prevented E. faecalis biofilm formation by 63% and exopolymeric substances (EPS) by 47%. The ethyl acetate extracts of the five selected bacteria showed promising antioxidant potential by scavenging DPPH (2,2-diphenyl-1-picrylhydrazyl) method. Out of the 5 chosen bacteria, RAD3 showed 66.37% free radical scavenging with EC50 = 29.0 µg/ml and the results were compared to the positive control and the synthetic antioxidant Butylated Hydroxytoluene (BHT) which showed 96% free radical scavenging with EC50 = 19.7 µg/ml. The 5 chosen bacterial isolates were morphologically characterized and genetically identified by the analysis of 16S rDNA as species belonging to the genus Streptomyces. In conclusion, these findings highlight the potential of bacteria associated with the Red Sea algae as a source of novel antimicrobial and antioxidant compounds for food and medicine industries.
Reda Amasha (Fri,) studied this question.