RELEASE OF DIMETHYLSULFIDE FROM DIMETHYLSULFONIOPROPIONATE BY PLANT-ASSOCIATED SALT-MARSH FUNGI

The range of types of microbes with dimethylsulfoniopropionate (DMSP) lyase capability (enzymatic release of dimethylsulfide [DMS] from DMSP ) has recently been expanded from bacteria and eukaryotic algae to inc lude fungi (a species of the genus Fusarium [M, K, Bacic and D, C, Yoc h, Appl, Environ, Microbiol. 64:106-111, 1998]), Fungi (especially asc omycetes) are the predominant decomposers of shoots of smooth cordgras s, the principal grass of Atlantic salt marshes of the United States. Since the high rates of release of DMS from smooth cordgrass marshes h ave a temporal peak that coincides with peak shoot death, we hypothesi zed that cordgrass fungi were involved in this DMS release, We tested seven species of the known smooth cordgrass ascomycetes and discovered that six of them exhibited DMSP lyase activity. We also tested two sp ecies of ascomycetes from other DMSP-containing plants, and both were DMSP lyase competent, For comparison, we tested 11 species of ascomyce tes and mitosporic fungi from halophytes that do not contain DMSP; of these 11, only 3 were positive for DMSP lyase. A third group tested, m arine oomycotes (four species of the genera Halophytophthora and Pythi um, mostly from mangroves), showed no DMSP lyase activity, Two of the strains of fungi found To be positive for DMSP lyase also exhibited up take of DMS, san apparently rare combination of capabilities, In concl usion, a strong correlation exists between a fungal decomposer's abili ty; to catabolize DMSP via the DMSP lyase pathway and the host plant's production of DMSP as a secondary product.