Total Synthesis of Pyoverdin D

Pyoverdin D is an important siderophore that is used by the human pathogen <i>Pseudomonas aeruginosa</i> to import iron and gain a competitive advantage. This unique partially cyclic octapeptide bears four nonproteinogenic amino acids, including ^δ<i>N</i>-formyl-^δ<i>N</i>-hydroxy-l-ornithine, and a catechol containing chiral chromophore. Here, we report the first total synthesis of pyoverdin D

<i>Vibrio cholerae</i> Autoinducer CAI-1 Interferes with <i>Pseudomonas aeruginosa</i> Quorum Sensing and Inhibits its Growth

The human pathogen <i>Vibrio cholerae</i> uses several small molecules to coordinate gene expression in a process termed quorum sensing (QS), and its main autoinducer is CAI-1. We have examined the activity of this signaling molecule in three other species of bacteria. Interestingly, while showing an inhibitory effect on QS in the opportunistic pathogen <i>P. aeruginosa</i> at low micromolar concentrations, it caused also growth inhibition at higher concentrations. In contrast, the two other bacteria were unaffected, and we suggest a possible mechanism for these effects, based on membrane perturbation studies

Mining Plants for Bacterial Quorum Sensing Modulators

The bacterial plant pathogen <i>Agrobacterium tumefaciens</i> uses quorum sensing (QS) in order to regulate the transfer of DNA into the host plant genome, and this results in the induction of crown gall tumors. The deleterious results of these infections are widespread and affect many species of fruit and crops. In order to further our understanding of this process and to provide potential solutions, we evaluated a library of 3800 natural products from plant sources and identified potent compounds that are able to strongly modulate plant–bacterial interactions

Effects of 3OC₁₂HSL on <i>P. aeruginosa</i>, <i>S. aureus</i>, and <i>C. albicans</i> that are relevant to immune recognition.

<p>Lines ending in arrows indicate induction and lines ending in circles indicate inhibition of the indicated process. <i>C. albicans</i>, in the hyphal morphology, induces phagotycosis during inflammation (1). Virulent hyphae can be inhibited and transformed to yeast cells by farnesol, the QS molecule secreted by <i>C. albicans</i> (2). <i>Candida</i> yeast cells prevent macrophages induction (3) and render <i>C. albicans</i> invisible for the immune system. <i>C. albicans</i> coexisting with <i>P. aeruginosa</i> exerts a double-sided reaction; farnesol inhibits <i>Pseudomonas</i> QS production (4), whereas 3OC₁₂HSL secreted by <i>P. aeruginosa</i> prevents <i>C. albicans</i> filamentation without changing the growth rate (5). 3OC₁₂HSL sensed by the host induces a pro-inflammatory response by activation of macrophages (6), but it can also give an anti-inflammatory reaction by selectively diminishing the regulation of NF-κB signaling and attenuating TLR4-dependent innate immune responses (7). <i>P. aeruginosa</i> 3OC₁₂HSL influences <i>S. aureus</i> by inhibiting growth and hemolysin and exotoxin production (8) and by inducing protein A expression (9), which prevents recognition of <i>S. aureus</i> by macrophages and neutrophils (10). <i>S. aureus</i> detected by the immune system trigger macrophages signaling pathways (11).</p

Schematic overview of the complex QS systems present in <i>P. aeruginosa</i>.

<p>The commanders represent the major regulatory systems, while the messengers are the signaling molecules. The soldiers represent the various virulence factors that have a function in the interaction of <i>P. aeruginosa</i> with the host.</p

Data_Sheet_1_The reduction of environmentally abundant iron oxides by the methanogen Methanosarcina barkeri.docx

Microbial dissimilatory iron reduction is a fundamental respiratory process that began early in evolution and is performed in diverse habitats including aquatic anoxic sediments. In many of these sediments microbial iron reduction is not only observed in its classical upper zone, but also in the methane production zone, where low-reactive iron oxide minerals are present. Previous studies in aquatic sediments have shown the potential role of the archaeal methanogen Methanosarcinales in this reduction process, and their use of methanophenazines was suggested as an advantage in reducing iron over other iron-reducing bacteria. Here we tested the capability of the methanogenic archaeon Methanosarcina barkeri to reduce three naturally abundant iron oxides in the methanogenic zone: the low-reactive iron minerals hematite and magnetite, and the high-reactive amorphous iron oxide. We also examined the potential role of their methanophenazines in promoting the reduction. Pure cultures were grown close to natural conditions existing in the methanogenic zone (under nitrogen atmosphere, N2:CO2, 80:20), in the presence of these iron oxides and different electron shuttles. Iron reduction by M. barkeri was observed in all iron oxide types within 10 days. The reduction during that time was most notable for amorphous iron, then magnetite, and finally hematite. Importantly, the reduction of iron inhibited archaeal methane production. When hematite was added inside cryogenic vials, thereby preventing direct contact with M. barkeri, no iron reduction was observed, and methanogenesis was not inhibited. This suggests a potential role of methanophenazines, which are strongly associated with the membrane, in transferring electrons from the cell to the minerals. Indeed, adding dissolved phenazines as electron shuttles to the media with iron oxides increased iron reduction and inhibited methanogenesis almost completely. When M. barkeri was incubated with hematite and the phenazines together, there was a change in the amounts (but not the type) of specific metabolites, indicating a difference in the ratio of metabolic pathways. Taken together, the results show the potential role of methanogens in reducing naturally abundant iron minerals in methanogenic sediments under natural energy and substrate limitations and shed new insights into the coupling of microbial iron reduction and the important greenhouse gas methane.</p

Dataset for: The regulatory significance of tag recycling in the mycobacterial Pup-proteasome system

Pup, a ubiquitin analog, tags proteins for degradation by the bacterial proteasome. As an intracellular proteolytic system, the Pup-proteasome system (PPS) must be carefully regulated to prevent excessive protein degradation. Currently, those factors underlying PPS regulation remain poorly understood. Here, experimental analysis combined with theoretical modeling of in vivo protein pupylation revealed how the basic PPS design allows stable and controlled protein pupylation. Specifically, the recycling of Pup when targets are degraded allows the PPS to maintain steady state levels of protein pupylation and degradation at a rate limited by proteasome function, and at a pupylome level limited by Pup concentrations. This design allows the Pup-ligase, a highly promiscuous enzyme, to act in a controlled manner without causing damage, and the PPS to be effectively tuned to control protein degradation. This study thus provides understanding of how the inherent design of an intracellular proteolytic system serves crucial regulatory purposes

Surface Display of a Redox Enzyme and its Site-Specific Wiring to Gold Electrodes

The generation of a current through interaction between bacteria and electrodes has been explored by various methods. We demonstrate the attachment of living bacteria through a surface displayed redox enzyme, alcohol dehydrogenase II. The unnatural amino acid para-azido-l-phenylalanine was incorporated into a specific site of the displayed enzyme, facilitating electron transfer between the enzyme and an electrode. In order to attach the bacteria carrying the surface displayed enzyme to a surface, a linker containing an alkyne and a thiol moiety on opposite ends was synthesized and attached to the dehydrogenase site specifically through a copper­(I)-catalyzed azide–alkyne cycloaddition reaction. Using this approach we were able to covalently link bacteria to gold-coated surfaces and to gold nanoparticles, while maintaining viability and catalytic activity. We show the performance of a biofuel cell using these modified bacteria at the anode, which resulted in site-specific dependent fuel cell performance for at least a week. This is the first example of site-specific attachment of a true living biohybrid to inorganic material