Articles | Volume 13, issue 23
Research article
30 Nov 2016
Research article |  | 30 Nov 2016

Archive of bacterial community in anhydrite crystals from a deep-sea basin provides evidence of past oil-spilling in a benthic environment in the Red Sea

Yong Wang, Tie Gang Li, Meng Ying Wang, Qi Liang Lai, Jiang Tao Li, Zhao Ming Gao, Zong Ze Shao, and Pei-Yuan Qian

Abstract. In deep-sea sediment, the microbes present in anhydrite crystals are potential markers of the past environment. In the Atlantis II Deep, anhydrite veins were produced by mild mixture of calcium-rich hydrothermal solutions and sulfate in the bottom water, which had probably preserved microbial inhabitants in the past seafloor of the Red Sea. In this study, this hypothesis was tested by analyzing the metagenome of an anhydrite crystal sample from the Atlantis II Deep. The estimated age of the anhydrite layer was between 750 and 770 years, which might span the event of hydrothermal eruption into the benthic floor. The 16S/18S rRNA genes in the metagenome were assigned to bacteria, archaea, fungi and even invertebrate species. The dominant species in the crystals was an oil-degrading Alcanivorax borkumensis bacterium, which was not detected in the adjacent sediment layer. Fluorescence microscopy using 16S rRNA and marker gene probes revealed intact cells of the Alcanivorax bacterium in the crystals. A draft genome of A. borkumensis was binned from the metagenome. It contained all functional genes for alkane utilization and the reduction of nitrogen oxides. Moreover, the metagenomes of the anhydrites and control sediment contained aromatic degradation pathways, which were mostly derived from Ochrobactrum sp. Altogether, these results indicate an oxic, oil-spilling benthic environment in the Atlantis II basin of the Red Sea in approximately the 14th century. The original microbial inhabitants probably underwent a dramatic selection process via drastic environmental changes following the formation of an overlying anoxic brine pool in the basin due to hydrothermal activities.

Short summary
Mild eruption of hydrothermal solutions on deep-sea benthic floor can produce anhydrite crystal layers, where microbes are trapped and preserved for a long period of time. These embedded original inhabitants will be biomarkers for the environment when the hydrothermal eruption occurred. This study discovered a thick anhydrite layer in a deep-sea brine pool in the Red Sea. Oil-degrading bacteria were revealed in the crystals with genomic and microscopic evidence.
Final-revised paper