Diketopiperazine derivatives from Enterobacter cloacae isolated from the Red Sea alga Cystoseira myrica
Noha A Mohammed1, Hossam M Hassan2, Mostafa E Rateb2, Eman F Ahmed3, Usama W Hawas4, Somayah Sameer5, Rainer Ebel5, Mounir M El-Safty6, Mohammed S Abdel Hameed1, Ola H Hammouda1
1 Department of Botany, faculty of Science, Beni-Suief University, Beni-Suief, Cairo, Egypt
2 Department of Pharmacognosy, College of Pharmacy, Beni-Suief University, Beni-Suief, Cairo, Egypt
3 Department of Chemistry of Natural and Microbial Products, National Research Centre, 12311, Dokki, Cairo, Egypt
4 Marine Chemistry Department, Faculty of Marine Sciences, King Abdulaziz University, Jeddah, Saudi Arabia
5 Marine Biodiscovery Centre, University of Aberdeen, Scotland, United Kingdom
6 Central Laboratory for Evaluation of Veterinary Biologics (CLVB), Cairo, Egypt
Eman F Ahmed
Department of Chemistry of Natural and Microbial Products, National Research Centre, Dokki, 12311 Cairo
Source of Support: None, Conflict of Interest: None
This study is an attempt to explore the biological activities of isolated endophytic bacteria from marine sources that were coded A1, A2, and A3 (Padina pavonica), A4 (Cystoseira myrica), A5 (Acanthophora dendroides), and A6 (Sargassum sabrepandum). The bacteria coded C1, C2, and C3 were isolated from the soft coral Nephthea mollis and S1 and S2 were isolates from the sponge Hymedesmia spp. The primary aim of the study was the identification of active compounds.
Materials and methods
The bioactive compounds were extracted using ethyl acetate from nutrient broth media; biological activities of the extracted metabolites and 16S rDNA identification of the most promising isolate were studied. The eight major fractions of the extract showed different composition patterns when identified by liquid chromatography/mass spectrometry analyses.
Results and conclusion
Agar diffusion assay showed inhibitory activities of A4 extracts against the growth of most pathogenic microorganisms. Identification using PCR 16S rDNA and electrophoresis confirmed 98% identity to the Enterobacter cloacae strain GH1 (ac: JF261136.1). Eight compounds out of fifteen in the extract were identified as diketopiperazine derivatives. The maximum growth of E. cloacae was obtained at 30°C, pH 7, with the addition of maltose and KI to the media. The free radical scavenging activity exhibited good antioxidant activity (72.19%, IC 50 = 1.266 mg/ml) on using 2.0 mg/ml of the crude extract. The extract showed a high antiviral activity towards Newcastle disease virus and avian influenza virus A(H5N1).