Abstract
Dimethylsulfoniopropionate (DMSP) is a key organic sulfur compound that is produced by many phytoplankton and macrophytes and is ubiquitous in marine environments. Following its release into the water column, DMSP is primarily metabolised by heterotrophic bacterioplankton, but recent evidence indicates that non-DMSP producing phytoplankton can also assimilate DMSP from the surrounding environment. In this study, we examined the uptake of DMSP by communities of bacteria and phytoplankton within the waters of the Great Barrier Reef (GBR), Australia. We incubated natural GBR seawater with DMSP and quantified the uptake of DMSP by different fractions of the microbial community (>8 µm, 3–8 µm, <3 µm). We also evaluated how microbial community composition and the abundances of DMSP degrading genes are influenced by elevated dissolved DMSP levels. Our results showed uptake and accumulation of DMSP in all size fractions of the microbial community, with the largest fraction (>8 µm) forming the dominant sink, increasing in particulate DMSP by 44–115% upon DMSP enrichment. Longer-term incubations showed however, that DMSP retention was short lived (<24 h) and microbial responses to DMSP enrichment differed depending on the community carbon and sulfur demand. The response of the microbial communities from inside the reef indicated a preference towards cleaving DMSP into the climatically active aerosol dimethyl sulfide (DMS), whereas communities from the outer reef were sulfur and carbon limited, resulting in more DMSP being utilised by the cells. Our results show that DMSP uptake is shared across members of the microbial community, highlighting larger phytoplankton taxa as potentially relevant DMSP reservoirs and provide new information on sulfur cycling as a function of community metabolism in deeper, oligotrophic GBR waters.
Highlights
Introduction published maps and institutional affilDimethylsulfoniopropionate (DMSP) is an important and ubiquitous organic sulfur compound in the marine environment [1]
Dimethylsulfoniopropionate (DMSP), which in the open ocean is predominantly produced by marine phytoplankton and taken up by several groups of marine heterotrophic bacteria [6,7] plays an important role in marine ecosystems
Dimethylsulfoniopropionate (DMSP), which in the open ocean is predominantly produced by marine phytoplankton and taken up by several groups of marine heterotrophic bacteria [6,7] plays an important role in Corals and reef lagoons of the Great Barrier Reef (GBR) are well characterised as dimethyl sulfide (DMS)/P hot spots, due to high local production by corals [47]; limited information exists on DMSP concentration and cycling outside shallow reef waters
Summary
Dimethylsulfoniopropionate (DMSP) is an important and ubiquitous organic sulfur compound in the marine environment [1]. Phytoplankton are the dominant producers of DMSP, intracellular concentrations vary from species to species, ranging from extremely low in cyanobacteria and most diatoms to very high, ~300 pg DMSP cell−1 , in haptophytes and dinoflagellates [2,3,4,5]. In DMSP-producing phytoplankton, DMSP is central to cell metabolism, satisfying up to 71% of the sulfur and 15% of the cells carbon demand [3,6]. For DMSP-associated bacterioplankton, DMSP can account for up to 95% of the sulfur and 15% of the carbon demand [7]. Intracellular or particulate DMSP (DMSPp) is transported from the synthesising cell into the external seawater environment via exudation, viral lysis or cell senescence [14,15,16].
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