Memristive devices are promising candidates to emulate biological computing. However, the typical switching voltages (0.2-2 V) in previously described devices are much higher than the amplitude in ...biological counterparts. Here we demonstrate a type of diffusive memristor, fabricated from the protein nanowires harvested from the bacterium Geobacter sulfurreducens, that functions at the biological voltages of 40-100 mV. Memristive function at biological voltages is possible because the protein nanowires catalyze metallization. Artificial neurons built from these memristors not only function at biological action potentials (e.g., 100 mV, 1 ms) but also exhibit temporal integration close to that in biological neurons. The potential of using the memristor to directly process biosensing signals is also demonstrated.
The possibility that
(formerly
) and
species cooperate via direct interspecies electron transfer (DIET) in terrestrial methanogenic environments was investigated in rice paddy soils. Genes with high ...sequence similarity to the gene for the PilA pilin monomer of the electrically conductive pili (e-pili) of
accounted for over half of the PilA gene sequences in metagenomic libraries and 42% of the mRNA transcripts in RNA sequencing (RNA-seq) libraries. This abundance of e-pilin genes and transcripts is significant because e-pili can serve as conduits for DIET. Most of the e-pilin genes and transcripts were affiliated with
species, but sequences most closely related to putative e-pilin genes from genera such as
,
,
, and
, were also detected. Approximately 17% of all metagenomic and metatranscriptomic bacterial sequences clustered with
species, and the finding that
spp. were actively transcribing growth-related genes indicated that they were metabolically active in the soils. Genes coding for e-pilin were among the most highly transcribed
genes. In addition, homologs of genes encoding OmcS, a
-type cytochrome associated with the e-pili of
and required for DIET, were also highly expressed in the soils.
species in the soils highly expressed genes for enzymes involved in the reduction of carbon dioxide to methane. DIET is the only electron donor known to support CO
reduction in
Thus, these results are consistent with a model in which
species were providing electrons to
species for methane production through electrical connections of e-pili.
species are some of the most important microbial contributors to global methane production, but surprisingly little is known about their physiology and ecology. The possibility that DIET is a source of electrons for
in methanogenic rice paddy soils is important because it demonstrates that the contribution that
makes to methane production in terrestrial environments may extend beyond the conversion of acetate to methane. Furthermore, defined coculture studies have suggested that when
species receive some of their energy from DIET, they grow faster than when acetate is their sole energy source. Thus,
growth and metabolism in methanogenic soils may be faster and more robust than generally considered. The results also suggest that the reason that
species are repeatedly found to be among the most metabolically active microorganisms in methanogenic soils is that they grow syntrophically in cooperation with
spp., and possibly other methanogens, via DIET.
Geobacter Protein Nanowires Lovley, Derek R.; Walker, David J. F.
Frontiers in microbiology,
09/2019, Volume:
10
Journal Article
Peer reviewed
Open access
The study of electrically conductive protein nanowires in
Geobacter sulfurreducens
has led to new concepts for long-range extracellular electron transport, as well as for the development of ...sustainable conductive materials and electronic devices with novel functions. Until recently, electrically conductive pili (e-pili), assembled from the PilA pilin monomer, were the only known
Geobacter
protein nanowires. However, filaments comprised of the multi-heme
c
-type cytochrome, OmcS, are present in some preparations of
G. sulfurreducens
outer-surface proteins. The purpose of this review is to evaluate the available evidence on the
in vivo
expression of e-pili and OmcS filaments and their biological function. Abundant literature demonstrates that
G. sulfurreducens
expresses e-pili, which are required for long-range electron transport to Fe (III) oxides and through conductive biofilms. In contrast, there is no definitive evidence yet that wild-type
G. sulfurreducens
express long filaments of OmcS extending from the cells, and deleting the gene for OmcS actually
increases
biofilm conductivity. The literature does not support the concern that many previous studies on e-pili were mistakenly studying OmcS filaments. For example, heterologous expression of the aromatic-rich pilin monomer of
Geobacter metallireducens
in
G. sulfurreducens
increases the conductivity of individual nanowires more than 5,000-fold, whereas expression of an aromatic-poor pilin reduced conductivity more than 1,000-fold. This more than million-fold range in nanowire conductivity was achieved while maintaining the 3-nm diameter characteristic of e-pili. Purification methods that eliminate all traces of OmcS yield highly conductive e-pili, as does heterologous expression of the e-pilin monomer in microbes that do not produce OmcS or any other outer-surface cytochromes. Future studies of
G. sulfurreducens
expression of protein nanowires need to be cognizant of the importance of maintaining environmentally relevant growth conditions because artificial laboratory culture conditions can rapidly select against e-pili expression. Principles derived from the study of e-pili have enabled identification of non-cytochrome protein nanowires in diverse bacteria and archaea. A similar search for cytochrome appendages is warranted. Both e-pili and OmcS filaments offer design options for the synthesis of protein-based “green” electronics, which may be the primary driving force for the study of these structures in the near future.
A multidisciplinary panel of 18 physicians and 3 non-physicians from eight countries (Sweden, UK, Argentina, Australia, Italy, Finland, Norway and the USA) reviewed the literature on diagnosis and ...management of adult coeliac disease (CD). This paper presents the recommendations of the British Society of Gastroenterology. Areas of controversies were explored through phone meetings and web surveys. Nine working groups examined the following areas of CD diagnosis and management: classification of CD; genetics and immunology; diagnostics; serology and endoscopy; follow-up; gluten-free diet; refractory CD and malignancies; quality of life; novel treatments; patient support; and screening for CD.
Syntrophic interspecies electron exchange is essential for the stable functioning of diverse anaerobic microbial communities. Hydrogen/formate interspecies electron transfer (HFIT), in which H
and/or ...formate function as diffusible electron carriers, has been considered to be the primary mechanism for electron transfer because most common syntrophs were thought to lack biochemical components, such as electrically conductive pili (e-pili), necessary for direct interspecies electron transfer (DIET). Here we report that Syntrophus aciditrophicus, one of the most intensively studied microbial models for HFIT, produces e-pili and can grow via DIET. Heterologous expression of the putative S. aciditrophicus type IV pilin gene in Geobacter sulfurreducens yielded conductive pili of the same diameter (4 nm) and conductance of the native S. aciditrophicus pili and enabled long-range electron transport in G. sulfurreducens. S. aciditrophicus lacked abundant c-type cytochromes often associated with DIET. Pilin genes likely to yield e-pili were found in other genera of hydrogen/formate-producing syntrophs. The finding that DIET is a likely option for diverse syntrophs that are abundant in many anaerobic environments necessitates a reexamination of the paradigm that HFIT is the predominant mechanism for syntrophic electron exchange within anaerobic microbial communities of biogeochemical and practical significance.
Geobacter sulfurreducens is a model microbe for elucidating the mechanisms for extracellular electron transfer in several biogeochemical cycles, bioelectrochemical applications, and microbial metal ...corrosion. Multiple lines of evidence previously suggested that electrically conductive pili (e-pili) are an essential conduit for long-range extracellular electron transport in G. sulfurreducens. However, it has recently been reported that G. sulfurreducens does not express e-pili and that filaments comprised of multi-heme
-type cytochromes are responsible for long-range electron transport. This possibility was directly investigated by examining cells, rather than filament preparations, with atomic force microscopy. Approximately 90% of the filaments emanating from wild-type cells had a diameter (3 nm) and conductance consistent with previous reports of e-pili harvested from G. sulfurreducens or heterologously expressed in Escherichia coli from the G. sulfurreducens pilin gene. The remaining 10% of filaments had a morphology consistent with filaments comprised of the
-type cytochrome OmcS. A strain expressing a modified pilin gene designed to yield poorly conductive pili expressed 90% filaments with a 3-nm diameter, but greatly reduced conductance, further indicating that the 3-nm diameter conductive filaments in the wild-type strain were e-pili. A strain in which genes for five of the most abundant outer-surface
-type cytochromes, including OmcS, were deleted yielded only 3-nm-diameter filaments with the same conductance as in the wild type. These results demonstrate that e-pili are the most abundant conductive filaments expressed by G. sulfurreducens, consistent with previous functional studies demonstrating the need for e-pili for long-range extracellular electron transfer.
Electroactive microbes have significant environmental impacts, as well as applications in bioenergy and bioremediation. The composition, function, and even existence of electrically conductive pili (e-pili) has been one of the most contentious areas of investigation in electromicrobiology, in part because e-pili offer a mechanism for long-range electron transport that does not involve the metal cofactors common in much of biological electron transport. This study demonstrates that e-pili are abundant filaments emanating from Geobacter sulfurreducens, which serves as a model for long-range extracellular electron transfer in direct interspecies electron transfer, dissimilatory metal reduction, microbe-electrode exchange, and corrosion caused by direct electron uptake from Fe(0). The methods described in this study provide a simple strategy for evaluating the distribution of conductive filaments throughout the microbial world with an approach that avoids artifactual production and/or enrichment of filaments that may not be physiologically relevant.
Microbially produced electrically conductive protein filaments are of interest because they can function as conduits for long-range biological electron transfer. They also show promise as sustainably ...produced electronic materials. Until now, microbially produced conductive protein filaments have been reported only for bacteria. We report here that the archaellum of
is electrically conductive. This is the first demonstration that electrically conductive protein filaments have evolved in
Furthermore, the structure of the
archaellum was previously determined (N. Poweleit, P. Ge, H. N. Nguyen, R. R. O. Loo, et al., Nat Microbiol 2:16222, 2016, https://doi.org/10.1038/nmicrobiol.2016.222). Thus, the archaellum of
is the first microbially produced electrically conductive protein filament for which a structure is known. We analyzed the previously published structure and identified a core of tightly packed phenylalanines that is one likely route for electron conductance. The availability of the
archaellum structure is expected to substantially advance mechanistic evaluation of long-range electron transport in microbially produced electrically conductive filaments and to aid in the design of "green" electronic materials that can be microbially produced with renewable feedstocks.
Microbially produced electrically conductive protein filaments are a revolutionary, sustainably produced, electronic material with broad potential applications. The design of new protein nanowires based on the known
archaellum structure could be a major advance over the current empirical design of synthetic protein nanowires from electrically conductive bacterial pili. An understanding of the diversity of outer-surface protein structures capable of electron transfer is important for developing models for microbial electrical communication with other cells and minerals in natural anaerobic environments. Extracellular electron exchange is also essential in engineered environments such as bioelectrochemical devices and anaerobic digesters converting wastes to methane. The finding that the archaellum of
is electrically conductive suggests that some archaea might be able to make long-range electrical connections with their external environment.
The possibility that bacteria other than Geobacter species might contain genes for electrically conductive pili (e-pili) was investigated by heterologously expressing pilin genes of interest in ...Geobacter sulfurreducens. Strains of G. sulfurreducens producing high current densities, which are only possible with e-pili, were obtained with pilin genes from Flexistipes sinusarabici, Calditerrivibrio nitroreducens and Desulfurivibrio alkaliphilus. The conductance of pili from these strains was comparable to native G. sulfurreducens e-pili. The e-pili derived from C. nitroreducens, and D. alkaliphilus pilin genes are the first examples of relatively long (>100 amino acids) pilin monomers assembling into e-pili. The pilin gene from Candidatus Desulfofervidus auxilii did not yield e-pili, suggesting that the hypothesis that this sulfate reducer wires itself with e-pili to methane-oxidizing archaea to enable anaerobic methane oxidation should be reevaluated. A high density of aromatic amino acids and a lack of substantial aromatic-free gaps along the length of long pilins may be important characteristics leading to e-pili. This study demonstrates a simple method to screen pilin genes from difficult-to-culture microorganisms for their potential to yield e-pili; reveals new sources for biologically based electronic materials; and suggests that a wide phylogenetic diversity of microorganisms may use e-pili for extracellular electron exchange.
The multi-heme
-type cytochrome OmcS is one of the central components used for extracellular electron transport in the Geobacter sulfurreducens strain DL-1, but its role in other microbes, including ...other strains of G. sulfurreducens, is currently a matter of debate. Therefore, we investigated the function of OmcS in the G. sulfurreducens strain KN400, which is even more effective in extracellular electron transfer than the DL-1 strain. We found that deleting
from strain KN400 did not negatively impact the rate of Fe(III) oxide reduction and that the cells expressed conductive filaments. Replacing the wild-type pilin gene with the
pilin gene eliminated the OmcS-deficient strain's ability to transport electrons to insoluble electron acceptors and diminished filament conductivity. These results are consistent with the concept that electrically conductive pili are the primary conduit for long-range electron transfer in G. sulfurreducens and closely related species. These findings, coupled with the lack of OmcS homologs in other microbes capable of extracellular electron transfer, suggest that OmcS is not a common critical component for extracellular electron transfer.
OmcS has been widely studied and noted to be one of the key components for extracellular electron exchange by the Geobacter sulfurreducens strain DL-1. However, the true importance of OmcS warrants further investigation because it is well known that few bacteria, even within the Geobacteraceae family, contain OmcS homologs, and many bacteria that are capable of extracellular electron transfer lack an abundance of any type of outer surface
-type cytochrome. In addition, there is debate about the importance of OmcS filaments in the mechanism of extracellular electron transport to insoluble electron acceptors by G. sulfurreducens. It has been suggested that filaments comprised of OmcS rather than e-pili are the predominant conductive filaments expressed by G. sulfurreducens. However, the results presented here, along with multiple other sources of evidence, indicate that OmcS filaments cannot be the primary, conductive, protein nanowires expressed by G. sulfurreducens.
The literature suggests a lack of consensus on the use of terms related to coeliac disease (CD) and gluten.
A multidisciplinary task force of 16 physicians from seven countries used the electronic ...database PubMed to review the literature for CD-related terms up to January 2011. Teams of physicians then suggested a definition for each term, followed by feedback of these definitions through a web survey on definitions, discussions during a meeting in Oslo and phone conferences. In addition to 'CD', the following descriptors of CD were evaluated (in alphabetical order): asymptomatic, atypical, classical, latent, non-classical, overt, paediatric classical, potential, refractory, silent, subclinical, symptomatic, typical, CD serology, CD autoimmunity, genetically at risk of CD, dermatitis herpetiformis, gluten, gluten ataxia, gluten intolerance, gluten sensitivity and gliadin-specific antibodies.
CD was defined as 'a chronic small intestinal immune-mediated enteropathy precipitated by exposure to dietary gluten in genetically predisposed individuals'. Classical CD was defined as 'CD presenting with signs and symptoms of malabsorption. Diarrhoea, steatorrhoea, weight loss or growth failure is required.' 'Gluten-related disorders' is the suggested umbrella term for all diseases triggered by gluten and the term gluten intolerance should not to be used. Other definitions are presented in the paper.
This paper presents the Oslo definitions for CD-related terms.
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