Microbial production and consumption of dimethyl sulfide (DMS) in a sea grass (Zostera noltii)-dominated marine intertidal sediment ecosystem (Bassind'Arcachon, France)

The relation between net dimethyl sulfide (DMS) production and changes in n ear surface (0-5 mm) oxygen concentrations in a sea grass (Zostera noltii H ornem)-covered intertidal sediment ecosystem was examined during a diel cyc le. Sediment covered with Zostera was found to be more oxygenated than unco vered sediment during the period of photosynthesis. This phenomenon was pro bably caused by radial oxygen loss of the Zostera root-rhizome system. The population sizes of the three functional groups of microbes mainly responsi ble for the concentration of DMS, the dimethylsulfoniopropionate (DMSP)-dem ethylating, DMSP-cleaving and DMS-oxidizing bacteria. were quantified by mo st probable number (MPN) methodologies. Sediments with Zostera supported su bstantially higher populations of both aerobic (149 x 10(6) cm(-3) DMSP-uti lizing and 0.4 x 10(6) cm(-3) DMS-oxidizing) and anaerobic (43 x 10(6) cm(- 3) DMSP-utilizing and 0.4 x 10(6) cm(-3) DMS-oxidizing) microorganisms than sediments without Zostera (DMSP-utilizing aerobes and anaerobes both 2 x 1 0(6) cm(-3) and DMS-oxidizing aerobes and anaerobes both 0.2 x 10(6) cm(-3) ). Experiments conducted with sediment cores and sediment slurries suggeste d that the net production of DMS ill these sediments was significantly lowe r during oxic periods than during anoxic periods. Intact sediment cores wit h and without Zostera produced DMS when incubated under anoxic/dark conditi ons (97.0 and 53.6 nmol DMS m(-2) h(-1). respectively), while oxic/light-in cubated cores did not produce detectable amounts of DMS. In addition, kinet ic parameter values (V-max and K-m) fur DMSP degradation in cell suspension s of isolated DMSP-demethylating and DMSP-cleaving bacteria were measured a nd compared to documented values for other strains. Both V-max and K-m valu es for DMSP-demethylating organisms were Found to be relatively low (14.4-2 0.1 nmol DMSP mg protein(-1) min(-1) and 4.1-15.5 mu M, respectively) while these parameter values varied widely in the group of the DMSP cleaving org anisms (6.7-1000 nmol DMSP mg protein(-1) min(-1) and 2-2000 mu M respectiv ely). It was hypothesized that a diel rhythm in DMS emission occurred, with a relatively low net production during the day and a high net production d uring the night. Environmental changes which result in increased anoxic con ditions in coastal sediments, such as an increase in eutrophication, may th erefore result in increased atmospheric DMS emission rates. (C) 2000 Federa tion of European Microbiological Societies. Published by Elsevier Science B .V. Ail rights reserved.