Marcos Pires

Abstract

by Ziad Al Nabhani, Gilles Dietrich, Jean-Pierre Hugot, Frederick Barreau

Nucleotide-binding oligomerization domain 2 (NOD2) is an intracellular pattern recognition receptor that senses bacterial peptidoglycan (PGN)-conserved motifs in cytosol and stimulates host immune response. The association of NOD2 mutations with a number of inflammatory pathologies, including Crohn disease (CD), Graft-versus-host disease (GVHD), and Blau syndrome, highlights its pivotal role in host–pathogen interactions and inflammatory response. Stimulation of NOD2 by its ligand (muramyl dipeptide) activates pro-inflammatory pathways such as nuclear factor-κB (NF-κB), mitogen-activated protein kinases (MAPKs), and Caspase-1. A loss of NOD2 function may result in a failure in the control of microbial infection, thereby initiating systemic responses and aberrant inflammation. Because the ligand of Nod2 is conserved in both gram-positive and gram-negative bacteria, NOD2 detects a wide variety of microorganisms. Furthermore, current literature evidences that NOD2 is also able to control viruses’ and parasites’ infections. In this review, we present and discuss recent developments about the role of NOD2 in shaping the gut commensal microbiota and pathogens, including bacteria, viruses, and parasites, and the mechanisms by which Nod2 mutations participate in disease occurrence.

A 3D organ culture system preserves the intestine architecture and allows modeling the interactions between intestinal cells, the immune system, microbes, and nutrients.

Controlled experimental evolution during antibiotic treatment can help to explain the processes leading to antibiotic resistance in bacteria. Recently, intermittent antibiotic exposures have been shown to lead rapidly to the evolution of tolerance—that is, the ability to survive under treatment without developing resistance. However, whether tolerance delays or promotes the eventual emergence of resistance is unclear. Here we used in vitro evolution experiments to explore this question. We found that in all cases, tolerance preceded resistance. A mathematical population-genetics model showed how tolerance boosts the chances for resistance mutations to spread in the population. Thus, tolerance mutations pave the way for the rapid subsequent evolution of resistance. Preventing the evolution of tolerance may offer a new strategy for delaying the emergence of resistance. Authors: Irit Levin-Reisman, Irine Ronin, Orit Gefen, Ilan Braniss, Noam Shoresh, Nathalie Q. Balaban

Mechanisms of envelope permeability and antibiotic influx and efflux in Gram-negative bacteria

Nature Microbiology, Published online: 22 February 2017; doi:10.1038/nmicrobiol.2017.1

A Perspective on unravelling the mechanisms of antibiotic penetration and efflux in Gram-negative bacteria.

Bacterial physiology: Wrapping the cell in a CozE shell

Nature Microbiology, Published online: 22 February 2017; doi:10.1038/nmicrobiol.2016.262

Recent work characterizing CozE, a protein that controls the function of the class A penicillin-binding protein PBP1a, sheds new light on our understanding of the synthesis of the bacterial peptidoglycan shell.

The mechanism by which bacteria divide is not well understood. Cell division is mediated by filaments of FtsZ and FtsA (FtsAZ) that recruit septal peptidoglycan-synthesizing enzymes to the division site. To understand how these components coordinate to divide cells, we visualized their movements relative to the dynamics of cell wall synthesis during cytokinesis. We found that the division septum was built at discrete sites that moved around the division plane. FtsAZ filaments treadmilled circumferentially around the division ring and drove the motions of the peptidoglycan-synthesizing enzymes. The FtsZ treadmilling rate controlled both the rate of peptidoglycan synthesis and cell division. Thus, FtsZ treadmilling guides the progressive insertion of new cell wall by building increasingly smaller concentric rings of peptidoglycan to divide the cell. Authors: Alexandre W. Bisson-Filho, Yen-Pang Hsu, Georgia R. Squyres, Erkin Kuru, Fabai Wu, Calum Jukes, Yingjie Sun, Cees Dekker, Seamus Holden, Michael S. VanNieuwenhze, Yves V. Brun, Ethan C. Garner

Each of 53 human-resident bacterial species studied in monoculture in mice modulates the host immune system, providing a baseline for investigating how consortia of gut microbes interact with their host.

Abstract

Cysteine can be specifically functionalized by a myriad of acid-base conjugation strategies for applications ranging from probing protein function to antibody-drug conjugates and proteomics. In contrast, selective ligation to the other sulfur-containing amino acid, methionine, has been precluded by its intrinsically weaker nucleophilicity. Here, we report a strategy for chemoselective methionine bioconjugation through redox reactivity, using oxaziridine-based reagents to achieve highly selective, rapid, and robust methionine labeling under a range of biocompatible reaction conditions. We highlight the broad utility of this conjugation method to enable precise addition of payloads to proteins, synthesis of antibody-drug conjugates, and identification of hyperreactive methionine residues in whole proteomes.

Nature Chemical Biology 13, 268 (2017). doi:10.1038/nchembio.2268

Authors: Shu-Lin Liu, Ren Sheng, Jae Hun Jung, Li Wang, Ewa Stec, Matthew J O'Connor, Seohyoen Song, Rama Kamesh Bikkavilli, Robert A Winn, Daesung Lee, Kwanghee Baek, Kazumitsu Ueda, Irena Levitan, Kwang-Pyo Kim & Wonhwa Cho

Nature Chemical Biology 13, 265 (2017). doi:10.1038/nchembio.2270

Authors: Jonna K Hakulinen, Jenny Hering, Gisela Brändén, Hongming Chen, Arjan Snijder, Margareta Ek & Patrik Johansson

The rapid increase of antibiotic resistance has created an urgent need to develop novel antimicrobial agents. Here we describe the crystal structure of the promising bacterial target phospho-N-acetylmuramoyl–pentapeptide translocase (MraY) in complex with the nucleoside antibiotic tunicamycin. The structure not only reveals the mode of action of several related natural-product antibiotics but also gives an indication on the binding mode of the MraY UDP–MurNAc–pentapeptide and undecaprenyl-phosphate substrates.

Synergistic effects of vancomycin and β-lactams against vancomycin highly resistant Staphylococcus aureus

The Journal of Antibiotics advance online publication, February 15 2017. doi:10.1038/ja.2017.7

Authors: Fumiaki Tabuchi, Yasuhiko Matsumoto, Masaki Ishii, Keita Tatsuno, Mitsuhiro Okazaki, Tomoaki Sato, Kyoji Moriya & Kazuhisa Sekimizu

Dynamics of the human gut microbiome in inflammatory bowel disease

Nature Microbiology, Published online: 13 February 2017; doi:10.1038/nmicrobiol.2017.4

The long-term dynamic behaviour of the gut microbiome in inflammatory bowel disease demonstrates increased deviation from the ‘healthy plane’ when compared to the normal variation observed in healthy individuals.

Cysteine can be specifically functionalized by a myriad of acid-base conjugation strategies for applications ranging from probing protein function to antibody-drug conjugates and proteomics. In contrast, selective ligation to the other sulfur-containing amino acid, methionine, has been precluded by its intrinsically weaker nucleophilicity. Here, we report a strategy for chemoselective methionine bioconjugation through redox reactivity, using oxaziridine-based reagents to achieve highly selective, rapid, and robust methionine labeling under a range of biocompatible reaction conditions. We highlight the broad utility of this conjugation method to enable precise addition of payloads to proteins, synthesis of antibody-drug conjugates, and identification of hyperreactive methionine residues in whole proteomes. Authors: Shixian Lin, Xiaoyu Yang, Shang Jia, Amy M. Weeks, Michael Hornsby, Peter S. Lee, Rita V. Nichiporuk, Anthony T. Iavarone, James A. Wells, F. Dean Toste, Christopher J. Chang

The human microbiome encodes vast numbers of uncharacterized enzymes, limiting our functional understanding of this community and its effects on host health and disease. By incorporating information about enzymatic chemistry into quantitative metagenomics, we determined the abundance and distribution of individual members of the glycyl radical enzyme superfamily among the microbiomes of healthy humans. We identified many uncharacterized family members, including a universally distributed enzyme that enables commensal gut microbes and human pathogens to dehydrate trans-4-hydroxy-l-proline, the product of the most abundant human posttranslational modification. This “chemically guided functional profiling” workflow can therefore use ecological context to facilitate the discovery of enzymes in microbial communities. Authors: B. J. Levin, Y. Y. Huang, S. C. Peck, Y. Wei, A. Martínez-del Campo, J. A. Marks, E. A. Franzosa, C. Huttenhower, E. P. Balskus

ABSTRACT

Persisters are dormant variants that form a subpopulation of cells tolerant to antibiotics. Persisters are largely responsible for the recalcitrance of chronic infections to therapy. In Escherichia coli, one widely accepted model of persister formation holds that stochastic accumulation of ppGpp causes activation of the Lon protease that degrades antitoxins; active toxins then inhibit translation, resulting in dormant, drug-tolerant persisters. We found that various stresses induce toxin-antitoxin (TA) expression but that induction of TAs does not necessarily increase persisters. The 16S rRNA promoter rrnB P1 was proposed to be a persister reporter and an indicator of toxin activation regulated by ppGpp. Using fluorescence-activated cell sorting (FACS), we confirmed the enrichment for persisters in the fraction of rrnB P1-gfp dim cells; however, this is independent of toxin-antitoxins. rrnB P1 is coregulated by ppGpp and ATP. We show that rrnB P1 can report persisters in a relA/spoT deletion background, suggesting that rrnB P1 is a persister marker responding to ATP. Consistent with this finding, decreasing the level of ATP by arsenate treatment causes drug tolerance. Lowering ATP slows translation and prevents the formation of DNA double-strand breaks upon fluoroquinolone treatment. We conclude that variation in ATP levels leads to persister formation by decreasing the activity of antibiotic targets.

IMPORTANCE Persisters are a subpopulation of antibiotic-tolerant cells responsible for the recalcitrance of chronic infections. Our current understanding of persister formation is primarily based on studies of E. coli. The activation of toxin-antitoxin systems by ppGpp has become a widely accepted model for persister formation. In this study, we found that stress-induced activation of mRNA interferase-type toxins does not necessarily cause persister formation. We also found that the persister marker rrnB P1 reports persister cells because it detects a drop in cellular ATP levels. Consistent with this, lowering the ATP level decreases antibiotic target activity and, thus, leads to persister formation. We conclude that stochastic variation in ATP is the main mechanism of persister formation. A decrease in ATP provides a satisfactory explanation for the drug tolerance of persisters, since bactericidal antibiotics act by corrupting energy-dependent targets.

ABSTRACT

Bacteria adopt social behavior to expand into new territory, led by specialized swarmers, before forming a biofilm. Such mass migration of Bacillus subtilis on a synthetic medium produces hyperbranching dendrites that transiently (equivalent to 4 to 5 generations of growth) maintain a cellular monolayer over long distances, greatly facilitating single-cell gene expression analysis. Paradoxically, while cells in the dendrites (nonswarmers) might be expected to grow exponentially, the rate of swarm expansion is constant, suggesting that some cells are not multiplying. Little attention has been paid to which cells in a swarm are actually multiplying and contributing to the overall biomass. Here, we show in situ that DNA replication, protein translation and peptidoglycan synthesis are primarily restricted to the swarmer cells at dendrite tips. Thus, these specialized cells not only lead the population forward but are apparently the source of all cells in the stems of early dendrites. We developed a simple mathematical model that supports this conclusion.

IMPORTANCE Swarming motility enables rapid coordinated surface translocation of a microbial community, preceding the formation of a biofilm. This movement occurs in thin films and involves specialized swarmer cells localized to a narrow zone at the extreme swarm edge. In the B. subtilis system, using a synthetic medium, the swarm front remains as a cellular monolayer for up to 1.5 cm. Swarmers display high-velocity whirls and vortexing and are often assumed to drive community expansion at the expense of cell growth. Surprisingly, little attention has been paid to which cells in a swarm are actually growing and contributing to the overall biomass. Here, we show that swarmers not only lead the population forward but continue to multiply as a source of all cells in the community. We present a model that explains how exponential growth of only a few cells is compatible with the linear expansion rate of the swarm.

Lipid-mediated signaling events regulate many cellular processes. Investigations of the complex underlying mechanisms are difficult because several different methods need to be used under varying conditions. Here we introduce multifunctional lipid derivatives to study lipid metabolism, lipid−protein interactions, and intracellular lipid localization with a single tool per target lipid. The...

Lipophilic teicoplanin pseudoaglycon derivatives are active against vancomycin- and teicoplanin-resistant enterococci

The Journal of Antibiotics advance online publication, February 1 2017. doi:10.1038/ja.2017.2

Authors: Zsolt Szűcs, Ilona Bereczki, Magdolna Csávás, Erzsébet Rőth, Anikó Borbás, Gyula Batta, Eszter Ostorházi, Réka Szatmári & Pál Herczegh

ABSTRACT

The blood-brain barrier (BBB) protects the central nervous system (CNS) by restricting the passage of molecules and microorganisms. Despite this barrier, however, the fungal pathogen Cryptococcus neoformans invades the brain, causing a meningoencephalitis that is estimated to kill over 600,000 people annually. Cryptococcal infection begins in the lung, and experimental evidence suggests that host phagocytes play a role in subsequent dissemination, although this role remains ill defined. Additionally, the disparate experimental approaches that have been used to probe various potential routes of BBB transit make it impossible to assess their relative contributions, confounding any integrated understanding of cryptococcal brain entry. Here we used an in vitro model BBB to show that a "Trojan horse" mechanism contributes significantly to fungal barrier crossing and that host factors regulate this process independently of free fungal transit. We also, for the first time, directly imaged C. neoformans-containing phagocytes crossing the BBB, showing that they do so via transendothelial pores. Finally, we found that Trojan horse crossing enables CNS entry of fungal mutants that cannot otherwise traverse the BBB, and we demonstrate additional intercellular interactions that may contribute to brain entry. Our work elucidates the mechanism of cryptococcal brain invasion and offers approaches to study other neuropathogens.

IMPORTANCE The fungal pathogen Cryptococcus neoformans invades the brain, causing a meningoencephalitis that kills hundreds of thousands of people each year. One route that has been proposed for this brain entry is a Trojan horse mechanism, whereby the fungus crosses the blood-brain barrier (BBB) as a passenger inside host phagocytes. Although indirect experimental evidence supports this intriguing mechanism, it has never been directly visualized. Here we directly image Trojan horse transit and show that it is regulated independently of free fungal entry, contributes to cryptococcal BBB crossing, and allows mutant fungi that cannot enter alone to invade the brain.

<i>Bacillus subtilis</i> biofilm extends <i>Caenorhabditis elegans</i> longevity through downregulation of the insulin-like signalling pathway

Nature Communications, Published online: 30 January 2017; doi:10.1038/ncomms14332

Probiotic bacteria can improve host health, but the mechanisms underlying such beneficial effects are often unclear. Here, the authors show that biofilm formation of the probiotic bacterium B. subtilis extends the lifespan of its host, the nematode C. elegans, by reducing insulin-like signalling.

Lactate racemase is the first enzyme known to possess a metal pincer active site. The enzyme interconverts d- and l-lactic acid, which is important for the assembly of cell walls in many microorganisms. Here, we report a synthetic model of the active site of lactate racemase, which features a pyridinium-based...