Microbial Processes Forming Daily Lamination in an Aragonite Travertine, Nagano-yu Hot Spring, Southwest Japan

Abstract

An aragonite travertine at Nagano-yu hot spring, SW Japan, exhibits clear sub-millimeter-order lamination that resembles ancient ministromatolites. Thirty-three hours of continuous observation showed that the lamination is formed daily with no changes in physicochemical properties except light intensity. Phylotype analysis and fluorescence in situ hybridization indicate that Hydrogenophaga sp. is dominant and concentrated in diurnal layers containing abundant extracellular polymeric substances. Growth of Hydrogenophaga sp. is activated in the daytime, likely due to extracellular polymeric substance production by cyanobacterial photosynthesis. Daytime development of Hydrogenophaga-dominant biofilms, and the concurrent inhibiting effect on aragonite precipitation, explains the daily lamination observed.

Keywords:

• Aragonite travertine
• daily lamination
• cyanobacteria
• Hydrogenophaga sp.
• stromatolite

ACKNOWLEDGMENTS

We thank two anonymous reviewers for giving a number of constructive comments that improved the manuscript. We are grateful to Yasuhiro Shibata for SEM analysis, Hayami Ishisako for preparing thin sections and Yukihisa Kudo for providing geological information of Nagayu area. Support and information were kindly provided by the owners of the Nagano-yu hot spring. 33 h observations were conducted with supporting of the laboratory members. We thank Dr. Jennifer Piehl (Wight Science Right, Nevada, USA) for editing English. This study was supported by grants-in-aid from the Japanese Ministry of Education and Science (to TO and AK), and the Program for Enhancing Systematic Education in Graduate Schools of Hiroshima University.