Evidence for the biogenic origin of manganese‐enriched layers in Lake Superior sediments

Abstract

Manganese (Mn) and iron (Fe)-enriched sediment layers were discovered in Lake Superior within, above and below the oxic-anoxic interface. While the role of bacteria in redox reactions with Mn is known to be significant, little information exists about indigenous microbial communities in many freshwater environments. This study examined the bacterial communities of Mn-enriched layers in Lake Superior to identify the potential Mn(II) oxidizers responsible for the formation of Mn oxides. Anaerobic Mn(II) oxidation occurring in the Mn-enriched layers at the oxic-anoxic interface was investigated using Mn(II)-enriched cultures. High-resolution microscopic and spectroscopic investigations provided evidence of the biogenic formation of Mn oxides on cell surfaces. Spectroscopic mapping confirmed high levels of Mn in structures resembling biogenic Mn oxides. These structures were observed in enrichment cultures and in Mn-enriched layer sediment samples, indicating the significance of biogenic Mn oxidation occurring in situ. 16S ribosomal DNA pyrosequencing was used to identify the bacteria potentially responsible for Mnoxide formation in the enrichment cultures and Mn-enriched layers, revealing that the Mn-enriched layer contains classes with known Mn(II)-oxidizing members. Pyrosequencing of bacterial cultures suggested that these bacteria may be Bacillus strains, and that anaerobic microbial-mediated Mn(II) oxidation contributes to the formation of the layers.

Comparative Genomic Analysis of Neutrophilic Iron(II) Oxidizer Genomes for Candidate Genes in Extracellular Electron Transfer

“…Hyphomicrobium spp. were suggested to play a role in Mn(II) oxidation in freshwater sediments (Stein et al, 2001 ; Palermo and Dittrich, 2016 ). In water treatment, filters are often used to remove Fe(II) and Mn(II) by their biological oxidation to form precipitates of Fe(III) and Mn(IV) oxyhydroxides [see reviews on this topic (Gounot, 1994 ; Emerson and De Vet, 2015 )].…”

Organic sulfur from source to sink in low-sulfate Lake Superior

“…Prior investigations of Lake Superior's microbial community have largely focused on photosynthesis in the water column (Fahnenstiel et al 1986;Ivanikova et al 2007;Reed and Hicks 2011;Sheik et al 2022), reflecting the importance of this freshwater resource for drinking, recreation, and hydroelectric power (O'Beirne et al 2017). Sedimentary studies have thus far focused on specialized cycles like those of metals (Dittrich et al 2015;Palermo and Dittrich 2016) and nitrogen (Small et al 2016;Crowe et al 2017). One study even deemed sulfate reduction in Lake Superior sediments as an "insignificant process" (Carlton et al 1989).…”

Organic sulfur from source to sink in low‐sulfate Lake Superior

“…Prior investigations of the Lake Superior sedimentary microbial community have focused on specialized cycles like those of metals (Dittrich et al 2015; Palermo and Dittrich 2016) and nitrogen (Small et al 2016; Crowe et al 2017). Sulfate reduction was deemed “insignificant” in a broader ecological framework (Carlton et al 1989) and sulfur cycling microorganisms received little attention.…”