Marcos Pires

Angewandte Chemie International Edition, EarlyView.

ChemBioChem, Volume 19, Issue 12, Page 1196-1196, June 18, 2018.

by Shannon K. Esher, Kyla S. Ost, Maria A. Kohlbrenner, Kaila M. Pianalto, Calla L. Telzrow, Althea Campuzano, Connie B. Nichols, Carol Munro, Floyd L. Wormley Jr., J. Andrew Alspaugh

The human fungal pathogen, Cryptococcus neoformans, dramatically alters its cell wall, both in size and composition, upon entering the host. This cell wall remodeling is essential for host immune avoidance by this pathogen. In a genetic screen for mutants with changes in their cell wall, we identified a novel protein, Mar1, that controls cell wall organization and immune evasion. Through phenotypic studies of a loss-of-function strain, we have demonstrated that the mar1Δ mutant has an aberrant cell surface and a defect in polysaccharide capsule attachment, resulting in attenuated virulence. Furthermore, the mar1Δ mutant displays increased staining for exposed cell wall chitin and chitosan when the cells are grown in host-like tissue culture conditions. However, HPLC analysis of whole cell walls and RT-PCR analysis of cell wall synthase genes demonstrated that this increased chitin exposure is likely due to decreased levels of glucans and mannans in the outer cell wall layers. We observed that the Mar1 protein differentially localizes to cellular membranes in a condition dependent manner, and we have further shown that the mar1Δ mutant displays defects in intracellular trafficking, resulting in a mislocalization of the β-glucan synthase catalytic subunit, Fks1. These cell surface changes influence the host-pathogen interaction, resulting in increased macrophage activation to microbial challenge in vitro. We established that several host innate immune signaling proteins are required for the observed macrophage activation, including the Card9 and MyD88 adaptor proteins, as well as the Dectin-1 and TLR2 pattern recognition receptors. These studies explore novel mechanisms by which a microbial pathogen regulates its cell surface in response to the host, as well as how dysregulation of this adaptive response leads to defective immune avoidance.

T cell-engaging bispecific antibodies (biAbs) present a promising strategy for cancer immunotherapy, and numerous bispecific formats have been developed for retargeting cytolytic T cells toward tumor cells. To explore the therapeutic utility of T cell-engaging biAbs targeting the receptor tyrosine kinase ROR1, which is expressed by tumor cells of various...

Bacteria grow and divide by assembling new material into their surface membranes. Gunasinghe et al. used super-resolution microscopy and in situ crosslinking in live bacterial cells in order to visualize intimate contacts between BAM complexes suggesting a model whereby bacteria use highly organized precincts to drive membrane protein assembly.

Two common signal transduction mechanisms used by bacteria to sense and respond to changing environments are two-component systems (TCSs) and eukaryote-like Ser/Thr kinases and phosphatases (eSTK/Ps). Enterococcus faecalis is a Gram-positive bacterium and a serious opportunistic pathogen that relies on both a TCS and an eSTK/P pathway for intrinsic resistance to cell wall-targeting antibiotics. The TCS consists of a histidine kinase (CroS) and a response regulator (CroR) that become activated upon exposure of cells to cell wall-targeting antibiotics, leading to a modulation of gene expression. The eSTK/P pathway consists of a transmembrane kinase (IreK) and its cognate phosphatase (IreP), which act antagonistically to mediate antibiotic resistance through an unknown mechanism. Because both CroS/R and IreK/P contribute to enterococcal resistance toward cell wall-targeting antibiotics, we hypothesized that these signaling systems are intertwined. To test this hypothesis, we analyzed CroR phosphorylation and CroS/R-dependent gene expression to probe the influence of IreK and IreP on CroS/R signaling. In addition, we analyzed the phosphorylation state of CroS, which revealed the IreK-dependent phosphorylation of a Thr residue important for CroS function. Our results are consistent with a model in which IreK positively influences CroR-dependent gene expression through the phosphorylation of CroS to promote antimicrobial resistance in E. faecalis.

IMPORTANCE Two-component signaling systems (TCSs) and eukaryote-like Ser/Thr kinases (eSTKs) are used by bacteria to sense and adapt to changing environments. Understanding how these pathways are regulated to promote bacterial survival is critical for a more complete understanding of bacterial stress responses and physiology. The opportunistic pathogen Enterococcus faecalis relies on both a TCS (CroS/R) and an eSTK (IreK) for intrinsic resistance to cell wall-targeting antibiotics. We probed the relationship between CroS/R and IreK, revealing the convergence of IreK and the sensor kinase CroS to enhance signaling through CroS/R and increase antimicrobial resistance in E. faecalis. This newly described example of eSTK/TCS convergence adds to our understanding of the signaling networks mediating antimicrobial resistance in E. faecalis.

Antibiotic-resistant bacteria show widespread collateral sensitivity to antimicrobial peptides

Antibiotic-resistant bacteria show widespread collateral sensitivity to antimicrobial peptides, Published online: 24 May 2018; doi:10.1038/s41564-018-0164-0

Multidrug-resistant Escherichia coli have a high frequency of collateral sensitivity to antimicrobial peptides, which may arise from changes in lipopolysaccharide regulation.

The immune system responds vigorously to microbial infection while permitting lifelong colonization by the microbiome. Mechanisms that facilitate the establishment and stability of the gut microbiota remain poorly described. We found that a regulatory system in the prominent human commensal Bacteroides fragilis modulates its surface architecture to invite binding of immunoglobulin A (IgA) in mice. Specific immune recognition facilitated bacterial adherence to cultured intestinal epithelial cells and intimate association with the gut mucosal surface in vivo. The IgA response was required for B. fragilis (and other commensal species) to occupy a defined mucosal niche that mediates stable colonization of the gut through exclusion of exogenous competitors. Therefore, in addition to its role in pathogen clearance, we propose that IgA responses can be co-opted by the microbiome to engender robust host-microbial symbiosis.

Immunogene therapy with fusogenic nanoparticles modulates macrophage response to Staphylococcus aureus

Immunogene therapy with fusogenic nanoparticles modulates macrophage response to <i>Staphylococcus aureus</i>, Published online: 17 May 2018; doi:10.1038/s41467-018-04390-7

In the context of increasing bacterial antibiotic-resistance, gene therapy that targets the immune system to clear infection is a major goal. Here the authors show a silicon based nanosystem that modulates the macrophage response in an in vivo model of Staphylococcal pneumonia.

Identification of a S. aureus virulence factor by activity-based protein profiling (ABPP)

Identification of a <i>S. aureus</i> virulence factor by activity-based protein profiling (ABPP), Published online: 16 May 2018; doi:10.1038/s41589-018-0060-1

ABP profiling identifies uncharacterized S. aureus serine hydrolases, including the surface-localized FphB, which processes lipid ester substrates and is required for infection in vivo. An FphB inhibitor reduces in vivo bacterial load.

A cell-penetrating artificial metalloenzyme regulates a gene switch in a designer mammalian cell

A cell-penetrating artificial metalloenzyme regulates a gene switch in a designer mammalian cell, Published online: 16 May 2018; doi:10.1038/s41467-018-04440-0

Artificial enzymes can be used to elicit reactions in cells. Here, the authors developed such an artificial catalyst combined with a genetic switch, and showed that it was readily taken up by human cells and able to kick off a reaction cascade resulting in the biosynthesis of the desired product.

Although the human gut microbiome plays a prominent role in xenobiotic transformation, most of the genes and enzymes responsible for this metabolism are unknown. Recently, we linked the two-gene ‘cardiac glycoside reductase’ (cgr) operon encoded by the gut Actinobacterium Eggerthella lenta to inactivation of the cardiac medication and plant natural product digoxin. Here, we compared the genomes of 25 E. lenta strains and close relatives, revealing an expanded 8-gene cgr-associated gene cluster present in all digoxin metabolizers and absent in non-metabolizers. Using heterologous expression and in vitro biochemical characterization, we discovered that a single flavin- and [4Fe-4S] cluster-dependent reductase, Cgr2, is sufficient for digoxin inactivation. Unexpectedly, Cgr2 displayed strict specificity for digoxin and other cardenolides. Quantification of cgr2 in gut microbiomes revealed that this gene is widespread and conserved in the human population. Together, these results demonstrate that human-associated gut bacteria maintain specialized enzymes that protect against ingested plant toxins.

Laboratory experiments have uncovered many basic aspects of bacterial physiology and behavior. After the past century of mostly in vitro experiments, we now have detailed knowledge of bacterial behavior in standard laboratory conditions, but only a superficial understanding of bacterial functions and behaviors during human infection. It is well-known that...

Flesh-eating bacteria hijack a pain response that suppresses host defense, and blocking this neuro-immune communication holds potential for treatment.

Designer cells programming quorum-sensing interference with microbes

Designer cells programming quorum-sensing interference with microbes, Published online: 08 May 2018; doi:10.1038/s41467-018-04223-7

Bacterial populations communicate with AI-2 signaling molecules, helping to coordinate biofilm development and other group behaviors. Here the authors design a genetic circuit for mammalian cells that allows them to sense bacterial populations and interfere with quorum communication.

Acinetobacter baumannii—a leading cause of nosocomial infections—has a remarkable capacity to persist in hospital environments and medical devices due to its ability to form biofilms. Biofilm formation is mediated by Csu pili, assembled via the “archaic” chaperone–usher pathway. The X-ray structure of the CsuC-CsuE chaperone–adhesin preassembly complex reveals the basis...

Gut microbes were previously suggested to influence mate preference in Drosophila melanogaster (1). Mate selectivity depended on the microbiota associated with flies after prior generations were maintained on different diets [cornmeal–molasses–yeast (CMY) versus starch] (1). Subsequent studies attempted to repeat these findings with contrasting success (2, 3). We suggest that...

A honeycomb-shaped structure of lignin is a key feature, allowing the precise separation between two cell layers during flower abscission.

Gut microbiomes of wild great apes fluctuate seasonally in response to diet

Gut microbiomes of wild great apes fluctuate seasonally in response to diet, Published online: 03 May 2018; doi:10.1038/s41467-018-04204-w

Microbiota composition fluctuates in response to changes in environmental and lifestyle factors. Here, Hicks et al. show that the faecal microbiota of wild gorillas and chimpanzees is temporally dynamic, with shifts that correlate with seasonal rainfall patterns and periods of high and low frugivory.

Shared strategies for β-lactam catabolism in the soil microbiome

Shared strategies for β-lactam catabolism in the soil microbiome, Published online: 30 April 2018; doi:10.1038/s41589-018-0052-1

A β-lactamase, a novel type of amidase, and the phenylacetic acid catabolon comprise a catabolic pathway, revealed by genomic and transcriptomic analysis, that enables multiple soil bacteria to use β-lactam antibiotics as a carbon source.