Abstract
Dimethylsulfoniopropionate (DMSP) is one of Earth’s most abundant organosulfur molecules, and bacteria in marine sediments have been considered significant producers. However, the vertical profiles of DMSP content and DMSP-producing bacteria in subseafloor sediment have not been described. Here, we used culture-dependent and -independent methods to investigate microbial DMSP production and cycling potential in South China Sea (SCS) sediment. The DMSP content of SCS sediment decreased from 11.25 to 20.90 nmol g–1 in the surface to 0.56–2.08 nmol g–1 in the bottom layers of 8-m-deep subseafloor sediment cores (n = 10). Very few eukaryotic plastid sequences were detected in the sediment, supporting bacteria and not algae as important sediment DMSP producers. Known bacterial DMSP biosynthesis genes (dsyB and mmtN) were only predicted to be in 0.0007–0.0195% of sediment bacteria, but novel DMSP-producing isolates with potentially unknown DMSP synthesis genes and/or pathways were identified in these sediments, including Marinobacter (Gammaproteobacteria) and Erythrobacter (Alphaproteobacteria) sp. The abundance of bacteria with the potential to produce DMSP decreased with sediment depth and was extremely low at 690 cm. Furthermore, distinct DMSP-producing bacterial groups existed in surface and subseafloor sediment samples, and their abundance increased when samples were incubated under conditions known to enrich for DMSP-producing bacteria. Bacterial DMSP catabolic genes were also most abundant in the surface oxic sediments with high DMSP concentrations. This study extends the current knowledge of bacterial DMSP biosynthesis in marine sediments and implies that DMSP biosynthesis is not only confined to the surface oxic sediment zones. It highlights the importance of future work to uncover the DMSP biosynthesis genes/pathways in novel DMSP-producing bacteria.
Highlights
Dimethylsulfoniopropionate (DMSP) is an organic sulfur compound produced by many marine algae, bacteria, corals, and some plants (Moran and Durham, 2019; Zhang et al, 2019)
The headspace DMS resulting from the alkaline lysis of DMSP was monitored by gas chromatography (GC) with a flame photometric detector (Agilent 7890B GC fitted with a 7693A autosampler) and an HP-INNOWax 30 m × 0.320 mm capillary column (Agilent Technologies J&W Scientific)
Multiple studies revealed that DMSP and DMS concentrations in marine sediment reach ∼1,000-fold higher levels than those in the overlying water column (Nedwell et al, 1994; Wilkening et al, 2019; Williams et al, 2019), suggesting that marine surface sediments are hot spots for DMSP production and catabolism
Summary
Dimethylsulfoniopropionate (DMSP) is an organic sulfur compound produced by many marine algae, bacteria, corals, and some plants (Moran and Durham, 2019; Zhang et al, 2019). Dimethylsulfoniopropionate is ubiquitous in the marine euphotic zone at concentrations ranging from 1 to 100 nM in the open oceans (Dacey et al, 1998; Cui et al, 2015; Galí et al, 2015) to several micromolar in phytoplankton blooms (Van Duyl et al, 1998; Speeckaert et al, 2018) Phytoplankton, such as dinoflagellates, haptophytes, and green algae that contain the highest intracellular DMSP levels (Keller et al, 1989; Curson et al, 2018), are believed to be the main oceanic DMSP producers (Zhang et al, 2019). We quantified the DMSP concentration in the SCS surface and subseafloor sediments, and combined culture-dependent and -independent methods to explore the spatial distribution of DMSP-producing and catabolic bacteria, aiming to reveal (1) the vertical concentration profiles of DMSP in deep-sea sediments, (2) vertical changes of DMSP-producing bacteria groups, and (3) the potential novel DMSP biosynthetic bacteria in the SCS sediments
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