[B-CG07] Frontier in Biology and Paleobiology of Fossilized Micro-organisms

[BCG07-P03] Diverse benthic foraminiferal assemblages, dominant in non-sedimentary bacterial mats

*Maki Kayamori¹, Yoshiyuki Ishitani², Hidetaka Nomaki² (1.The university of Tokyo, 2.Japan Agency for Marine-Earth Science and Technology)

Keywords:Foraminifera, bacterial mat, feeding habit, methane seep, chemosynthesis-based ecosystem, microbial symbiosis

The ecology of cold seep off Hatsushima Island in western Sagami Bay, was well studied with large multicellular organisms and prokaryotes, but those of small unicellular eukaryotes remain unclear. In the poor oxygen non-sedimentary bacterial mats, we found unexpected high diversity and rich abundance of foraminifers which is usually abundant in aerobic central Sagami Bay.
This study aimed to investigate how foraminifers living on the non-sedimentary bacterial mats have adapted to cold seep environments. Four bacterial mats were examined to assess foraminiferal species composition, bacterial communities, and habit characteristics.
16S amplicon analysis indicated clear differences in microbial communities between the bacterial mats and sediments, with Arcobacter and methane-oxidizing bacteria being more abundant in bacterial mats and sediments, respectively.
The results of Transmission electron microscope (TEM) showed no evidence of bacterial feeding within foraminiferal phagosomes. However, bacteria were observed gathering outside the pores of their carbonate shells, possibly methane-oxidizing bacteria because of its characteristic intracellular membrane structure. These bacteria is more abundant in sediments from 16S amplicon analysis, suggesting strong association between foraminifers and methane-oxidizing bacteria.
These findings suggest that there may be an exchange of materials between these foraminifers and microorganisms.