microLife最新文献

About the scientific life of Melanie Blokesch.

About the scientific life of Judith Behnsen.

The recent discovery that giant viruses encode proteins related to sugar synthesis and processing paved the way for the study of their glycosylation machinery. We focused on the proposed Megavirinae subfamily, for which glycan-related genes were proposed to code for proteins involved in glycosylation of the layer of fibrils surrounding their icosahedral capsids. We compared sugar compositions and corresponding biosynthetic pathways among clade members using a combination of chemical and bioinformatics approaches. We first demonstrated that Megavirinae glycosylation differs in many aspects from what was previously reported for viruses, as they have complex glycosylation gene clusters made of six and up to 33 genes to synthetize their fibril glycans (biosynthetic pathways for nucleotide-sugars and glycosyltransferases). Second, they synthesize rare amino-sugars, usually restricted to bacteria and absent from their eukaryotic host. Finally, we showed that Megavirinae glycosylation is clade-specific and that Moumouvirus australiensis, a B-clade outsider, shares key features with Cotonvirus japonicus (clade E) and Tupanviruses (clade D). The existence of a glycosylation toolbox in this family could represent an advantageous strategy to survive in an environment where members of the same family are competing for the same amoeba host. This study expands the field of viral glycobiology and raises questions on how Megavirinae evolved such versatile glycosylation machinery.

Bacterial membrane vesicles (MVs) have been reported to kill other bacteria. In the case of Pseudomonas aeruginosa the bactericidal activity has been attributed to an unidentified 26 kDa peptidoglycan (PG) hydrolase that is associated with MVs and gives rise to a lytic band on zymograms using murein sacculi as substrate. In this study, we employed a proteomics approach to show that this PG hydrolase is the AmphD3 amidase. The analysis of an amphD3 mutant as well as of an AmphD3 overexpression derivative revealed that this enzyme is not required for the bactericidal activity of P. aeruginosa MVs but is involved in cell wall recycling and thus protects the cell against PG damage. Another 23 kDa PG hydrolase, which we observed on zymograms of SOS-induced MVs, was identified as the endolysin Lys, which triggers explosive cell lysis but is shown to be dispensable for MV-mediated killing. We conclude that the lytic activities observed on zymograms do not correlate with the bactericidal potential of MVs. We demonstrate that P. aeruginosa MVs are enriched for several autolysins, suggesting that the predatory activity of MVs depends on the combined action of different murein hydrolases.

Iron is involved in numerous biological processes in both prokaryotes and eukaryotes and is therefore subject to a tug-of-war between host and microbes upon pathogenic infections. In the fruit fly Drosophila melanogaster, the iron transporter Transferrin 1 (Tsf1) mediates iron relocation from the hemolymph to the fat body upon infection as part of the nutritional immune response. The sequestration of iron in the fat body renders it less available for pathogens, hence limiting their proliferation and enhancing the host ability to fight the infection. Here we investigate the interaction between host iron homeostasis and Spiroplasma poulsonii, a facultative, vertically transmitted, endosymbiont of Drosophila. This low-pathogenicity bacterium is devoid of cell wall and is able to thrive in the host hemolymph without triggering pathogen-responsive canonical immune pathways. However, hemolymph proteomics revealed an enrichment of Tsf1 in infected flies. We find that S. poulsonii induces tsf1 expression and triggers an iron sequestration response similarly to pathogenic bacteria. We next demonstrate that free iron cannot be used by Spiroplasma while Tsf1-bound iron promotes bacterial growth, underlining the adaptation of Spiroplasma to the intra-host lifestyle where iron is mostly protein-bound. Our results show that Tsf1 is used both by the fly to sequester iron and by Spiroplasma to forage host iron, making it a central protein in endosymbiotic homeostasis.

Budding of the bacterial surface results in the formation and secretion of outer membrane vesicles, which is a conserved phenomenon observed in Gram-negative bacteria. Recent studies highlight that these sphere-shaped facsimiles of the donor bacterium's surface with enclosed periplasmic content may serve multiple purposes for their host bacterium. These include inter- and intraspecies cell-cell communication, effector delivery to target cells and bacterial adaptation strategies. This review provides a concise overview of potential medical applications to exploit outer membrane vesicles for therapeutic approaches. Due to the fact that outer membrane vesicles resemble the surface of their donor cells, they represent interesting nonliving candidates for vaccine development. Furthermore, bacterial donor species can be genetically engineered to display various proteins and glycans of interest on the outer membrane vesicle surface or in their lumen. Outer membrane vesicles also possess valuable bioreactor features as they have the natural capacity to protect, stabilize and enhance the activity of luminal enzymes. Along these features, outer membrane vesicles not only might be suitable for biotechnological applications but may also enable cell-specific delivery of designed therapeutics as they are efficiently internalized by nonprofessional phagocytes. Finally, outer membrane vesicles are potent modulators of our immune system with pro- and anti-inflammatory properties. A deeper understanding of immunoregulatory effects provoked by different outer membrane vesicles is the basis for their possible future applications ranging from inflammation and immune response modulation to anticancer therapy.

In recent years, the interplay of epigenetics and infection moved into the limelight. Epigenetic regulation describes modifications in gene expression without alterations of the DNA sequence. In eukaryotes, this mechanism is central for fundamental cellular processes such as cell development and differentiation, but it is also involved in more specific tasks such as the response to infection by a pathogen. One of the most common types of epigenetic changes is the modification of histones. Histones, the small protein building blocks that are wrapped with DNA are the fundamental packaging unit of chromatin. Histones can be modified by linking different moieties to them-one of the most abundant ones is acetylation. Histone acetylation is regulated by two main classes of enzymes, histone acetyl transferases (HAT) and their counterparts, histone deacetylases (HDAC). Given the high abundance and importance in regulating gene expression, histone acetylation is an excellent target for pathogens to manipulate the host cell to their advantage. Targeting HDACs gained particular interest in recent years, due to the increased use of HDAC inhibitors in clinical practice. Recently, the possibility to fight an infection with HDAC inhibitors was suggested as an alternative to overcome the ever-growing problem of antibiotic resistance. In this review, we focus on the regulation of HDACs and their involvement in immune cell function. We then highlight different mechanisms employed by pathogens to manipulate histone deacetylases and we discuss the possibility of HDAC inhibitors as therapeutics to fight infections.

Extracellular vesicles (EVs) are lipidic nanosized particles that deliver a highly complex molecular cargo between cells and organisms and may serve numerous functions in intercellular communication, thereby influencing the evolution of microbial communities. Their roles in infectious diseases have been studied for a long time, comprising viral, bacterial, parasitic and to a less extent, fungal infections. Over the last few years, fungal EVs have become an increasingly active research field. Nevertheless, the understanding of EV functions during fungal infections poses challenging points, comprising the genetics regulating EV release, the EV structural and compositional complexity, the heterogeneity of the EV populations and their impact on host-pathogen interactions. This review explores the state-of-the-art investigations on fungal EVs and how this fast-evolving field can impact the development of new tools to fight fungal infections.

Membrane-bound extracellular vesicles (EVs) are secreted by cells from all three domains of life and their implication in various biological processes is increasingly recognized. In this review, we summarize the current knowledge on archaeal EVs and nanotubes, and emphasize their biological significance. In archaea, the EVs and nanotubes have been largely studied in representative species from the phyla Crenarchaeota and Euryarchaeota. The archaeal EVs have been linked to several physiological processes such as detoxification, biomineralization and transport of biological molecules, including chromosomal, viral or plasmid DNA, thereby taking part in genome evolution and adaptation through horizontal gene transfer. The biological significance of archaeal nanotubes is yet to be demonstrated, although they could participate in EV biogenesis or exchange of cellular contents. We also discuss the biological mechanisms leading to EV/nanotube biogenesis in Archaea. It has been recently demonstrated that, similar to eukaryotes, EV budding in crenarchaea depends on the ESCRT machinery, whereas the mechanism of EV budding in euryarchaeal lineages, which lack the ESCRT-III homologues, remains unknown.

The gut microbiota plays an integral role in human health and its dysbiosis is associated with many chronic diseases. There are still large gaps in understanding the host and environmental factors that directly regulate the gut microbiota, and few effective strategies exist to modulate the microbiota in therapeutic applications. Recent reports suggest that certain microRNAs (miRNAs) released by mammalian cells can regulate bacterial gene expression to influence the microbiome composition and propose extracellular vesicles as one natural mechanism for miRNA transport in the gut. These new findings interface with a burgeoning body of data showing that miRNAs are present in a stable form in extracellular environments and can mediate cell-to-cell communication in mammals. Here, we review the literature on RNA-mediated modulation of the microbiome to bring cross-disciplinary perspective to this new type of interaction and its potential implications in biology and medicine.