Structural Alteration of Humic Acids by Pseudomonas spp. from Deep Terrestrial Subsurface Diatomite Formations in Northernmost Japan

Abstract

Bacterial utilization of humic acids (HAs) was examined under aerobic conditions using Pseudomonas spp. from diatomite from a depth of 250 m below ground level in the Horonobe Underground Research Laboratory. HA decolorization and bacterial aggregation were observed during cultivation when an auxiliary carbon source was added. High-performance size-exclusion chromatography showed that high-molecular-weight HAs were produced. Fourier transform infrared spectroscopy indicated that carboxyl groups and polysaccharide-related substances in HAs were eliminated, while aliphatic structural units and amide groups were added to HAs. These results suggested that Pseudomonas spp. utilize and alter the molecular structure of HAs under aerobic conditions caused by the construction of underground facilities.

Keywords:

• bacterial aggregation
• decolorization
• Fourier transform infrared spectroscopy
• high-performance size-exclusion chromatography
• humic acid
• subsurface bacteria

Acknowledgments

We would like to acknowledge the Japan Atomic Energy Agency (JAEA) for the collection of subsurface groundwater samples in the Horonobe URL. We would also like to thank Dr. Masami Fukushima from the Graduate School of Engineering, Hokkaido University, for the technical advice regarding HA analysis. We appreciate the technical assistance provided by Hiroyuki Tada and Kumiko Nishizawa.

Supplemental Material

Supplemental data for this article can be accessed on the publisher's website.

Additional information

Funding

This work was supported by the Ministry of Economy, Trade, and Industry (METI) of Japan.