IMPACT OF BUFFERS ON MYCOGENIC MANGANESE OXIDE FORMATION

Microbially-mediated reductive dissolution and oxidative precipitation of manganese (Mn) oxides commonly controls Mn (IV/III) (hydr)oxide formation in natural systems [1,2]. Most biogenic Mn(IV/III) (hydr)oxides are highly reactive materials [1,2] that can exert a large effect on trace metal concentrations via redox, adsorption, and coprecipitation processes [3]. Mn(II)-oxidizing bacteria and fungi may promote the precipitation of Mn oxides in many natural and metal-polluted systems, such as coal mine drainage remediation sites. Laboratory-based studies of microbiological systems have often used biologically inert Good’s Buffers (e.g., HEPES, MOPS, MES, etc.) to control for solution pH [2]. However, a recent study of abiotic Mn oxides indicates that Good’s Buffers may reduce structural Mn, thereby altering Mn oxide structures [4]. Furthermore, the pH of natural systems are commonly controlled by carbonate buffers (not Good’s Buffers), and Mn oxide formation can be altered by solution chemistry.

Using a combination of X-ray diffraction, Fourier-transform infrared spectroscopy, and extended X-ray absorption fine structure spectroscopy, we are investigating the structures of Mn oxides produced during Mn oxidation by four Mn(II)-oxidizing Ascomycete fungi species in a buffer-free flow-through system and in closed- and flow through-systems buffered by HEPES or carbonate. We find that the buffer type affects fungal growth behaviors as well as Mn oxide production, with specific effects distinct for each species. For example in a calcium carbonate buffer, Stagonospora sp. SRC1lsM3a grows and oxidizes Mn(II) faster than in HEPES buffer which has traditionally been used by most studies of bacteriogenic and mycogenic Mn oxide formation. In addition, the effect of rehydration, to mimic wet and dry cycles, will be discussed. These results highlight the importance of in situ research under conditions that closely mimic natural systems to better constrain our understanding of the impact and fate of contaminants and nutrients in the environment.

[1] Bargar et al. (2009) Geochim Cosmochim Acta 73, 889-910.

[2] Grangeon et al. (2010) Am. Mineral. 95, 1608-1616.

[3] Brown and Parks (2001) Int. Geol. Rev. 43, 963-1073.

[4] Elzinga and Kustka (2015) Env. Sci. Technol. 49, 4310-4316.