scholarly journals Outer Cell Surface Components Essential for Fe(III) Oxide Reduction by Geobacter metallireducens

2012 ◽  
Vol 79 (3) ◽  
pp. 901-907 ◽  
Author(s):  
Jessica A. Smith ◽  
Derek R. Lovley ◽  
Pier-Luc Tremblay
Keyword(s):  
Outer Surface ◽  
Surface Protein ◽  
Transcript Abundance ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Outer Cell ◽  
Gene Transcript ◽  
Oxide Reduction ◽  
Geobacter Metallireducens ◽  
Content Type

ABSTRACTGeobacterspecies are important Fe(III) reducers in a diversity of soils and sediments. Mechanisms for Fe(III) oxide reduction have been studied in detail inGeobacter sulfurreducens, but a number of the most thoroughly studied outer surface components ofG. sulfurreducens, particularlyc-type cytochromes, are not well conserved amongGeobacterspecies. In order to identify cellular components potentially important for Fe(III) oxide reduction inGeobacter metallireducens, gene transcript abundance was compared in cells grown on Fe(III) oxide or soluble Fe(III) citrate with whole-genome microarrays. Outer-surface cytochromes were also identified. Deletion of genes forc-type cytochromes that had higher transcript abundance during growth on Fe(III) oxides and/or were detected in the outer-surface protein fraction identified sixc-type cytochrome genes, that when deleted removed the capacity for Fe(III) oxide reduction. Several of thec-type cytochromes which were essential for Fe(III) oxide reduction inG. metallireducenshave homologs inG. sulfurreducensthat are not important for Fe(III) oxide reduction. Other genes essential for Fe(III) oxide reduction included a gene predicted to encode an NHL (Ncl-1–HT2A–Lin-41) repeat-containing protein and a gene potentially involved in pili glycosylation. Genes associated with flagellum-based motility, chemotaxis, and pili had higher transcript abundance during growth on Fe(III) oxide, consistent with the previously proposed importance of these components in Fe(III) oxide reduction. These results demonstrate that there are similarities in extracellular electron transfer betweenG. metallireducensandG. sulfurreducensbut the outer-surfacec-type cytochromes involved in Fe(III) oxide reduction are different.

scholarly journals The electrically conductive pili of Geobacter soli

2020 ◽  
Author(s):  
Shiyan Zhuo ◽  
Guiqin Yang ◽  
Li Zhuang
Keyword(s):  
Electron Transfer ◽  
Outer Surface ◽  
Electronic Materials ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Oxide Reduction ◽  
Electrically Conductive ◽  
Current Production ◽  
Current Densities ◽  
Pilin Gene

AbstractElectrically conductive pili (e-pili) enable electron transport over multiple cell lengths to extracellular environments and play an important role in extracellular electron transfer (EET) of Geobacter species. To date, the studies of e-pili have mainly focused on Geobacter sulfurreducens and the closely related Geobacter metallireducens because of their developed genetic manipulation systems. We investigated the role of G. soli pili in EET by directly deleting the pilin gene, pilA, which is predicted to encode e-pili. Deletion of pilA, prevented the production of pili, resulting in poor Fe(III) oxide reduction and low current production, implying that G. soli pili is required for EET. To further evaluate the conductivity of G. soli pili compared with G. sulfurreducens pili, the pilA of G. soli was heterologously expressed in G. sulfurreducens, yielding the G. sulfurreducens strain GSP. This strain produced abundant pili with similar conductivity to the control strain that expressed native G. sulfurreducens pili, consistent with G. soli as determined by direct measurement, which suggested that G. soli pili is electrically conductive. Surprisingly, strain GSP was deficient in Fe(III) oxide reduction and current production due to the impaired content of outer-surface c-type cytochromes. These results demonstrated that heterologous pili of G. sulfurreducens severely reduces the content of outer-surface c-type cytochromes and consequently eliminates the capacity for EET, which strongly suggests an attention should be paid to the content of c-type cytochromes when employing G. sulfurreducens to heterologously express pili from other microorganisms.IMPORTANCEThe studies of electrically conductive pili (e-pili) of Geobacter species are of interest because of its application prospects in electronic materials. e-Pili are considered a substitution for electronic materials due to its renewability, biodegradability and robustness. Continued exploration of additional e-pili of Geobacter soli will improve the understanding of their biological role in extracellular electron transfer and expand the range of available electronic materials. Heterologously expressing the pilin genes from phylogenetically diverse microorganisms has been proposed as an emerging approach to screen potential e-pili according to high current densities. However, our results indicated that a Geobacter sulfurreducens strain heterologously expressing a pilin gene produced low current densities that resulted from a lack of content of c-type cytochromes, which were likely to possess e-pili. These results provide referential significance to yield e-pili from diverse microorganisms.

scholarly journals Transcriptomic and Genetic Analysis of Direct Interspecies Electron Transfer

2013 ◽  
Vol 79 (7) ◽  
pp. 2397-2404 ◽  
Author(s):  
Pravin Malla Shrestha ◽  
Amelia-Elena Rotaru ◽  
Zarath M. Summers ◽  
Minita Shrestha ◽  
Fanghua Liu ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Expression Patterns ◽  
Transcript Abundance ◽  
Geobacter Sulfurreducens ◽  
Acetate Metabolism ◽  
Gene Transcript ◽  
Content Type ◽  
Direct Interspecies Electron Transfer ◽  
Interspecies Electron Transfer ◽  
Pilin Gene

ABSTRACTThe possibility that metatranscriptomic analysis could distinguish between direct interspecies electron transfer (DIET) and H2interspecies transfer (HIT) in anaerobic communities was investigated by comparing gene transcript abundance in cocultures in whichGeobacter sulfurreducenswas the electron-accepting partner for eitherGeobacter metallireducens, which performs DIET, orPelobacter carbinolicus, which relies on HIT. Transcript abundance forG. sulfurreducensuptake hydrogenase genes was 7-fold lower in cocultures withG. metallireducensthan in cocultures withP. carbinolicus, consistent with DIET and HIT, respectively, in the two cocultures. Transcript abundance for the pilus-associated cytochrome OmcS, which is essential for DIET but not for HIT, was 240-fold higher in the cocultures withG. metallireducensthan in cocultures withP. carbinolicus. The pilin genepilAwas moderately expressed despite a mutation that might be expected to represspilAexpression. Lower transcript abundance forG. sulfurreducensgenes associated with acetate metabolism in the cocultures withP. carbinolicuswas consistent with the repression of these genes by H2during HIT. Genes for the biogenesis of pili and flagella and severalc-type cytochrome genes were among the most highly expressed inG. metallireducens. Mutant strains that lacked the ability to produce pili, flagella, or the outer surfacec-type cytochrome encoded by Gmet_2896 were not able to form cocultures withG. sulfurreducens. These results demonstrate that there are unique gene expression patterns that distinguish DIET from HIT and suggest that metatranscriptomics may be a promising route to investigate interspecies electron transfer pathways in more-complex environments.

scholarly journals U(VI) Reduction by Diverse Outer Surfacec-Type Cytochromes of Geobacter sulfurreducens

2013 ◽  
Vol 79 (20) ◽  
pp. 6369-6374 ◽  
Author(s):  
Roberto Orellana ◽  
Janet J. Leavitt ◽  
Luis R. Comolli ◽  
Roseann Csencsits ◽  
Noemie Janot ◽  
...  
Keyword(s):  
Outer Surface ◽  
Geobacter Sulfurreducens ◽  
Outer Cell ◽  
Wild Type ◽  
Energy Dispersion Spectroscopy ◽  
Edge Structure ◽  
Content Type ◽  
X Ray ◽  
Transmission Electron ◽  
Pilin Protein

ABSTRACTEarly studies withGeobacter sulfurreducenssuggested that outer-surfacec-type cytochromes might play a role in U(VI) reduction, but it has recently been suggested that there is substantial U(VI) reduction at the surface of the electrically conductive pili known as microbial nanowires. This phenomenon was further investigated. A strain ofG. sulfurreducens, known as Aro-5, which produces pili with substantially reduced conductivity reduced U(VI) nearly as well as the wild type, as did a strain in which the gene for PilA, the structural pilin protein, was deleted. In order to reduce rates of U(VI) reduction to levels less than 20% of the wild-type rates, it was necessary to delete the genes for the five most abundant outer surfacec-type cytochromes ofG. sulfurreducens. X-ray absorption near-edge structure spectroscopy demonstrated that whereas 83% ± 10% of the uranium associated with wild-type cells correspond to U(IV) after 4 h of incubation, with the quintuple mutant, 89% ± 10% of uranium was U(VI). Transmission electron microscopy and X-ray energy dispersion spectroscopy revealed that wild-type cells did not precipitate uranium along pili as previously reported, but U(IV) was precipitated at the outer cell surface. These findings are consistent with those of previous studies, which have suggested thatG. sulfurreducensrequires outer-surfacec-type cytochromes but not pili for the reduction of soluble extracellular electron acceptors.

scholarly journals Simultaneous Catabolism of Plant-Derived Aromatic Compounds Results in Enhanced Growth for Members of the Roseobacter Lineage

2013 ◽  
Vol 79 (12) ◽  
pp. 3716-3723 ◽  
Author(s):  
Christopher A. Gulvik ◽  
Alison Buchan
Keyword(s):  
Salt Marshes ◽  
Aromatic Compounds ◽  
Soil Bacteria ◽  
Transcript Abundance ◽  
Gene Transcript ◽  
Content Type ◽  
Coastal Salt Marshes ◽  
Metabolic Versatility ◽  
Organic Carbon Pool ◽  
Ruegeria Pomeroyi

ABSTRACTPlant-derived aromatic compounds are important components of the dissolved organic carbon pool in coastal salt marshes, and their mineralization by resident bacteria contributes to carbon cycling in these systems. Members of the roseobacter lineage of marine bacteria are abundant in coastal salt marshes, and several characterized strains, includingSagittula stellataE-37, utilize aromatic compounds as primary growth substrates. The genome sequence ofS. stellatacontains multiple, potentially competing, aerobic ring-cleaving pathways. Preferential hierarchies in substrate utilization and complex transcriptional regulation have been demonstrated to be the norm in many soil bacteria that also contain multiple ring-cleaving pathways. The purpose of this study was to ascertain whether substrate preference exists inS. stellatawhen the organism is provided a mixture of aromatic compounds that proceed through different ring-cleaving pathways. We focused on the protocatechuate (pca) and the aerobic benzoyl coenzyme A (box) pathways and the substrates known to proceed through them,p-hydroxybenzoate (POB) and benzoate, respectively. When these two substrates were provided at nonlimiting carbon concentrations, temporal patterns of cell density, gene transcript abundance, enzyme activity, and substrate concentrations indicated thatS. stellatasimultaneously catabolized both substrates. Furthermore, enhanced growth rates were observed whenS. stellatawas provided both compounds simultaneously compared to the rates of cells grown singly with an equimolar concentration of either substrate alone. This simultaneous-catabolism phenotype was also demonstrated in another lineage member,Ruegeria pomeroyiDSS-3. These findings challenge the paradigm of sequential aromatic catabolism reported for soil bacteria and contribute to the growing body of physiological evidence demonstrating the metabolic versatility of roseobacters.

scholarly journals Nitrogen Utilization and Metabolism in Ruminococcus albus 8

2014 ◽  
Vol 80 (10) ◽  
pp. 3095-3102 ◽  
Author(s):  
Jong Nam Kim ◽  
Emily DeCrescenzo Henriksen ◽  
Isaac K. O. Cann ◽  
Roderick I. Mackie
Keyword(s):  
Growth Rate ◽  
Nitrogen Source ◽  
Nitrogen Metabolism ◽  
Enzyme Activities ◽  
Transcript Abundance ◽  
Gene Transcript ◽  
Sole Nitrogen Source ◽  
Ruminococcus Albus ◽  
Content Type ◽  
Maximum Cell

ABSTRACTThe model rumenFirmicutesorganismRuminococcus albus8 was grown using ammonia, urea, or peptides as the sole nitrogen source; growth was not observed with amino acids as the sole nitrogen source. Growth ofR. albus8 on ammonia and urea showed the same growth rate (0.08 h−1) and similar maximum cell densities (for ammonia, the optical density at 600 nm [OD600] was 1.01; and for urea, the OD600was 0.99); however, growth on peptides resulted in a nearly identical growth rate (0.09 h−1) and a lower maximum cell density (OD600= 0.58). To identify differences in gene expression and enzyme activities, the transcript abundances of 10 different genes involved in nitrogen metabolism and specific enzyme activities were analyzed by harvesting mRNA and crude protein from cells at the mid- and late exponential phases of growth on the different N sources. Transcript abundances and enzyme activities varied according to nitrogen source, ammonia concentration, and growth phase. Growth ofR. albus8 on ammonia and urea was similar, with the only observed difference being an increase in urease transcript abundance and enzyme activity in urea-grown cultures. Growth ofR. albus8 on peptides showed a different nitrogen metabolism pattern, with higher gene transcript abundance levels ofgdhA,glnA,gltB,amtB,glnK, andureC, as well as higher activities of glutamate dehydrogenase and urease. These results demonstrate that ammonia, urea, and peptides can all serve as nitrogen sources forR. albusand that nitrogen metabolism genes and enzyme activities ofR. albus8 are regulated by nitrogen source and the level of ammonia in the growth medium.

scholarly journals A Geobacter sulfurreducens Strain Expressing Pseudomonas aeruginosa Type IV Pili Localizes OmcS on Pili but Is Deficient in Fe(III) Oxide Reduction and Current Production

2013 ◽  
Vol 80 (3) ◽  
pp. 1219-1224 ◽  
Author(s):  
Xing Liu ◽  
Pier-Luc Tremblay ◽  
Nikhil S. Malvankar ◽  
Kelly P. Nevin ◽  
Derek R. Lovley ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Electron Transfer ◽  
Structural Features ◽  
Geobacter Sulfurreducens ◽  
Control Strain ◽  
Oxide Reduction ◽  
Content Type ◽  
Type Iv ◽  
Current Production ◽  
Pilin Protein

ABSTRACTThe conductive pili ofGeobacterspecies play an important role in electron transfer to Fe(III) oxides, in long-range electron transport through current-producing biofilms, and in direct interspecies electron transfer. Although multiple lines of evidence have indicated that the pili ofGeobacter sulfurreducenshave a metal-like conductivity, independent of the presence ofc-type cytochromes, this claim is still controversial. In order to further investigate this phenomenon, a strain ofG. sulfurreducens, designated strain PA, was constructed in which the gene for the native PilA, the structural pilin protein, was replaced with the PilA gene ofPseudomonas aeruginosaPAO1. Strain PA expressed and properly assembledP. aeruginosaPilA subunits into pili and exhibited a profile of outer surfacec-type cytochromes similar to that of a control strain expressing theG. sulfurreducensPilA. Surprisingly, the strain PA pili were decorated with thec-type cytochrome OmcS in a manner similar to the control strain. However, the strain PA pili were 14-fold less conductive than the pili of the control strain, and strain PA was severely impaired in Fe(III) oxide reduction and current production. These results demonstrate that the presence of OmcS on pili is not sufficient to confer conductivity to pili and suggest that there are unique structural features of theG. sulfurreducensPilA that are necessary for conductivity.

scholarly journals Anaerobic Benzene Oxidation via Phenol in Geobacter metallireducens

2013 ◽  
Vol 79 (24) ◽  
pp. 7800-7806 ◽  
Author(s):  
Tian Zhang ◽  
Pier-Luc Tremblay ◽  
Akhilesh Kumar Chaurasia ◽  
Jessica A. Smith ◽  
Timothy S. Bain ◽  
...  
Keyword(s):  
Expression Patterns ◽  
Geobacter Sulfurreducens ◽  
Environmental Significance ◽  
Geobacter Metallireducens ◽  
Content Type ◽  
Benzene Degradation ◽  
Metabolic Route ◽  
Benzene Hydroxylation ◽  
Anaerobic Benzene Degradation ◽  
Anaerobic Conversion

ABSTRACTAnaerobic activation of benzene is expected to represent a novel biochemistry of environmental significance. Therefore, benzene metabolism was investigated inGeobacter metallireducens, the only genetically tractable organism known to anaerobically degrade benzene. Trace amounts (<0.5 μM) of phenol accumulated in cultures ofGeobacter metallireducensanaerobically oxidizing benzene to carbon dioxide with the reduction of Fe(III). Phenol was not detected in cell-free controls or in Fe(II)- and benzene-containing cultures ofGeobacter sulfurreducens, aGeobacterspecies that cannot metabolize benzene. The phenol produced inG. metallireducenscultures was labeled with18O during growth in H218O, as expected for anaerobic conversion of benzene to phenol. Analysis of whole-genome gene expression patterns indicated that genes for phenol metabolism were upregulated during growth on benzene but that genes for benzoate or toluene metabolism were not, further suggesting that phenol was an intermediate in benzene metabolism. Deletion of the genes for PpsA or PpcB, subunits of two enzymes specifically required for the metabolism of phenol, removed the capacity for benzene metabolism. These results demonstrate that benzene hydroxylation to phenol is an alternative to carboxylation for anaerobic benzene activation and suggest that this may be an important metabolic route for benzene removal in petroleum-contaminated groundwaters, in whichGeobacterspecies are considered to play an important role in anaerobic benzene degradation.

scholarly journals Adaptive Evolution of Geobacter sulfurreducens in Coculture with Pseudomonas aeruginosa

mBio ◽  
2020 ◽  
Vol 11 (2) ◽  
Author(s):  
Lucie Semenec ◽  
Ismael A. Vergara ◽  
Andrew E. Laloo ◽  
Steve Petrovski ◽  
Philip L. Bond ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Electron Transfer ◽  
Adaptive Evolution ◽  
Efflux Pump ◽  
Antibiotic Production ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Content Type ◽  
Interaction Dynamics ◽  
Syntrophic Interaction

ABSTRACT Interactions between microorganisms in mixed communities are highly complex, being either syntrophic, neutral, predatory, or competitive. Evolutionary changes can occur in the interaction dynamics between community members as they adapt to coexistence. Here, we report that the syntrophic interaction between Geobacter sulfurreducens and Pseudomonas aeruginosa coculture change in their dynamics over evolutionary time. Specifically, Geobacter sp. dominance increases with adaptation within the cocultures, as determined through quantitative PCR and fluorescence in situ hybridization. This suggests a transition from syntrophy to competition and demonstrates the rapid adaptive capacity of Geobacter spp. to dominate in cocultures with P. aeruginosa. Early in coculture establishment, two single-nucleotide variants in the G. sulfurreducens fabI and tetR genes emerged that were strongly selected for throughout coculture evolution with P. aeruginosa phenazine wild-type and phenazine-deficient mutants. Sequential window acquisition of all theoretical spectra-mass spectrometry (SWATH-MS) proteomics revealed that the tetR variant cooccurred with the upregulation of an adenylate cyclase transporter, CyaE, and a resistance-nodulation-division (RND) efflux pump notably known for antibiotic efflux. To determine whether antibiotic production was driving the increased expression of the multidrug efflux pump, we tested Pseudomonas-derived phenazine-1-carboxylic acid (PHZ-1-CA) for its potential to inhibit Geobacter growth and drive selection of the tetR and fabI genetic variants. Despite its inhibitory properties, PHZ-1-CA did not drive variant selection, indicating that other antibiotics may drive overexpression of the efflux pump and CyaE or that a novel role exists for these proteins in the context of this interaction. IMPORTANCE Geobacter and Pseudomonas spp. cohabit many of the same environments, where Geobacter spp. often dominate. Both bacteria are capable of extracellular electron transfer (EET) and play important roles in biogeochemical cycling. Although they recently in 2017 were demonstrated to undergo direct interspecies electron transfer (DIET) with one another, the genetic evolution of this syntrophic interaction has not been examined. Here, we use whole-genome sequencing of the cocultures before and after adaptive evolution to determine whether genetic selection is occurring. We also probe their interaction on a temporal level and determine whether their interaction dynamics change over the course of adaptive evolution. This study brings to light the multifaceted nature of interactions between just two microorganisms within a controlled environment and will aid in improving metabolic models of microbial communities comprising these two bacteria.

scholarly journals Extracellular Electron Transfer: Respiratory or Nutrient Homeostasis?

2020 ◽  
Vol 202 (7) ◽  
Author(s):  
Lars J. C. Jeuken ◽  
Kiel Hards ◽  
Yoshio Nakatani
Keyword(s):  
Electron Transfer ◽  
Iron Reduction ◽  
Ferric Iron ◽  
Shewanella Oneidensis ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Gram Positive ◽  
Content Type ◽  
Gram Positive Bacteria ◽  
Nutrient Homeostasis

ABSTRACT Exoelectrogens are able to transfer electrons extracellularly, enabling them to respire on insoluble terminal electron acceptors. Extensively studied exoelectrogens, such as Geobacter sulfurreducens and Shewanella oneidensis, are Gram negative. More recently, it has been reported that Gram-positive bacteria, such as Listeria monocytogenes and Enterococcus faecalis, also exhibit the ability to transfer electrons extracellularly, although it is still unclear whether this has a function in respiration or in redox control of the environment, for instance, by reducing ferric iron for iron uptake. In this issue of Journal of Bacteriology, Hederstedt and colleagues report on experiments that directly compare extracellular electron transfer (EET) pathways for ferric iron reduction and respiration and find a clear difference (L. Hederstedt, L. Gorton, and G. Pankratova, J Bacteriol 202:e00725-19, 2020, https://doi.org/10.1128/JB.00725-19), providing further insights and new questions into the function and metabolic pathways of EET in Gram-positive bacteria.

scholarly journals A New Approach for Evaluating Electron Transfer Dynamics by Using In Situ Resonance Raman Microscopy and Chronoamperometry in Conjunction with a Dynamic Model

2020 ◽  
Vol 86 (20) ◽  
Author(s):  
Adolf Krige ◽  
Kerstin Ramser ◽  
Magnus Sjöblom ◽  
Paul Christakopoulos ◽  
Ulrika Rova
Keyword(s):  
Electron Transfer ◽  
Dynamic Model ◽  
Oxidation Rate ◽  
Resonance Raman ◽  
Raman Microscopy ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Current Response ◽  
Content Type ◽  
Raman Response

ABSTRACT Geobacter sulfurreducens is a good candidate as a chassis organism due to its ability to form thick, conductive biofilms, enabling long-distance extracellular electron transfer (EET). Due to the complexity of EET pathways in G. sulfurreducens, a dynamic approach is required to study genetically modified EET rates in the biofilm. By coupling online resonance Raman microscopy with chronoamperometry, we were able to observe the dynamic discharge response in the biofilm’s cytochromes to an increase in anode voltage. Measuring the heme redox state alongside the current allows for the fitting of a dynamic model using the current response and a subsequent validation of the model via the value of a reduced cytochrome c Raman peak. The modeled reduced cytochromes closely fitted the Raman response data from the G. sulfurreducens wild-type strain, showing the oxidation of heme groups in cytochromes until a new steady state was achieved. Furthermore, the use of a dynamic model also allows for the calculation of internal rates, such as acetate and NADH consumption rates. The Raman response of a mutant lacking OmcS showed a higher initial oxidation rate than predicted, followed by an almost linear decrease of the reduced mediators. The increased initial rate could be attributed to an increase in biofilm conductivity, previously observed in biofilms lacking OmcS. One explanation for this is that OmcS acts as a conduit between cytochromes; therefore, deleting the gene restricts the rate of electron transfer to the extracellular matrix. This could, however, be modeled assuming a linear oxidation rate of intercellular mediators. IMPORTANCE Bioelectrochemical systems can fill a vast array of application niches, due to the control of redox reactions that it offers. Although native microorganisms are preferred for applications such as bioremediation, more control is required for applications such as biosensors or biocomputing. The development of a chassis organism, in which the EET is well defined and readily controllable, is therefore essential. The combined approach in this work offers a unique way of monitoring and describing the reaction kinetics of a G. sulfurreducens biofilm, as well as offering a dynamic model that can be used in conjunction with applications such as biosensors.

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