Marine sponge Discodermia calyx consisting of highly complex consortia is a rich and important source of biologically active compounds containing calyculins as the major cytotoxic compounds. However, the low content of active constituents makes it unsuitable to separate enough amounts of active compounds directly from marine sponge. Although the symbiotic microbes are the main producers of active compounds, the vast majority of them cannot be cultured under laboratory conditions. This limits the use of isolation and pure culture of symbiotic microbes to get active compounds from marine sponge. Functional metagenomics, exploring uncultured environmental microorganisms by extracting the genomic DNA directly from marine sponge without any culture or isolation steps, has been proven to be a practical approach to search for unique bioactive small molecules and the corresponding functional genes from marine sponge Discodermia calyx. The biological active constituent of Discodermia calyx separated before February 2013 was summarized. The application of culture-independent functional metagenomics in the Discodermia calyx harboring large populations of uncultured symbiotic microbes was reported. This corroborates the most attractive potential application of functional metagenomics in searching for unique bioactive small molecules and interesting functional genes from Discodermia calyx and other marine sponges. To provide a practical and promising approach to study the Chinese marine sponge-a reservoir pool of biological active compounds and interesting functional genes.

Key words: marine sponge Discodermia calyx, active constituent, functional metagenomics, culture-independent