Distribution and diversity of magnetotactic bacteria in sediments of the Yellow Sea continental shelf

Magnetotactic bacteria (MTB) are cosmopolitan and ubiquitous in sediments of freshwater and marine habitats. Most studies of marine MTB have concerned intertidal zones, and there have been few reports of MTB from seafloor sediments. The objective of this study was to investigate the diversity and spatial distribution of MTB on the continent shelf of the Yellow Sea. Sediments from the continental shelf were collected from the Yellow Sea in August 2015 (summer) and January 2016 (winter). Magnetotactic bacteria were enriched by a permanent magnet. The number of MTB was counted. The diversity of MTB was identified based on high-throughput sequencing and Silva database and nt/nr database. Environmental factors including bottom temperature and salinity, total carbon (TC), total nitrogen (TN), total sulfur (TS), total organic carbon (TOC), concentration of iron, and the sediment grain size were measured. Magnetotactic bacteria were distributed widely in the Yellow Sea, at abundances of 5-2400 ind./dm(3) in summer and 5-820 ind./dm(3) in winter. The dominant MTB at most sampling stations were cocci, although rod-shaped MTB dominated at one station (H17). High-throughput sequencing distinguished 2669 reads for putative MTB in summer and 3271 in winter, and these were classified into 72 operational taxonomic units (OTUs). In both summer and winter, most reads (> 74%) and OTUs (> 50%) of putative MTB belonged to the Nitrospirae. The MTB abundance was significantly correlated with sediment grain size. The MTB abundance was highest at station H17, where the sediment grain size was larger than at other stations. We present a systematic assessment of the spatial distribution and diversity of MTB in sediments of the continental shelf of the Yellow Sea. Our data suggest that diverse MTB are widely distributed in the seafloor sediment of the Yellow Sea, with Nitrospirae likely being the dominating group, and that the abundance of MTB are influenced by sediment grain size.