Adaptation of spherical multicellular magnetotactic prokaryotes to the geochemically variable habitat of an intertidal zone

Abstract

A combination of microscopic, molecular and biogeochemical methods was used to study the structure, phylogenetics and vertical distribution of spherical multicellular magnetotactic prokaryotes (MMPs) of intertidal sediments in the Yellow Sea. These MMPs were 5.5 μm in diameter and composed of approximately 15-30 cells. They synthesized bullet-shaped magnetites in chains or clusters. Phylogenetic analysis of 16S rRNA gene sequences suggested that these MMPs represent a novel species affiliated to the Deltaproteobacteria. To study their vertical distribution and the relationship to geochemical parameters, sediment cores were collected after the redox potential was measured in situ. The sediments were composed of yellow, grey and black layers from the surface to depth. The spherical MMPs were concentrated near the grey-black layer transition at a depth of 8-12 cm, while coccoid-shaped magnetotactic bacteria near the yellow-grey layer transition at a depth of 3-5 cm. The intertidal MMPs showed a deeper distribution at more reduced environments than coccoid-shaped magnetotactic bacteria, and MMPs in lagoon sediments. Additionally the MMPs were concentrated significantly in layers with high proportion of fine sand and total organic carbon, rich in leachable iron but poor in nitrate. These results show an adaptation of spherical MMPs to the peculiar intertidal sediment habitat.