The Catalytic Effect of the Heterotrophic Bacterium Virgibacillus marismortui on Basaltic Rock Dissolution Under Excess Nutrient Conditions

Abstract

Biotic and abiotic batch experiments were performed in the presence of excess nutrients (N and P) and basaltic rocks in the medium under various conditions (NA, non-agitated; A, agitated). Changes in solution chemistry were monitored to characterize the influence of aerobic heterotrophic bacteria (Virgibacillus marismortui) on the dissolution rates and mechanisms of two basaltic rocks collected from King George (BAn; basaltic andesine) and Deception Island (BD, basalt), Antarctica. The presence of bacteria in the medium accelerated dissolution of basaltic rocks by a factor of 1.5 to 3 depending on both the rock composition and experimental conditions. The calculated linear element release rates in the biotic experiments (B, biotic) are enhanced in comparison with abiotic systems (A, abiotic) in the order: BD-B-NA > BD-B-A > BAn-B-NA. Unlike the abiotic reference experiments (BD-A-NA; BD-A-A, BAn-A-NA) with pH shifts of less than 0.5 units an accelerated release of Si, Ca, Mg, Fe and Al coincided with an increase in protein concentrations and a marked decrease in pH in the biotic experiments. As indicated by solution acidity, element release, trends of the reactive fluids and surface chemistry of the reacted rock samples, the catalytic effect of bacteria on mineral dissolution reactions was predominantly acidification due to bacterial metabolism. The major catalytic effect of acidification on mineral dissolution was likely suppressed by ammonification, resulting in a pH increase in the reactive fluid. The absence of secondary phases (e.g. Fe and Al oxyhydroxides) on the surface of biotically reacted rock particles and the presence of divalent cations (i.e. Ca and Mg) on the cell surfaces further show the role of the bacteria and associated organic ligands for metal-complexation reactions during basalt dissolution. This study shows that aerobic heterotrophic bacteria may play a critical role for acidity driven silicate dissolution in environments rich in nitrogenated organic compounds and may even influence the amount of Ca and Mg being released from Ca and Mg rich silicates to environments.

Keywords:

• Aerobic heterotrophic bacteria
• ammonification
• basalt
• dissolution

Acknowledgments

This study was carried under the auspices of Presidency of The Republic of Turkey, supported by the Ministry of Industry and Technology, and coordinated by Istanbul Technical University (ITU) Polar Research Center (PolReC). This study was in the frame of bilateral agreement with Polish Institute of Biochemistry and Biophysics (IBB) and PolReC. We would like to thank to 42nd expedition crew for their hospitality and help in Henryk Arctowski Polish Antarctic Station. Additional funding comes from Istanbul Technical University Research Division (ITU-BAP) grant to N. Balci (41729). ICP-MS analysis and SEM images with EDS spectra were carried out at ACME Laboratory, Canada and at Bosphorous University, respectively. XRD and ICP-OES analysis were carried out at ITU. The authors thank two anonymous reviewers for their constructive comments, which greatly improved the manuscript, and Dr. Raif Kandemir for providing additional basalt sample.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Presidency of The Republic The Ministry of Industry and Technology, and coordinated by Istanbul Technical University (ITU) Polar Research Center (PolReC).