Current Issue:

Table of contents

Volume 4, Issue 11, pp. 365 - 389, November 2017

Issue cover
Cover: This photomicrograph features a chorazol black-stained specimen, revealing the presence of a cyst of the parasitic organism, Entamoeba histolytica. This mature cyst contains the characteristic four nuclei, as well as a darkly-staining chromatoid body (image by Dr. Libero Ajello, Center for Disease Control and Prevention, USA and obtained via the CDC Public Health Image Library , ID#3785); image modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license. Enlarge issue cover

Editorial

Uncovering the hidden: complexity and strategies for diagnosing latent tuberculosis

Mario Alberto Flores-Valdez

page 365-367 | 10.15698/mic2017.11.596 | Full text | PDF | Abstract

Tuberculosis produces two clinical manifestations: active and latent (non-apparent) disease. The latter is estimated to affect one-third of the world population and constitutes a source of continued transmission should the disease emerge from its hidden state (reactivation). Methods to diagnose latent TB have been evolving and aim to detect the disease in people who are truly infected with M. tuberculosis, versus those where other mycobacteria, or even other pathologies not related to TB, are present. The current use of proteomic and transcriptomic approaches may lead to improved detection methods in the coming years.

Reviews

The integrated stress response in budding yeast lifespan extension

Spike D.L. Postnikoff, Jay E. Johnson and Jessica K. Tyler

page 368-375 | 10.15698/mic2017.11.597 | Full text | PDF | Abstract

Aging is a complex, multi-factorial biological process shared by all living organisms. It is manifested by a gradual accumulation of molecular alterations that lead to the decline of normal physiological functions in a time-dependent fashion. The ultimate goal of aging research is to develop therapeutic means to extend human lifespan, while reducing susceptibility to many age-related diseases including cancer, as well as metabolic, cardiovascular and neurodegenerative disorders. However, this first requires elucidation of the causes of aging, which has been greatly facilitated by the use of model organisms. In particular, the budding yeast Saccharomyces cerevisiae has been invaluable in the identification of conserved molecular and cellular determinants of aging and for the development of approaches to manipulate these aging determinants to extend lifespan. Strikingly, where examined, virtually all means to experimentally extend lifespan result in the induction of cellular stress responses. This review describes growing evidence in yeast that activation of the integrated stress response contributes significantly to lifespan extension. These findings demonstrate that yeast remains a powerful model system for elucidating conserved mechanisms to achieve lifespan extension that are likely to drive therapeutic approaches to extend human lifespan and healthspan.

Research Articles

Cross-species complementation of bacterial- and eukaryotic-type cardiolipin synthases

Petra Gottier, Mauro Serricchio, Rita Vitale, Angela Corcelli, and Peter Bütikofer

page 376-383 | 10.15698/mic2017.11.598 | Full text | PDF | Abstract

The glycerophospholipid cardiolipin is a unique constituent of bacterial and mitochondrial membranes. It is involved in forming and stabilizing high molecular mass membrane protein complexes and in maintaining membrane architecture. Absence of cardiolipin leads to reduced efficiency of the electron transport chain, decreased membrane potential, and, ultimately, impaired respiratory metabolism. For the protozoan parasite Trypanosoma brucei cardiolipin synthesis is essential for survival, indicating that the enzymes involved in cardiolipin production represent potential drug targets. T. brucei cardiolipin synthase (TbCLS) is unique as it belongs to the family of phospholipases D (PLD), harboring a prokaryotic-type cardiolipin synthase (CLS) active site domain. In contrast, most other eukaryotic CLS, including the yeast ortholog ScCrd1, are members of the CDP-alcohol phosphatidyl­ transferase family. To study if these mechanistically distinct CLS enzymes are able to catalyze cardiolipin production in a cell that normally expresses a different type of CLS, we expressed TbCLS and ScCrd1 in CLS-deficient yeast and trypanosome strains, respectively. Our results show that TbCLS complemented cardiolipin production in CRD1 knockout yeast and partly restored wild-type colony forming capability under stress conditions. Remarkably, CL remodeling appeared to be impaired in the transgenic construct, suggesting that CL production and remodeling are tightly coupled processes that may require a clustering of the involved proteins into specific CL-synthesizing domains. In contrast, no complementation was observed by heterologous expression of ScCrd1 in conditional TbCLS knockout trypanosomes, despite proper mitochondrial targeting of the protein.

Microreviews

Breaking the bad: Bacillus blocks fungal virulence factors

François L. Mayer and James W. Kronstad

page 384-386 | 10.15698/mic2017.11.599 | Full text | PDF | Abstract

Fungal pathogens rely on the production of specific virulence factors during infection. Inhibiting such factors generally results in reduced fungal pathogenicity. Most studies in the past have focused on understanding the molecular mechanisms of fungal virulence factor expression during mono-culture, or during interaction with the host. However, a potentially important, second type of interaction has been less well studied thus far – the interplay of fungal pathogens of humans with other microbes found in their natural habitat. Specifically, whether environmental bacteria may impact fungal virulence factor production is largely unknown. In our recent work, we have identified the soil bacterium, Bacillus safensis, as a potent inhibitor of virulence factor production by two major fungal pathogens of humans, Cryptococcus neoformans, and Candida albicans. We determined that the anti-virulence factor mechanism is, at least in part, based on production of bacterial chitinases that target and destabilize the fungal cell surface. These findings describe a cross-kingdom interaction between an environmental bacterium and pathogenic fungi, and highlight the fungal cell wall as an attractive antifungal drug target.

Shutdown of interferon signaling by a viral-hijacked E3 ubiquitin ligase

Kaitlin A. Davis and John T. Patton

page 387-389 | 10.15698/mic2017.11.600 | Full text | PDF | Abstract

Viruses manipulate cellular processes to create an environment favorable to replication. For most viruses, this includes subverting the expression of interferon (IFN), a signaling molecule that can stimulate production of a vast array of antiviral gene products. Rotavirus, a segmented double-stranded RNA virus that causes acute gastroenteritis in infants and young children, inhibits IFN expression through its nonstructural protein NSP1. This viral protein stifles IFN expression by inducing the degradation of host factors that are necessary for upregulating the activity of IFN genes. In the case of nearly all human and porcine rotavirus strains, NSP1 induces the ubiquitination-dependent proteasomal degradation of β-transducin repeat containing protein (β-TrCP), a host factor that plays an essential role in activating the IFN-transcription factor, NF-κB. Key to the process is the presence of a decoy sequence (degron) at the C-terminus of NSP1 that causes β-TrCP to mistakenly bind NSP1 instead of its natural target, inhibitor-of-κB (IκB). In a recent report published by Davis et al [2017; mBio 8(4): e01213-17], we describe molecular requirements that govern NSP1 recognition of β-TrCP, including an essential degron phosphorylation event, and the step-wise incorporation of NSP1 into hijacked cullin-RING E3 ligases (CRLs) that ubiquitinate and tag β-TrCP for degradation. Notably, although β-TrCP is chiefly recognized for its role as a master regulator of NF-κB signaling and IFN expression, β-TrCP also controls the stability of checkpoint proteins implicated in numerous other cellular pathways with antiviral activities, including autophagy and apoptosis. Thus, the impact of NSP1 on creating an intracellular environment favorable to virus replication may extend well beyond the IFN signaling pathway.