Mesophilic Mineral-Weathering Bacteria Inhabit the Critical-Zone of a Perennially Cold Basaltic Environment

Abstract

The weathering of silicate in the world's critical-zone (rock-soil interface) is a natural mechanism providing a feedback on atmospheric CO₂ concentrations through the carbonate-silicate cycle. We examined culturable bacterial communities from a critical-zone in western Iceland to determine the optimum growth temperature and their ability to solubilize phosphate-containing minerals, which are abundant within the critical-zone area examined here. The majority of isolated bacteria were able to solubilize mineral-state phosphate. Almost all bacterial isolates were mesophilic (growth optima of 20–45°C), despite critical-zone temperatures that were continuously below 15°C, although all isolates could grow at temperatures associated with the critical-zone (−2.8–13.1°C). Only three isolates were shown to have thermal optima for growth that were within temperatures experienced at the critical-zone. These findings show that the bacteria that inhabit the western Icelandic critical-zone have temperature growth optima suboptimally adapted to their environment, implying that other adaptations may be more important for their long-term persistance in this environment. Moreover, our study showed that the cold basaltic critical-zone is a region of active phosphate mineral-weathering.

Keywords:

• bacteria
• critical-zone
• MPS
• soil microbiology
• weathering

Acknowledgments

We would like to thank Laura Kelly (INRA, France), Victoria Pearson and Emma Sayer (Open University, UK) for comments on this manuscript. In addition, Stephen Summers would like to thank Colin Murrell and Stephane Uroz, whose comments helped polish this study.

Supplemental Material

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

Funding

This work was conducted with support and funding from The Center for Ecology and Hydrology, United Kingdom and The Open University, United Kingdom.