Impact of Organic Carbon Electron Donors on Microbial Community Development under Iron- and Sulfate-Reducing Conditions

Abstract

Although iron- and sulfate-reducing bacteria in subsurface environments have crucial roles in biogeochemical cycling of C, Fe, and S, how specific electron donors impact the compositional structure and activity of native iron- and/or sulfate-reducing communities is largely unknown. To understand this better, we created bicarbonate-buffered batch systems in duplicate with three different electron donors (acetate, lactate, or glucose) paired with ferrihydrite and sulfate as the electron acceptors and inoculated them with subsurface sediment as the microbial inoculum. Sulfate and ferrihydrite reduction occurred simultaneously and were faster with lactate than with acetate. 16S rRNA-based sequence analysis of the communities over time revealed that Desulfotomaculum was the major driver for sulfate reduction coupled with propionate oxidation in lactate-amended incubations. The reduction of sulfate resulted in sulfide production and subsequent abiotic reduction of ferrihydrite. In contrast, glucose promoted faster reduction of ferrihydrite, but without reduction of sulfate. Interestingly, the glucose-amended incubations led to two different biogeochemical trajectories among replicate bottles that resulted in distinct coloration (white and brown). The two outcomes in geochemical evolution might be due to the stochastic evolution of the microbial communities or subtle differences in the initial composition of the fermenting microbial community and its development via the use of different glucose fermentation pathways available within the community. Synchrotron-based x-ray analysis indicated that siderite and amorphous Fe(II) were formed in the replicate bottles with glucose, while ferrous sulfide and vivianite were formed with lactate or acetate. These data sets reveal that use of different C utilization pathways projects significant changes in microbial community composition over time that uniquely impact both the geochemistry and mineralogy of subsurface environments.

Electron Donor Utilization and Secondary Mineral Formation during the Bioreduction of Lepidocrocite by Shewanella putrefaciens CN32

“…The presence of specific electron donors has been shown to have significant impacts on the development of microbial communities and the formation of Fe(II)-bearing minerals in laboratory based-experiments and in-situ studies in subsurface environments [52,53,[93][94][95][96]. Likewise, in this study we observe that specific electrons donors lead to the formation specific Fe(II)-bearing secondary minerals during DIR of lepidocrocite by S. putrefaciens CN32.…”

Impacts of leachates from livestock carcass burial and manure heap sites on groundwater geochemistry and microbial community structure

“…However, the rarefaction curves indicated that species richness was generally higher in samples from the carcass burial site than in those from the manure heap ( S2 Fig ). These results suggested that the anoxic and anaerobic conditions and the leachate chemical compositions (e.g., various organic acids) at the carcass burial site might have created metabolic complexities that supported an increase in bacterial diversity [ 28 ].…”

Viral and bacterial community responses to stimulated Fe(III)‐bioreduction during simulated subsurface bioremediation

“…Flexible metabolisms have been observed in many Fe(III)‐reducing bacteria, which consolidates adaptation to environmental fluctuations of electron donors and acceptors (Melton et al ., ) and the bacterial community patterns in Fe(III)‐bioreduction environments have been well documented (Weber et al ., ; Cardenas et al ., ; Kwon et al ., ). In a recent study, acetate addition as electron donor specifically promoted Proteobacteria and Firmicutes as Fe(III) reducers in the system (Kwon et al ., ). Cardenas and colleagues () observed more Delta‐ and Beta‐Proteobacteria in the acetate‐treated zones than in the background area.…”