Stimulation of Methanotroph Activity by Cu-Substituted Borosilicate Glass

Abstract

Previous investigations have shown that bacteria can derive benefits from elements within mineral assemblages associated with/or proximal to their point of attachment; however to date, no study has shown a direct connection between mineral dissolution and the biological oxidation of the greenhouse gas methane (CH₄). Here we investigate linkages between the Cu content of silicate glasses (Si-glasses) and CH₄ oxidation rates in Methylosinus trichosporium OB3b, a type II methanotroph. A series of batch growth experiments were performed under varying solid phase Cu (0, 80, 200, 400, and 800 ppm Cu) and initial aqueous phase methane concentrations (40, 70, and 130 nM CH₄). Under near equilibrium conditions, the release of Cu from the glasses increased in association with M. trichosporium OB3b activity. The acquisition of Cu from the glasses directly influenced CH₄ oxidation rates of M. trichosporium OB3b, presumably by promoting the expression and activity of copper-containing particulate methane monooxygenase (pMMO), the most efficient MMO for methane oxidation produced. Highest CH₄ oxidation rates were observed in glasses with 80 ppm Cu. However, rates generally displayed an inverted-U relationship with solid-phase Cu concentration; i.e., rates were lower with solid phase Cu concentrations < 80 ppm or > 200 ppm. We conclude that in situ methanotroph activity in soils and sediments is strongly influenced by ambient solid-phase Cu concentrations, which has important implications to interpreting greenhouse gas flux data in geologic settings.

Keywords:

• borosilicate glass
• copper
• dissolution
• methane oxidation
• Methylinosinus trichosporium OB3b

Acknowledgments

The authors would like to thank Charles W. Knapp for instruction and advice on methanotroph culturing, Peter C. Burns for use of the Bruker D8 Discovery powder X-ray diffractometer, David Moore for assistance with the LEO 1550 field emission SEM, and two anonymous reviewers for their insightful comments. The authors also acknowledge support for this research from NSF Biogeosciences (EAR 0433980 awarded to Roberts and Graham), NSF Low Temperature Geochemistry and Geobiology (EAR 0750009 awarded to Fowle, Roberts and Graham, UK NERC (NE/F00608X/1 awarded to Graham), and KU Geology Associates (Fowle).