Isolation of peptides from Sri Lankan demosponge Axinella donnani

Axinella donnani (Demospongiae (class), Axinellida (order), Axinellidae (family)) is a marine sponge which has shown significant activity in various bioassays such as antibacterial assay, brine shrimp cytotoxicity assay, microalgal lethality assay, larvicidal assay and ichthytoxicity assay. A. donnani has a high endosymbiotic bacterial count and some of these bacterial strains exhibit significant activity against shrimp and human pathogens. The main focus of this study is to discover novel chemicals compounds from A. donnani with potential as drug leads. Presently, three peptides A, B, and C of 3-4 kDa size were isolated from the methanolic extract of A. donnani collected from coastal water in Wennappuwa, Sri Lanka. Peptides were purified using RP-HPLC (Reverse Phase High Performance Liquid Chromatography). The mass spectroscopic analysis using MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization- Time Of Flight) revealed monoisotopic masses of peptides A,B and C 3885.93 Da [M+H]+, 4325.40 Da [M+H]+, and 4883.25 Da [M+H]+ respectively. Number of disulfide bonds were identified as 2, 4 and 5 respectively in peptides A, B and C after reduction and alkylation. Peptide A was subjected to microdilution assay (Stromstedt et al, 2017) against E. coli (ATCC 25922), S. aureus (ATCC 29213), and P. aeruginosa (ATCC 27853). Peptide A inhibited growth of E.coli at a minimum inhibitory concentration (MIC) value 100 µM. The study will continue with peptide sequencing by MSMS, structure elucidation by NMR and further screening of other potential bioactivities of the isolated peptides.