Horizontal and vertical distribution of dimethylsulfoniopropionate (DMSP) producing and catabolizing bacteria in the East China Sea

Abstract:

[Objective] Dimethylsulfoniopropionate (DMSP) and its cleavage product dimethyl sulfide (DMS) play important roles in sulfur cycle of the marine environment. At present, some studies focus on the distribution of DMSP catabolizing bacteria, while studies on DMSP producing bacteria are just beginning. The objective of this study was to analyze the horizontal and vertical (1000 m depth) distribution of DMSP producing and catabolizing bacteria as well as genes in the East China Sea, and to study their responses to environmental parameters. [Methods] We quantified the abundance of microplankton by using flow cytometry. We measured the abundance of DMSP producing (dsyB and mmtN) and catabolising (dddP and dmdA including C/2 and D/1 subclade) genes and organisms by qPCR and high-throughput amplicon sequencing. [Results] The abundances of Synechococcus, Prochlorococcus, picoeukaryotes and heterotrophic bacteria increased and then decreased in the vertical profile with maximum located at 30-50 m depth. Surface water samples (~4 m) possessed the highest abundance of DMSP producing and catabolizing genes as well as the abundance of DMSP producers (Alteromonas, Phaeobacter and Pelagibaca). With increasing water depth, the abundances of DMSP producing and catabolizing genes and organisms increased and then decreased with peak values at the 100-150 m depth. The abundance of DMSP catabolizing genes decreased rapidly in the water below 100 m depth. However, the abundance of DMSP producing genes decreased slowly in the water below 100 m depth and even increased in the waters from 500 m to 1022 m depth. In contrast, the abundances of DMSP producing and catabolizing genes and organisms did not show apparent horizontal distribution patterns. The bacterial community composition showed significant difference between shallow water (≤100 m) and deep water (>100 m), and the relative abundance of the Flavobacteriia, Actinobacteria and Cyanobacteria in the shallow water were higher than that in the deep water, in contrast with an opposite trend for the Alphaproteobacteria in the deep water. [Conclusion] Bacterial communities differed significantly between waters below and above the 100 m depth. The surface water possessed the highest abundance of DMSP producing and catabolizing bacteria, followed by the 100-150 m water, with DMSP producing and catabolizing bacteria showing significantly different variation trends in the waters of 100-1022 m depth.