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153 Publications visible to you, out of a total of 153
Facile carbohydrate-mimetic modifications of poly(ethylene imine) carriers for gene delivery applications

Abstract (Expand)

Commercially-available linear and branched PEIs (LPEI and BPEI) were chemically-modified with carbohydrates and carbohydrate-mimetics to improve biocompatibility. Hydroxyl moieties were installed in a … close proximity via reaction of PEI's amines with paraformaldehyde (pF) or glycidol. Mixing PEI with pF led to the formation of hemiaminal moieties as well as N-methylation of the backbone through an Eschweiler–Clarke-type rearrangement. The amount of attached hydroxyl groups depended on the initial amount of pF and the results were in agreement with NMR studies on model reactions with primary and secondary amines. The primary amines of BPEI triggered the ring-opening of glycidol and sugar-containing epoxides, in methanol and at room temperature. PEI chains modified with pF displayed the same cytotoxicity as the parent polymer, unless a sufficient amount of pF was added to trigger N-methylation of the backbone. In contrast, glycidol and sugar-functionalized BPEIs exhibited lower toxicity but similar (if not higher) transfection efficiency as compared to unmodified BPEI.

Authors: Christoph Englert, Mareva Fevre, Rudy J. Wojtecki, Wei Cheng, Qingxing Xu, Chuan Yang, Xiyu Ke, Matthias Hartlieb, Kristian Kempe, Jeannette M. García, Robert J. Ono, Ulrich S. Schubert, Yi Yan Yang, James L. Hedrick

Date Published: No date defined

Publication Type: Not specified

Ferrihydrite associated organic matter (OM) stimulates reduction by <i>Shewanella oneidensis</i> MR-1 and a complex microbial consortia

Abstract (Expand)

The formation of Fe(III) oxides in natural environments occurs in the presence of natural organic matter (OM), resulting in the formation of OM-mineral complexes that form through adsorption or … coprecipitation processes. Thus, microbial Fe(III) reduction in natural environments most often occurs in the presence of OM-mineral complexes rather than pure Fe(III) minerals. In this study we investigated to which extent the content of adsorbed or coprecipitated OM on ferrihydrite influences the rate of Fe(III) reduction by Shewanella oneidensis MR-1, a model Fe(III)-reducing microorganism, in comparison to a microbial consortium extracted from the acidic, Fe-rich Schlöppnerbrunnen fen. We found that increased OM contents led to increased rates of microbial Fe(III) reduction by S. oneidensis MR-1 in contrast to earlier findings with the model organism Geobacter bremensis. Ferrihydrite-OM coprecipitates were reduced slightly faster than ferrihydrites with adsorbed OM. Surprisingly, the complex microbial consortia stimulated by a mixture of electrons donors (lactate, acetate, and glucose) mimics S. oneidensis under the same experimental Fe(III)-reducing conditions suggesting similar mechanisms of electron transfer whether or not the OM is adsorbed or coprecipitated to the mineral surfaces. We also followed potential shifts of the microbial community during the incubation via 16S rRNA gene sequence analyses to determine variations due to the presence of adsorbed or coprecipitated OM-ferrihydrite complexes in contrast to pure ferrihydrite. Community profile analyses showed no enrichment of typical model Fe(III)-reducing bacteria, such as Shewanella sp. or Geobacter sp., but an enrichment of fermenters (i.e. Enterobacteria) during pure ferrihydrite incubations which are known to use Fe(III) as an electron sink. Instead, OM-mineral complexes favored the enrichment of microbes including Desulfobacteria and Pelosinus sp., both of which can utilize lactate and acetate as an electron donor under Fe(III) reducing conditions. In summary, this study shows that increasing concentrations of OM in OM-mineral complexes determines microbial Fe(III) reduction rates and shapes the microbial community structure involved in the reductive dissolution of ferrihydrite. Similarities observed between the complex Fe(III)-reducing microbial consortia and the model Fe(III)-reducer S. oneidensis MR-1 suggest electron shuttling mechanisms dominate in OM-rich environments, including soils, sediments, and fens, where natural OM interacts with Fe(III) oxides during mineral formation.

Authors: Rebecca E. Cooper, Karin Eusterhues, Carl-Eric Wegner, Kai Uwe Totsche, Kirsten Küsel

Date Published: 6th Jul 2017

Publication Type: Not specified

Food-Poisoning Bacteria Employ a Citrate Synthase and a Type II NRPS To Synthesize Bolaamphiphilic Lipopeptide Antibiotics.

Abstract (Expand)

Mining the genome of the food-spoiling bacterium Burkholderia gladioli pv. cocovenenans revealed five nonribosomal peptide synthetase (NRPS) gene clusters, including an orphan gene locus (bol). Gene … inactivation and metabolic profiling linked the bol gene cluster to novel bolaamphiphilic lipopeptides with antimycobacterial activity. A combination of chemical analysis and bioinformatics elucidated the structures of bolagladin A and B, lipocyclopeptides featuring an unusual dehydro-beta-alanine enamide linker fused to an unprecedented tricarboxylic fatty acid tail. Through a series of targeted gene deletions, we proved the involvement of a designated citrate synthase (CS), priming ketosynthases III (KS III), a type II NRPS, including a novel desaturase for enamide formation, and a multimodular NRPS in generating the cyclopeptide. Network analyses revealed the evolutionary origin of the CS and identified cryptic CS/NRPS gene loci in various bacterial genomes.

Authors: B. Dose, C. Ross, S. P. Niehs, K. Scherlach, J. P. Bauer, C. Hertweck

Date Published: 11th Aug 2020

Publication Type: Not specified

Frankobactin Metallophores Produced by Nitrogen-Fixing Frankia Actinobacteria Function in Toxic Metal Sequestration.

Abstract (Expand)

A series of new metallophores, referred to as frankobactins, were extracted from cultures of the symbiotic and nitrogen-fixing actinobacterium Frankia sp. CH37. Structure elucidation revealed a … 2-hydroxyphenyl-substituted oxazoline core and a chain composed of five proteinogenic and nonproteinogenic amino acids, suggesting nonribosomal peptide synthesis as the biosynthetic origin. By whole-genome sequencing, bioinformatic analysis, and comparison with other Frankia strains, the genetic locus responsible for the biosynthesis was detected. Spectrophotometric titration of frankobactin with Fe(III) and Cu(II) and mass spectrometry established the 1:1 (metal:frankobactin) coordination. Uptake experiments suggested that frankobactin A1 (1) did not serve to recruit iron, but to detoxify Cu(II). As frankobactin A1 prevents the cellular entry of Cu(II), it could play a crucial role in the symbiosis of Frankia sp. and its host in the reclamation of copper-contaminated soil.

Authors: J. F. Mohr, F. Baldeweg, M. Deicke, C. F. Morales-Reyes, D. Hoffmeister, T. Wichard

Date Published: 23rd Apr 2021

Publication Type: Journal

Functional genomic profiling of Aspergillus fumigatus biofilm reveals enhanced production of the mycotoxin gliotoxin

Abstract (Expand)

The opportunistic pathogenic mold Aspergillus fumigatus is an increasing cause of morbidity and mortality in immunocompromised and in part immunocompetent patients. A. fumigatus can grow in multicellular … communities by the formation of a hyphal network encased in an extracellular matrix. Here, we describe the proteome and transcriptome of planktonic- and biofilm-grown A. fumigatus mycelium after 24 and 48 h. A biofilm- and time-dependent regulation of many proteins and genes of the primary metabolism indicates a developmental stage of the young biofilm at 24 h, which demands energy. At a matured biofilm phase, metabolic activity seems to be reduced. However, genes, which code for hydrophobins, and proteins involved in the biosynthesis of secondary metabolites were significantly upregulated. In particular, proteins of the gliotoxin secondary metabolite gene cluster were induced in biofilm cultures. This was confirmed by real-time PCR and by detection of this immunologically active mycotoxin in culture supernatants using HPLC analysis. The enhanced production of gliotoxin by in vitro formed biofilms reported here may also play a significant role under in vivo conditions. It may confer A. fumigatus protection from the host immune system and also enable its survival and persistence in chronic lung infections such as aspergilloma.

Authors: S. Bruns, M. Seidler, D. Albrecht, S. Salvenmoser, N. Remme, C. Hertweck, A. A. Brakhage, O. Kniemeyer, F. M. Muller

Date Published: 21st Jul 2010

Publication Type: Not specified

Functional Variation in Dipteran Gut Bacterial Communities in Relation to Their Diet, Life Cycle Stage and Habitat.

Abstract (Expand)

True flies and mosquitos (Diptera) live in habitats and consume diets that pose specific demands on their gut bacterial communities (GBCs). Due to diet specializations, dipterans may have highly diverse … and species-specific GBCs. Dipterans are also confronted with changes in habitat and food sources over their lifetime, especially during life history processes (molting, metamorphosis). This may prevent the development of a constant species- or diet-specific GBC. Some dipterans are vectors of several human pathogens (e.g., malaria), which interact with GBCs. In this review, we explore the dynamics that shape GBC composition in some Diptera species on the basis of published datasets of GBCs. We thereby focus on the effects of diet, habitats, and life cycle stages as sources of variation in GBC composition. The GBCs reported were more stage-specific than species- or diet-specific. Even though the presence of GBCs has a large impact on the performance of their hosts, the exact functions of GBCs and their interactions with other organisms are still largely unknown, mainly due to the low number of studies to date. Increasing our knowledge on dipteran GBCs will help to design pest management strategies for the reduction of insecticide resistance, as well as for human pathogen control.

Authors: R. Sontowski, N. M. van Dam

Date Published: 17th Aug 2020

Publication Type: Journal

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