Degradation of the organic carbon associated with Biogenic Iron (Oxyhydr)oxides by fermenting cultures enriched from Lake Constance

Biogenic iron (oxyhydr)oxides (BIOS) are iron–organic carbon (OC) coprecipitates formed by Fe(II)-oxidizing bacteria that can be found in diverse terrestrial and aquatic environments, such as acid mine drainage, wetlands, and river systems. These biogenic iron minerals may contribute to effectively store OC as a “rusty sink”, where 21.5 ± 8.6% of the total OC is associated with iron minerals in sediments (Whitaker et al. 2021, Lalonde et al. 2012). The properties of BIOS (OC content, association via sorption or coprecipitation, surface area) are determined by the environmental conditions and the microorganisms they are formed by, influencing its effectiveness as a rusty sink. BIOS are rich in OC, which affects its physical properties (e.g. surface area, charge, reactivity) (Whitaker et al. 2021, Sowers et al. 2019). Thus, the bioavailability of the OC associated with BIOS (OC_BIOS) might impact its properties as a carbon sink. Preliminary tests show that Fe(III)-reducing bacteria are not able to oxidize OC_BIOS as the sole electron donor when coupling to Fe(III) reduction. However, in suboxic and anoxic environments, fermenters are known to play an important role in the degradation of OC and could therefore potentially use the OC_BIOS.

Given the importance of BIOS as a carbon sink, we enriched a consortium of fermenting microorganisms from sediments of Lake Constance with different carbon sources (simple to recalcitrant) to test their ability to degrade OC_BIOS. We measured gas emissions (CO₂, CH₄,H₂), volatile fatty acid concentration, and DOC to follow the degradation of OC and the production of metabolites. Initial results indicated differential production of gases and organics depending on the amended carbon sources. We are determining the changes in the composition of the microbial community with 16S rRNA Illumina Sequencing. In the next step, we will test the ability of these fermentative enrichment cultures to degrade the OC_BIOS of the photoferrotroph Rhodopseudomonas palustris TIE-1 (Jiao et al. 2005) and the nitrate-reducing Fe(II)-oxidizing culture KS (Straub et al. 1996).

 

Whitaker, A. H., Austin, R. E., Holden, K. L., Jones, J. L., Michel, F. M., Peak, D., Thompson, A., & Duckworth, O. W. (2021). The structure of natural biogenic iron (oxyhydr)oxides formed in circumneutral pH environments. Geochimica et Cosmochimica Acta, 308, 237–255.

Lalonde, K., Mucci, A., Ouellet, A., & Gélinas, Y. (2012). Preservation of organic matter in sediments promoted by iron. Nature, 483(7388), 198–200.

Sowers, T. D., Holden, K. L., Coward, E. K., & Sparks, D. L. (2019). Dissolved Organic Matter Sorption and Molecular Fractionation by Naturally Occurring Bacteriogenic Iron (Oxyhydr)oxides. Environmental Science & Technology, 53(8), 4295–4304.

Jiao, Y., Kappler, A., Croal, L. R., & Newman, D. K. (2005). Isolation and characterization of a genetically tractable photoautotrophic Fe(II)-oxidizing bacterium, Rhodopseudomonas palustris strain TIE-1. Applied and environmental microbiology, 71(8), 4487–4496.

Straub, K. L., Benz, M., Schink, B., & Widdel, F. (1996). Anaerobic, nitrate-dependent microbial oxidation of ferrous iron. Applied and Environmental Microbiology, 62(4), 1458–1460.