Design and synthesis of marine natural product-based 1H-indole-2,3-dione scaffold as a new antifouling/antibacterial agent against fouling bacteria.

Marine organisms such as seaweeds, sponges and corals protect their own surfaces from fouling by their high anesthetic, repellant, and settlement inhibition properties. Within the marine ecosystem, evolution has allowed for the development of certain antifouling properties. Isatin is a biologically active chemical produced by an Alteromonas sp. strain inhibiting the surface of embryos of the cardiean shrimp Palaemon macrodectylus, which protect them from the pathogenic fungus Lagenidium callinectes. In present study, an antibacterial activity of isatin and its synthetic analogues were evaluated against different fouling bacteria in order to explore the structure activity relationships for the first time. The synthesized compounds along with parent isatin were tested against different ecologically relevant marine microorganisms by using the Kirby-Bauer disc diffusion method. Few synthetically modified isatin exhibited potent inhibitory activity at concentration of 2 µg/disc against Planococcus donghaensis, Erythrobacter litoralis, Alivibrio salmonicida, Vibrio furnisii. Overall, the modified analogues showed stronger activity than the parent marine natural product (isatin) and hence 1H-indole-2,3-dione scaffold has immense potential as future antibacterial/antifouling candidate.

Evaluation of single and joint effect of metabolites isolated from marine sponges, Fasciospongia cavernosa and Axinella donnani on antimicrobial properties.

The biochemical mechanisms that marine sponges have developed as a chemical defense to protect themselves against micro and subsequent macrobiofouling process might comprise a potential alternative for the preventing attack of biofilm forming bacteria. The present study investigated the antimicrobial activity of a series of major secondary metabolites isolated from the sponges Fasciospongia cavernosa and Axinella donnani against fouling bacteria. Secomanoalide (1), dehydromanoalide (2) and cavernosine (3) have been isolated from F. cavernosa. Their structures were determined by MS, (1)H NMR spectra analyses and by comparison with those reported in the literature. The most promising activity was exhibited by the metabolites from A. donnani, that is, cerebroside (5) against three strains Aeromonas hydrophila subsp. salmonicida A449 and Erythrobacter litoralis. Our investigation revealed that combined metabolites 1, 2 and 3 retained strong activity but individual metabolite had moderate activity indicating that activity probably results from synergistic interactions between multiple compounds. The antibacterial screening of compounds 3, 5 and synergistic effect of 1-3 against fouling bacteria has been studied for the first time. Further, isolation of manoalide related compounds and their synergistic screening can be accelerated for the development of new biofilm inhibitors.

Isolation and Characterization of Antibacterial Compound from a Mangrove-Endophytic Fungus, Penicillium chrysogenum MTCC 5108.

Microorganisms, especially endophytic fungi that reside in the tissue of living mangrove plants, seem to play a major role in meeting the general demand for new biologically active substances. During the course of screening for biologically active secondary metabolites from marine microorganisms, an antibiotic compound containing an indole and a diketopiperazine moiety was isolated from the culture medium of Penicillium chrysogenum, (MTCC 5108), an endophytic fungus on the mangrove plant Porteresia coarctata (Roxb.). The cell free culture medium of P. chrysogenum showed significant activity against Vibrio cholerae, (MCM B-322), a pathogen causing cholera in humans. Bioassay guided chemical characterization of the crude extract led to the isolation of a secondary metabolite possessing a molecular formula C19H21O2N3. Its antibacterial activity was comparable with standard antibiotic, streptomycin. This compound (1) was found to be (3,1'-didehydro-3[2″(3'″,3'″-dimethyl-prop-2-enyl)-3″-indolylmethylene]-6-methyl pipera-zine-2,5-dione) on the basis of mass spectrometry, infrared spectroscopy and one and two-dimensional nuclear magnetic resonance analysis.

The sponge-associated bacterium Bacillus licheniformis SAB1: a source of antimicrobial compounds.

Several bacterial cultures were isolated from sponge Halichondria sp., collected from the Gujarat coast of the Indo Pacific region. These bacterial cultures were fermented in the laboratory (100 mL) and the culture filtrate was assayed for antibiotic activity against 16 strains of clinical pathogens. Bacillus sp. (SAB1), the most potent of them and antagonistic to several clinically pathogenic Gram-positive, Gram-negative bacteria and the fungus Aspergillus fumigatus was chosen for further investigation. Analysis of the nucleotide sequence of the 16S rDNA gene of Bacillus sp. SAB1 showed a strong similarity (100%) with the 16S rDNA gene of Bacillus licheniformis HNL09. The bioactive compounds produced by Bacillus licheniformis SAB1 (GenBank accession number: DQ071568) were identified as indole (1), 3-phenylpropionic acid (2) and a dimer 4,4'-oxybis[3-phenylpropionic acid] (3) on the basis of their Fourier Transform Infrared (FTIR), Nuclear Magnetic Resonance (NMR) and Electrospray Ionization Mass Spectrometer (ESI-MS) data. There is a single reference on the natural occurrence of compound 3 from the leaves of a terrestrial herb Aptenia cordifolia in the literature, so to the best of our knowledge, this is a first report of its natural occurrence from a marine source. The recovery of bacterial strains with antimicrobial activity suggests that marine-invertebrates remain a rich source for the isolation of culturable isolates capable of producing novel bioactive secondary metabolites.