Assessment of the microbial community in the cathode compartment of a plant microbial fuel cell

Introduction: In plant microbial fuel cells (plant-MFCs) living plants and microorganisms form an electrochemical unit able to produce clean and sustainable electricity from solar energy. It is reasonable to assume that besides the bacteria in the anode compartment also the cathode compartment plays a crucial role for a stable high current producing plant-MFC. In this study we aim to identify dominant bacterial species in the cathode compartment of the plant-MFC

In situ Lokalisierung, PGPR-Effekt und Regulation des ipdC-Gens der Azospirillum brasilense Stämme Sp7 und Sp245 bei verschiedenen Weizensorten, sowie endophytische Kolonisierung durch Herbaspirillum sp. N3

The aim of this PhD thesis was to examine the endophytic colonization behavior of Azospirillum brasilense and Herbaspirillum sp. N3 on wheat roots. The application of the FISH method using species specific phylogenetic oligonucleotide probes and GFP tagging facilitated the detection of a differential colonization behavior by the A. brasilense strains Sp7 and Sp245 on three different wheat varieties (Triticum aestivum). For this purpose a confocal laser scanning microscope (CLSM) was used, which enabled three-dimesional analysis of bacterial colonization of the root. Especially GFP tagged strains were well suited for this application, as there was no pretreatment or sectioning of the root sample necessary. Strain Sp7 was only located on the root surface of all wheat cultivars, whereas strain Sp245 was also found inter- and intracellulary in the outer root cortex layers. There was no recognizable connection between the growth stimulating effect of the inoculum (PGPR-effect) and the localization of the bacteria. The most pronounced PGPR-effect could be observed with the Brazilian wheat cultivar, which seemed to gain greatest benefit of its partnership with A. brasilense due to a certain adaptation to the inoculum. As the production of the auxin IAA (indole-3-acetic acid) plays a major role in stimulating plant growth, the expression of the key gene ipdC (indole-3-pyruvate decarboxylase) was examined. For this, several methods were tested to generate a fusion of the ipdC promoter with a gfp or rfp reporter gene. Constructing a translational promoter fusion with the gfp variant mut3 on plasmid level made expression analyses possible. With this method the promoter region of strain Sp7 located directly upstream of the ipdC start codon was found to differ only in a few bases from strain Sp245. But further upstream a region of about 150 bases was identified in strain Sp245, which was missing in strain Sp7. For Sp245 two different fusions were constructed, which contained the Sp245 promoter region homologous to strain Sp7 and the whole promoter region of Sp245, respectively. With these constructs the importance of the promoter region only present in strain Sp245 for control and intensity of ipdC expression in A. brasilense Sp245 could be demonstrated. Additionally an induction of the corresponding ipdC promoter fusions of Sp7 and Sp245 was achieved when adding phenylalanine or tyrosine. Total promoter activity was higher in strain Sp7 than in strain Sp245, and ipdC expression appeared to be subject to a stricter control in strain Sp245. These results were confirmed, when the strains containing the promoter fusions were used as reporters for ipdC expression on wheat roots. A demonstration of the induction of the ipdC promoter by root exudates in situ was possible. Finally, isolate N3 from surface sterilized wheat roots was characterized in detail. According to the 16S rDNA sequence data the isolate was phylogenetically allocated to the genus Herbaspirillum. But a subsequent DNS-DNS hybridization ruled out, that the strain belonged to any of the known Herbaspirillum species. Thus, the isolate, which might represent a new species, was named Herbaspirillum sp. N3. A specific, 16S rRNA targeted probe was constructed, which facilitated the examination of wheat roots colonization by this bacteria using FISH. Additionally the strain was GFP tagged to enable the detection in uncut root material. By this, an unequivocal demonstration of the endophytic colonization by Herbaspirillum sp. N3 mainly within the intercellular spaces was possible.In der vorliegenden Arbeit wurde die endophytische Besiedlung von Weizenwurzeln durch Azospirillum brasilense und Herbaspirillum sp. N3 untersucht. Mittels FISH-Methode mit artspezifischen phylogenetischen Oligonukleotidsonden und GFP-Markierungen konnte bei den A. brasilense Stämmen Sp7 und Sp245 an drei verschiedenen Weizensorten (Triticum aestivum) ein unterschiedliches Besiedlungsverhalten gezeigt werden. Hierzu wurde ein konfokales Laser-Scanning-Mikroskop verwendet, mit dem eine dreidimensionale Aufklärung der bakteriellen Besiedlung der Wurzel möglich war. Für diese Anwendung eigneten sich besonders die GFP-markierten Stämme, da die Detektion in diesem Falle ohne Vorbehandlung oder Schneiden der Wurzel erfolgen konnte. Stamm Sp7 konnte bei allen Kultivaren nur an der Oberfläche lokalisiert werden, während Stamm Sp245 auch inter- und intrazellulär in den äußeren Kortexschichten der Wurzel gefunden wurde. Es war kein Zusammenhang zwischen der wachstumsstimulierenden Wirkung des Inokulums (PGPR-Effekt) und der Lokalisierung der Bakterien nachweisbar. Der stärkste PGPR-Effekt konnte bei dem verwendeten brasilianischen Weizenkultivar dokumentiert werden, das offensichtlich aufgrund einer gewissen Anpassung an das Inokulum den größten Nutzen aus der bakteriellen Besiedlung zu ziehen vermochte. Da für den PGPR-Effekt die Produktion des Auxins IES (Indol-3-Essigsäure) von zentraler Bedeutung ist, wurde die Expression des Schlüsselgens ipdC (Indol-3-pyruvat Decarboxylase) einer genauen Untersuchung unterzogen. Dazu wurden eine Reihe von Methoden getestet, um eine Fusion des ipdC-Promotors mit einem gfp- oder rfp-Reportergen zu erzeugen. Durch die Konstruktion translationaler Promotorfusionen mit der gfp-Variante mut3 auf Plasmidebene waren Expressionsanalysen möglich. Dabei ergab sich, dass sich die unmittelbar strangaufwärts des ipdC-Startcodons gelegene Promotorregionen des Stammes Sp7 nur in wenigen Basen von der des Stammes Sp245 unterscheidet. Allerdings schließt sich strangaufwärts an diesen Bereich bei Stamm Sp245 ein etwa 150 Basenpaare messender Abschnitt an, der bei Stamm Sp7 fehlt. Durch die Konstruktion von zwei verschiedenen Fusionen, die einmal den zu Stamm Sp7 homologen Bereich und einmal die gesamte Promotorregion von Sp245 beinhalteten, konnte eine maßgebliche Bedeutung dieser nur bei Stamm Sp245 vorhandenen Region für Kontrolle und Stärke der ipdC-Expression in A. brasilense Sp245 nachgewiesen werden. Außerdem erfolgte durch die Zugabe von Phenylalanin und Tyrosin eine Induzierung der entsprechenden ipdC-Promotorfusionen bei Sp7 und Sp245. Dabei lag die maximale Promotoraktivität bei Stamm Sp7 höher als bei Stamm Sp245. Bei letzterem unterliegt die ipdC-Expression jedoch einer strengeren Kontrolle. Diese Ergebnisse wurden beim Einsatz der Transkonjuganden als Reporterstämme der ipdC-Expression auf Weizenwurzeln bestätigt. Es konnte eine Induzierbarkeit des ipdC-Promotors durch die Wurzelexsudate in situ nachgewiesen werden. Schließlich wurde das von oberflächensterilisierten Weizenwurzeln gewonnene Isolat N3 einer genaueren Charakterisierung unterzogen. Anhand der 16S rDNS Sequenzdaten ließ sich das Isolat phylogenetisch der Gattung Herbaspirillum zuordnen, wobei eine nachfolgende DNS-DNS-Hybridisierung die Zugehörigkeit zu einer der bekannten Herbaspirillum Spezies ausschloss. Für das demnach als Herbaspirillum sp. N3 bezeichnete Isolat, das möglicherweise den Vertreter einer neuen Art darstellt, wurde eine spezifische, 16S rRNS gerichtete Sonde entwickelt, mit der die Besiedlung von inokulierten Weizensorten durch diesen Bakterienstamm mittels FISH untersucht werden konnte. Außerdem wurde eine GFP-Markierung zur Detektion in ungeschnittenem Wurzelmaterial vorgenommen. Dabei ließ sich eindeutig eine endophytische Besiedlungsweise von Herbaspirillum sp. N3 demonstrieren, wobei das Bakterium bevorzugt in Interzellularräumen der Wurzel lokalisiert war

In situ Lokalisierung, PGPR-Effekt und Regulation des ipdC-Gens der Azospirillum brasilense Stämme Sp7 und Sp245 bei verschiedenen Weizensorten, sowie endophytische Kolonisierung durch Herbaspirillum sp. N3

The aim of this PhD thesis was to examine the endophytic colonization behavior of Azospirillum brasilense and Herbaspirillum sp. N3 on wheat roots. The application of the FISH method using species specific phylogenetic oligonucleotide probes and GFP tagging facilitated the detection of a differential colonization behavior by the A. brasilense strains Sp7 and Sp245 on three different wheat varieties (Triticum aestivum). For this purpose a confocal laser scanning microscope (CLSM) was used, which enabled three-dimesional analysis of bacterial colonization of the root. Especially GFP tagged strains were well suited for this application, as there was no pretreatment or sectioning of the root sample necessary. Strain Sp7 was only located on the root surface of all wheat cultivars, whereas strain Sp245 was also found inter- and intracellulary in the outer root cortex layers. There was no recognizable connection between the growth stimulating effect of the inoculum (PGPR-effect) and the localization of the bacteria. The most pronounced PGPR-effect could be observed with the Brazilian wheat cultivar, which seemed to gain greatest benefit of its partnership with A. brasilense due to a certain adaptation to the inoculum. As the production of the auxin IAA (indole-3-acetic acid) plays a major role in stimulating plant growth, the expression of the key gene ipdC (indole-3-pyruvate decarboxylase) was examined. For this, several methods were tested to generate a fusion of the ipdC promoter with a gfp or rfp reporter gene. Constructing a translational promoter fusion with the gfp variant mut3 on plasmid level made expression analyses possible. With this method the promoter region of strain Sp7 located directly upstream of the ipdC start codon was found to differ only in a few bases from strain Sp245. But further upstream a region of about 150 bases was identified in strain Sp245, which was missing in strain Sp7. For Sp245 two different fusions were constructed, which contained the Sp245 promoter region homologous to strain Sp7 and the whole promoter region of Sp245, respectively. With these constructs the importance of the promoter region only present in strain Sp245 for control and intensity of ipdC expression in A. brasilense Sp245 could be demonstrated. Additionally an induction of the corresponding ipdC promoter fusions of Sp7 and Sp245 was achieved when adding phenylalanine or tyrosine. Total promoter activity was higher in strain Sp7 than in strain Sp245, and ipdC expression appeared to be subject to a stricter control in strain Sp245. These results were confirmed, when the strains containing the promoter fusions were used as reporters for ipdC expression on wheat roots. A demonstration of the induction of the ipdC promoter by root exudates in situ was possible. Finally, isolate N3 from surface sterilized wheat roots was characterized in detail. According to the 16S rDNA sequence data the isolate was phylogenetically allocated to the genus Herbaspirillum. But a subsequent DNS-DNS hybridization ruled out, that the strain belonged to any of the known Herbaspirillum species. Thus, the isolate, which might represent a new species, was named Herbaspirillum sp. N3. A specific, 16S rRNA targeted probe was constructed, which facilitated the examination of wheat roots colonization by this bacteria using FISH. Additionally the strain was GFP tagged to enable the detection in uncut root material. By this, an unequivocal demonstration of the endophytic colonization by Herbaspirillum sp. N3 mainly within the intercellular spaces was possible.In der vorliegenden Arbeit wurde die endophytische Besiedlung von Weizenwurzeln durch Azospirillum brasilense und Herbaspirillum sp. N3 untersucht. Mittels FISH-Methode mit artspezifischen phylogenetischen Oligonukleotidsonden und GFP-Markierungen konnte bei den A. brasilense Stämmen Sp7 und Sp245 an drei verschiedenen Weizensorten (Triticum aestivum) ein unterschiedliches Besiedlungsverhalten gezeigt werden. Hierzu wurde ein konfokales Laser-Scanning-Mikroskop verwendet, mit dem eine dreidimensionale Aufklärung der bakteriellen Besiedlung der Wurzel möglich war. Für diese Anwendung eigneten sich besonders die GFP-markierten Stämme, da die Detektion in diesem Falle ohne Vorbehandlung oder Schneiden der Wurzel erfolgen konnte. Stamm Sp7 konnte bei allen Kultivaren nur an der Oberfläche lokalisiert werden, während Stamm Sp245 auch inter- und intrazellulär in den äußeren Kortexschichten der Wurzel gefunden wurde. Es war kein Zusammenhang zwischen der wachstumsstimulierenden Wirkung des Inokulums (PGPR-Effekt) und der Lokalisierung der Bakterien nachweisbar. Der stärkste PGPR-Effekt konnte bei dem verwendeten brasilianischen Weizenkultivar dokumentiert werden, das offensichtlich aufgrund einer gewissen Anpassung an das Inokulum den größten Nutzen aus der bakteriellen Besiedlung zu ziehen vermochte. Da für den PGPR-Effekt die Produktion des Auxins IES (Indol-3-Essigsäure) von zentraler Bedeutung ist, wurde die Expression des Schlüsselgens ipdC (Indol-3-pyruvat Decarboxylase) einer genauen Untersuchung unterzogen. Dazu wurden eine Reihe von Methoden getestet, um eine Fusion des ipdC-Promotors mit einem gfp- oder rfp-Reportergen zu erzeugen. Durch die Konstruktion translationaler Promotorfusionen mit der gfp-Variante mut3 auf Plasmidebene waren Expressionsanalysen möglich. Dabei ergab sich, dass sich die unmittelbar strangaufwärts des ipdC-Startcodons gelegene Promotorregionen des Stammes Sp7 nur in wenigen Basen von der des Stammes Sp245 unterscheidet. Allerdings schließt sich strangaufwärts an diesen Bereich bei Stamm Sp245 ein etwa 150 Basenpaare messender Abschnitt an, der bei Stamm Sp7 fehlt. Durch die Konstruktion von zwei verschiedenen Fusionen, die einmal den zu Stamm Sp7 homologen Bereich und einmal die gesamte Promotorregion von Sp245 beinhalteten, konnte eine maßgebliche Bedeutung dieser nur bei Stamm Sp245 vorhandenen Region für Kontrolle und Stärke der ipdC-Expression in A. brasilense Sp245 nachgewiesen werden. Außerdem erfolgte durch die Zugabe von Phenylalanin und Tyrosin eine Induzierung der entsprechenden ipdC-Promotorfusionen bei Sp7 und Sp245. Dabei lag die maximale Promotoraktivität bei Stamm Sp7 höher als bei Stamm Sp245. Bei letzterem unterliegt die ipdC-Expression jedoch einer strengeren Kontrolle. Diese Ergebnisse wurden beim Einsatz der Transkonjuganden als Reporterstämme der ipdC-Expression auf Weizenwurzeln bestätigt. Es konnte eine Induzierbarkeit des ipdC-Promotors durch die Wurzelexsudate in situ nachgewiesen werden. Schließlich wurde das von oberflächensterilisierten Weizenwurzeln gewonnene Isolat N3 einer genaueren Charakterisierung unterzogen. Anhand der 16S rDNS Sequenzdaten ließ sich das Isolat phylogenetisch der Gattung Herbaspirillum zuordnen, wobei eine nachfolgende DNS-DNS-Hybridisierung die Zugehörigkeit zu einer der bekannten Herbaspirillum Spezies ausschloss. Für das demnach als Herbaspirillum sp. N3 bezeichnete Isolat, das möglicherweise den Vertreter einer neuen Art darstellt, wurde eine spezifische, 16S rRNS gerichtete Sonde entwickelt, mit der die Besiedlung von inokulierten Weizensorten durch diesen Bakterienstamm mittels FISH untersucht werden konnte. Außerdem wurde eine GFP-Markierung zur Detektion in ungeschnittenem Wurzelmaterial vorgenommen. Dabei ließ sich eindeutig eine endophytische Besiedlungsweise von Herbaspirillum sp. N3 demonstrieren, wobei das Bakterium bevorzugt in Interzellularräumen der Wurzel lokalisiert war

Endophytic root colonization of gramineous plants by Herbaspirillum frisingense

Herbaspirillum frisingense is a diazotrophic betaproteobacterium isolated from C4-energy plants, for example Miscanthus sinensis. To demonstrate endophytic colonization unequivocally, immunological labeling techniques using monospecific polyclonal antibodies against two H. frisingense strains and green fluorescent protein (GFP)-fluorescence tagging were applied. The polyclonal antibodies enabled specific in situ identification and very detailed localization of H. frisingense isolates Mb11 and GSF30T within roots of Miscanthus×giganteus seedlings. Three days after inoculation, cells were found inside root cortex cells and after 7 days they were colonizing the vascular tissue in the central cylinder. GFP-tagged H. frisingense strains could be detected and localized in uncut root material by confocal laser scanning microscopy and were found as endophytes in cortex cells, intercellular spaces and the central cylinder of barley roots. Concerning the production of potential plant effector molecules, H. frisingense strain GSF30T tested positive for the production of indole-3-acetic acid, while Mb11 was shown to produce N-acylhomoserine lactones, and both strains were able to utilize 1-aminocyclopropane-1-carboxylate (ACC), providing an indication of the activity of an ACC-deaminase. These results clearly present H. frisingense as a true plant endophyte and, although initial greenhouse experiments did not lead to clear plant growth stimulation, demonstrate the potential of this species for beneficial effects on the growth of crop plant

Monophyletic group of unclassified γ-Proteobacteria dominates in mixed culture biofilm of high-performing oxygen reducing biocathode

International audienceSeveral mixed microbial communities have been reported to show robust bioelectrocatalysis of oxygen reduction over time at applicable operation conditions. However, clarification of electron transfer mechanism(s) and identification of essential micro-organisms have not been realised. Therefore, the objective of this study was to shape oxygen reducing biocathodes with different microbial communities by means of surface modification using the electrochemical reduction of two different diazonium salts in order to discuss the relation of microbial composition and performance. The resulting oxygen reducing mixed culture biocathodes had complex bacterial biofilms variable in size and shape as observed by confocal and electron microscopy. Sequence analysis of ribosomal 16S rDNA revealed a putative correlation between the abundance of certain microbiota and biocathode performance. The best performing biocathode developed on the unmodified graphite electrode and reached a high current density for oxygen reducing biocathodes at neutral pH (0.9A/m(2)). This correlated with the highest domination (60.7%) of a monophyletic group of unclassified γ-Proteobacteria. These results corroborate earlier reports by other groups, however, higher current densities and higher presence of these unclassified bacteria were observed in this work. Therefore, members of this group are likely key-players for highly performing oxygen reducing biocathodes.[on SciFinder (R)

Diffusion and retention are major determinants of protein targeting to the inner nuclear membrane

Newly synthesized membrane proteins are constantly sorted from the endoplasmic reticulum (ER) to various membranous compartments. How proteins specifically enrich at the inner nuclear membrane (INM) is not well understood. We have established a visual in vitro assay to measure kinetics and investigate requirements of protein targeting to the INM. Using human LBR, SUN2, and LAP2 beta as model substrates, we show that INM targeting is energy-dependent but distinct from import of soluble cargo. Accumulation of proteins at the INM relies on both a highly interconnected ER network, which is affected by energy depletion, and an efficient immobilization step at the INM. Nucleoporin depletions suggest that translocation through nuclear pore complexes (NPCs) is rate-limiting and restricted by the central NPC scaffold. Our experimental data combined with mathematical modeling support a diffusion-retention-based mechanism of INM targeting. We experimentally confirmed the sufficiency of diffusion and retention using an artificial reporter lacking natural sorting signals that recapitulates the energy dependence of the process in vivo

Genome-based reclassification of azospirillum brasilense SP245 as the type strain of azospirillum baldaniorum sp. nov

Azospirillum sp. strain Sp245T, originally identified as belonging to Azospirillum brasilense, is recognized as a plant-growth-promoting rhizobacterium due to its ability to fix atmospheric nitrogen and to produce plant-beneficial compounds. Azospirillum sp. Sp245T and other related strains were isolated from the root surfaces of different plants in Brazil. Cells are Gram-negative, curved or slightly curved rods, and motile with polar and lateral flagella. Their growth temperature varies between 20 to 38 °C and their carbon source utilization is similar to other Azospirillum species. A preliminary 16S rRNA sequence analysis showed that the new species is closely related to A. brasilense Sp7T and A. formosense CC-Nfb-7T. Housekeeping genes revealed that Azospirillum sp. Sp245T, BR 12001 and Vi22 form a separate cluster from strain A. formosense CC-Nfb-7T, and a group of strains closely related to A. brasilense Sp7T. Overall genome relatedness index (OGRI) analyses estimated based on average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) between Azospirillum sp. Sp245T and its close relatives to other Azospirillum species type strains, such as A. brasilense Sp7T and A. formosense CC-Nfb-7T, revealed values lower than the limit of species circumscription. Moreover, core-proteome phylogeny including 1079 common shared proteins showed the independent clusterization of A. brasilense Sp7T, A. formosense CC-Nfb-7T and Azospirillum sp. Sp245T, a finding that was corroborated by the genome clustering of OGRI values and housekeeping phylogenies. The DNA G+C content of the cluster of Sp245T was 68.4–68.6%. Based on the phylogenetic, genomic, phenotypical and physiological analysis, we propose that strain Sp245T together with the strains Vi22 and BR12001 represent a novel species of the genus Azospirillum, for which the name Azospirillum baldaniorum sp. nov. is proposed. The type strain is Sp245T (=BR 11005T=IBPPM 219T) (GCF_007827915.1, GCF_000237365.1, and GCF_003119195.2).Fil: Ferreira, Natalia Dos Santos. Universidade Federal Rural Do Rio de Janeiro; BrasilFil: Sant´Anna, Fernando Hayashi. Universidade Federal do Rio Grande do Sul; BrasilFil: Reis, Veronica Massena. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil. Empresa Brasileira de Pesquisa Agropecuaria; BrasilFil: Ambrosini, Adriana. Universidade Federal do Rio Grande do Sul; BrasilFil: Volpiano, Camila Gazolla. Universidade Federal do Rio Grande do Sul; BrasilFil: Rothballer, Michael. Helmholtz Center Munich German Research Center For Environmental Health; AlemaniaFil: Schwab, Stefan. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil. Empresa Brasileira de Pesquisa Agropecuaria; BrasilFil: Baura, Valter Antonio. Universidade Federal do Paraná; BrasilFil: Balsanelli, Eduardo. Universidade Federal do Paraná; BrasilFil: Pedrosa, Fabio de Oliveira. Universidade Federal do Paraná; BrasilFil: Passaglia, Luciane Maria Pereira. Universidade Federal do Rio Grande do Sul; BrasilFil: de Souza, Emanuel Maltempi. Universidade Federal do Paraná; BrasilFil: Hartmann, Anton. Ludwig Maximilians Universitat; AlemaniaFil: Cassan, Fabricio Dario. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones Agrobiotecnológicas - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Agrobiotecnológicas; ArgentinaFil: Zilli, Jerri Edson. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil. Empresa Brasileira de Pesquisa Agropecuaria; Brasi

Impact of long-term agricultural management practices on therhizosphere microbiome and plant health

Increasing food and energy demands have resulted in a considerable intensification of farming practices, whichbrought about severe consequences for agricultural soils during last decades. In order to maintain soil quality andhealth for the future, the development of more extensive and sustainable farming strategies is urgently needed.The soil and rhizosphere microbiome play an integral role in virtually all soil processes and are intimately linkedto plant performance. Various studies indicated that agricultural management practices affect soil microbiomes.We therefore hypothesized that this external impact is conveyed by the microbial communities to the currentcrops at the time of their establishment. We used twelve differently managed soils from three long-term fieldtrials established in 1978 (Therwil, Switzerland), 1992 (Bernburg, Germany), and 2006 (Thyrow, Germany) toanalyze the impact of various management strategies (crop rotation, fertilization, tillage) on soil and its associatedrhizosphere microbiomes under consideration of plant productivity, plant health, and the ability of the soils tosuppress soil-borne phytopathogens. The model plant lettuce (Lactuca sativa L.) was cultivated for ten weeks undergrowth-chamber conditions in these soils. High-throughput sequencing of bacterial 16S rRNA genes or fungalITS fragments, respectively, PCR- amplified from total community DNA of rhizosphere and soil samples showedsignificant differences in microbial community compositions between soils that originated from the different fieldsites and long-term farming practices. Moreover, differences depending on long-term agricultural managementin plant productivity and health as measured by RT-qPCR of stress-related plant genes were observed. Localizedanalysis of rhizosphere soil solution was performed using non-invasive sampling techniques with sorption filtersplaced onto the surface of soil-grown roots along the root observation windows with subsequent HPLC-MSprofiling. Amino acids, sugars and antifungal organic acids such as benzoic acid detected in the rhizosphere soilsolutions confirmed variations in concentrations depending on the site and management practice indicating differ-ent stress potentials of farming practices for plants. Agricultural management also affected soil suppressiveness tothe soil-borne model pathogen Rhizoctonia solani.Under controlled growth chamber conditions, we could show the legacy of long-term agricultural managementpractices on the establishment and performance of a subsequent plant generation and its associated rhizospheremicrobiome

Microbial community structure elucidates performance of Glyceria maxima plant microbial fuel cell

The plant microbial fuel cell (PMFC) is a technology in which living plant roots provide electron donor, via rhizodeposition, to a mixed microbial community to generate electricity in a microbial fuel cell. Analysis and localisation of the microbial community is necessary for gaining insight into the competition for electron donor in a PMFC. This paper characterises the anode–rhizosphere bacterial community of a Glyceria maxima (reed mannagrass) PMFC. Electrochemically active bacteria (EAB) were located on the root surfaces, but they were more abundant colonising the graphite granular electrode. Anaerobic cellulolytic bacteria dominated the area where most of the EAB were found, indicating that the current was probably generated via the hydrolysis of cellulose. Due to the presence of oxygen and nitrate, short-chain fatty acid-utilising denitrifiers were the major competitors for the electron donor. Acetate-utilising methanogens played a minor role in the competition for electron donor, probably due to the availability of graphite granules as electron acceptors