pH, redox potential and local biofilm potential microenvironments within <i>Geobacter sulfurreducens</i> biofilms and their roles in electron transfer

Babauta, Jerome T.; Nguyen, Hung D.; Harrington, Timothy D.; Renslow, Ryan; Beyenal, Haluk

doi:10.1002/bit.24538

Cited by 125 publications

(131 citation statements)

References 45 publications

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“…Yu et al reported that the highest mean SOC density (209.9 t C ha -1 ) was recorded from a wetland ecosystem and the lowest (29.0 t C ha -1 ) from a desert ecosystem in China [16]. Due to the greatly reduced supply of O 2 to soil and the decreased organic carbon mineralization rates in the natural wetland, the natural wetland shows a high content of soil organic carbon in the anaerobic environment [17]. In the anaerobic environment, anaerobic microorganisms as well as photosynthesis by submerged macrophytes can create high pH values in the aquatic environment [18].…”

Section: Resultsmentioning

confidence: 99%

Changes in Land Use and their Effects on Soil Properties in Huixian Karst Wetland System

Li¹,

Jin²,

Li³

2017

Pol. J. Environ. Stud.

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To gain a better understanding of the impact from the land-use change in the Huixian karst wetland system, we analyzed soil microflora, enzyme activities, and physicochemical properties from three land-use types (natural wetland, paddy field, and dry farmland). The results showed that soil pH, soil organic carbon, total nitrogen, cation exchange capacity, exchangeable Ca and Mg, and the cellulase and alkaline phosphatase activities in the dry farmland were significantly lower than those in the paddy field and natural wetland (p<0.05). However, soil pH, soil organic carbon, total nitrogen, cation exchange capacity, exchangeable Ca and Mg, and the cellulase and alkaline phosphatase activities made no significant difference to the paddy field and the natural wetland (p>0.05). Moreover, the soil microbial biomass carbon and nitrogen in the dry farmland were also lower than those in the paddy field and natural wetland, although no significant differences were observed (p>0.05). This suggests that, in the alkali condition, natural wetland with high biomass and weak microbial activity may be an important carbon sink. In the CCA biplot, it can be seen that the natural wetland cluster intersects with the paddy field cluster and the dry farmland cluster in the same quadrant (although the paddy field and the dry farmland clusters are separate). Therefore, we concluded that the natural wetland usually was reclaimed as paddy field or dry farmland directly for agricultural output in the Huixian karst wetland system. The paddy field has a waterlogged condition and shows the similar results to natural wetland, which can be regarded as artificial wetland. In view of the similar ecosystem services by paddy fields as substitutes of natural wetland, if the degradation trend of natural karst wetland can't be reversed, the paddy field should be preserved in the Huixian karst wetland system for its ecosystem service.

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Section: Resultsmentioning

confidence: 99%

Changes in Land Use and their Effects on Soil Properties in Huixian Karst Wetland System

Li¹,

Jin²,

Li³

2017

Pol. J. Environ. Stud.

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“…Large pH differences have been recorded in Pseudomonas biofilms, where a difference of 1.4 pH units was measured across distances of 50 m (20). Further pH shifts have been seen across a variety of distances in a range of biofilms grown under different conditions (21)(22)(23). However, in all these cases, the pH shifts are associated with near neutral conditions, and as such, the logarithmic nature of the pH scale means that the modulation of internal pH in response to alkaline conditions represents a significantly more difficult challenge to the microorganisms concerned.…”

mentioning

confidence: 97%

Floc Formation Reduces the pH Stress Experienced by Microorganisms Living in Alkaline Environments

Charles

Rout

Patel

et al. 2017

Appl Environ Microbiol

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The survival of microorganisms within a cementitious geological disposal facility for radioactive wastes heavily depends on their ability to survive the calciumdominated, hyperalkaline conditions resulting from the dissolution of the cementitious materials. The results from this study show that the formation of flocs, composed of a complex mixture of extracellular polymeric substances (EPS), provides protection against alkaline pH values up to 13.0. The flocs were dominated by Alishewanella and Dietzia spp., producing a mannose-rich carbohydrate fraction incorporating extracellular DNA, resulting in Ca 2ϩ sequestration. EPS provided a ϳ10-m thick layer around the cells within the center of the flocs, which were capable of growth at pH values of 11.0 and 11.5, maintaining internal pH values of 10.4 and 10.7, respectively. Microorganisms survived at a pH of 12.0, where an internal floc pH of 11.6 was observed, as was a reduced associated biomass. We observed limited floc survival (Ͻ2 weeks) at a pH of 13.0. This study demonstrates that flocs maintain lower internal pHs in response to the hyperalkaline conditions expected to occur within a cementitious geological disposal facility for radioactive wastes and indicates that floc communities within such a facility can survive at pHs up to 12.0. IMPORTANCE The role of extracellular polymeric substances (EPS) in the survival of microorganisms in hyperalkaline conditions is poorly understood. Here, we present the taxonomy, morphology, and chemical characteristics of an EPS-based microbial floc, formed by a consortium isolated from an anthropogenic hyperalkaline site. Short-term (Ͻ2 weeks) survival of the flocs at a pH of 13 was observed, with indefinite survival observed at a pH of 12.0. Measurements from micro-pH electrodes (10-m-diameter tip) demonstrated that flocs maintain lower internal pHs in response to hyperalkaline conditions (pH 11.0, 11.5, and 12.0), demonstrating that floc formation and EPS production are survival strategies under hyperalkaline conditions. The results indicate how microbial communities may survive and propagate within the hyperalkaline environment that is expected to prevail in a cementitious geological disposal facility for radioactive wastes; the results are also relevant to the wider extremophile community.

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“…Construction and pulling of the individual graphite microelectrodes has been detailed previously. 15 The two microelectrode tips were positioned ∼1 mm apart with the lower one to be used as the microelectrode tip. The higher graphite microelectrode was used as the counter electrode.…”

Section: Methodsmentioning

confidence: 99%

“…After it was visually confirmed that the reactor volume remained clear and unchanged, approximately 20 mL of G. sulfurreducens inoculum was added to the reactor following a previously published method. 15 An immediate current response was observed and, after half a day, the reactor was switched to operate in continuous mode until the end of the experiment. Once a maximum current was observed from the electrode-biofilm, we prepared microelectrodes for insertion into the biofilm reactor.…”

Section: Methodsmentioning

confidence: 99%

Local Current Variation by Depth inGeobacter SulfurreducensBiofilms

Babauta

Beyenal

2014

J. Electrochem. Soc.

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New methods of detecting local extracellular electron transfer rates in electrochemically active biofilms (EABs) are needed to quantify the role of microscale gradients in extracellular electron transfer. We utilized electrode-respiring Geobacter sulfurreducens biofilms as a model EAB to demonstrate local current measurement by depth using microelectrodes with a graphite tip covered by biofilm. We grew G. sulfurreducens biofilms on an electrode (electrode-biofilm) and on the tip of a microelectrode (microelectrodebiofilm) and monitored current generation. The microelectrode-biofilm current was negatively affected by the current produced in the electrode-biofilm; this resulted in a change in current, . We found a 30% decrease in current from the top of the electrode-biofilm to the bottom of the electrode-biofilm. We attribute the current loss at the microelectrode-biofilm to exposure to local microscale conditions that reduced the ability of the microelectrode-biofilm to participate in extracellular electron transfer. It is possible that such microscale gradients as pH, redox and acetate caused a 30% current drop between top and bottom. Electrochemically active biofilms (EABs) are a specific subset of biofilms that participate in extracellular electron transfer to and from a solid, conductive surface.1 Starting from initial cell attachment, the colonizing cells multiply to take advantage of the solid electron acceptor and eventually form thicker, mature biofilms with cells spatially distributed in the xy-plane (parallel to the surface) and by depth. Typically, extracellular electron transfer is described as occurring through three generic mechanisms: electron shuttling, 1 electron hopping, 2 and metallic-like conductivity.3 Extracellular electron transfer to and from electrodes is generally studied using strains of Shewanella oneidensis and Geobacter sulfurreducens. Although the extracellular electron transfer mechanism may vary among EABs, diffusion and mass transfer processes must also be accounted for. 4 In thicker, mature EABs, diffusion coefficients inside the biofilm have been shown to deviate noticeably from the bulk diffusion coefficients. 5,6 Many techniques exist that can directly measure the microscale physicochemical gradients within live EABs and in biofilms in general.6-11 However, there are comparatively few techniques that directly measure electrochemical gradients within live EABs; these are generally optical-based methods tracking the redox state of c-type cytochromes.12,13 Recently, we used an amperometric microelectrode to enrich microbes locally within a complex microbial mat system that could harness a polarized microelectrode using extracellular electron transfer.14 Because of this, we explored the possibility that a similar method could be used to measure local current by depth in EABs where a variation in local current would indicate some form of electrochemical interaction and possibly limitation. The method is similar to that in previous split-anode 3 and interdigitated electrode array ...

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pH, redox potential and local biofilm potential microenvironments within Geobacter sulfurreducens biofilms and their roles in electron transfer

Cited by 125 publications

References 45 publications

Changes in Land Use and their Effects on Soil Properties in Huixian Karst Wetland System

Changes in Land Use and their Effects on Soil Properties in Huixian Karst Wetland System

Floc Formation Reduces the pH Stress Experienced by Microorganisms Living in Alkaline Environments

Local Current Variation by Depth inGeobacter SulfurreducensBiofilms

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