Microbes in Groundwater of a Volcanic Mountain, Mt. Fuji; 16S rDNA Phylogenetic Analysis as a Possible Indicator for the Transport Routes of Groundwater

Abstract

Huge groundwater reserves are under the foot of Mt. Fuji, the tallest volcanic mountain in Japan, and the residence time of the groundwater as estimated from the ³⁶Cl/Cl isotope ratio is in the range of 20–35 years. All springwater samples contain nearly saturated concentrations of oxygen. The groundwater field was separated into four areas based on regional slopes of the groundwater table and estimated groundwater flow directions. Springwater samples showed that physicochemical characteristics of the groundwater in the region are relatively constant; Ion concentrations were characterized as the Ca-HCO₃ type, irrespective of location at the foot of the mountain. The density of prokaryotes in the springwater, which was in the range of 10²–10⁴ cells mL⁻¹, was low compared with any other groundwater so far reported. Although the density of prokaryotes was low, retrieved clones show that the prokaryotes belonged to eight bacterial and two archaeal phyla, and included both aerobic and obligate anaerobic prokaryotes. Some retrieved clones were related to thermophilic prokaryotes, which are optimally adapted to temperatures greater than 40°C. This finding suggests that at least some of the source of the groundwater was located at a depth of 600 m or greater, based on a temperature gradient of 4°C/100 m. This depth is far below the lava layer which was taken to be a substantial pool of groundwater. Microbiological information may provide insight into the transport route of groundwater until it emerges.

Keywords:

• gene sequencing
• prokaryote
• transport route of groundwater
• volcanic springwater

Funding

This study was partly supported by JSPS KAKENHI Grant Number 23241016 and 26257402 and by the Foundation for the Riverfront Research Center and River Found in Charge of River Foundation, Japan. This study was conducted with the partial support of Joint Research Grant for the Environmental Isotope Study of Research Institute for Humanity and Nature.