Table of contents

Volume 3, Issue 7, pp. 263 - 301, July 2016

Issue cover
Cover: Microscopic image of the edge of a Candida albicans colony, a dimorphic yeast that can live either as blastospores or as hyphae. In this issue, Laprade et al. report that C. albicans hyphal cells are more resistant to programmed cell death than their blastopore cell counterparts. Image by Melissa Brown, Morgan McCarty, and Nicanor Austriaco, O.P. (Providence College, U.S.A.); modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license. Enlarge issue cover

Reviews

Evidence for the hallmarks of human aging in replicatively aging yeast

Georges E. Janssens, Liesbeth M. Veenhoff

page 263-274 | 10.15698/mic2016.07.510 | Full text | PDF | Abstract

Recently, efforts have been made to characterize the hallmarks that accompany and contribute to the phenomenon of aging, as most relevant for humans [1]. Remarkably, studying the finite lifespan of the single cell eukaryote budding yeast (recently reviewed in [2] and [3]) has been paramount for our understanding of aging. Here, we compile observations from literature over the past decades of research on replicatively aging yeast to highlight how the hallmarks of aging in humans are present in yeast. We find strong evidence for the majority of these, and summarize how yeast aging is especially characterized by the hallmarks of genomic instability, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, and mitochondrial dysfunction.

Research Articles

Cox1 mutation abrogates need for Cox23 in cytochrome c oxidase biogenesis

Richard Dela Cruz, Mi-Young Jeong and Dennis R. Winge

page 275-284 | 10.15698/mic2016.07.511 | Full text | PDF | Abstract

Cox23 is a known conserved assembly factor for cytochrome c oxidase, although its role in cytochrome c oxidase (CcO) biogenesis remains unresolved. To gain additional insights into its role, we isolated spontaneous suppressors of the respiratory growth defect in cox23∆ yeast cells. We recovered independent colonies that propagated on glycerol/lactate medium for cox23∆ cells at 37°C. We mapped these mutations to the mitochondrial genome and specifically to COX1 yielding an I101F substitution. The I101F Cox1 allele is a gain-of-function mutation enabling yeast to respire in the absence of Cox23. CcO subunit steady-state levels were restored with the I101F Cox1 suppressor mutation and oxygen consumption and CcO activity were likewise restored. Cells harboring the mitochondrial genome encoding I101F Cox1 were used to delete genes for other CcO assembly factors to test the specificity of the Cox1 mutation as a suppressor of cox23∆ cells. The Cox1 mutant allele fails to support respiratory growth in yeast lacking Cox17, Cox19, Coa1, Coa2, Cox14 or Shy1, demonstrating its specific suppressor activity for cox23∆ cells.

Research Reports

Filamentation protects Candida albicans from amphotericin B-induced programmed cell death via a mechanism involving the yeast metacaspase, MCA1

David J. Laprade, Melissa S. Brown, Morgan L. McCarthy, James J. Ritch, and Nicanor Austriaco

page 285-292 | 10.15698/mic2016.07.512 | Full text | PDF | Abstract

The budding yeast Candida albicans is one of the most significant fungal pathogens worldwide. It proliferates in two distinct cell types: blastopores and filaments. Only cells that are able to transform from one cell type into the other are virulent in mouse disease models. Programmed cell death is a controlled form of cell suicide that occurs when C. albicans cells are exposed to fungicidal drugs like amphotericin B and caspofungin, and to other stressful conditions. We now provide evidence that suggests that programmed cell death is cell-type specific in yeast: Filamentous C. albicans cells are more resistant to amphotericin B- and caspofungin-induced programmed cell death than their blastospore counterparts. Finally, our genetic data suggests that this phenomenon is mediated by a protective mechanism involving the yeast metacaspase, MCA1.

Microreviews

Inhibition of Zika virus by Wolbachia in Aedes aegypti

Eric Pearce Caragata, Heverton Leandro Carneiro Dutra, Luciano Andrade Moreira

page 293-295 | 10.15698/mic2016.07.513 | Full text | PDF | Abstract

Through association with cases of microcephaly in 2015, Zika virus (ZIKV) has transitioned from a relatively unknown mosquito-transmitted pathogen to a global health emergency, emphasizing the need to improve existing mosquito control programs to prevent future disease outbreaks. The response to Zika must involve a paradigm shift from traditional to novel methods of mosquito control, and according to the World Health Organization should incorporate the release of mosquitoes infected with the bacterial endosymbiont Wolbachia pipientis. In our recent paper [Dutra, HLC et al., Cell Host & Microbe 2016] we investigated the potential of Wolbachia infections in Aedes aegypti to restrict infection and transmission of Zika virus recently isolated in Brazil. Wolbachia is now well known for its ability to block or reduce infection with a variety of pathogens in different mosquito species including the dengue (DENV), yellow fever, and chikungunya viruses, and malaria-causing Plasmodium, and consequently has great potential to control mosquito-transmitted diseases across the globe. Our results demonstrated that the wMel Wolbachia strain in Brazilian Ae. aegypti is a strong inhibitor of ZIKV infection, and furthermore appears to prevent transmission of infectious viral particles in mosquito saliva, which highlights the bacterium’s suitability for more widespread use in Zika control.

Antibiotic use in childhood alters the gut microbiota and predisposes to overweight

Katri Korpela and Willem M de Vos

page 296-298 | 10.15698/mic2016.07.514 | Full text | PDF | Abstract

A correlation between the use of antibiotics in early life and the excessive weight gain in later childhood has been shown in several large cohort studies all over the world. One hypothesis explaining this association is the pervasive impact that antibiotics may have on the intestinal microbiota, and this has been supported by recent mouse studies. Studies have shown dramatic changes in the intestinal microbiota of adults in response to oral antibiotic treatments. However, little is known about the impact of antibiotics on the intestinal microbiota of children, although antibiotics account for the majority of the medication prescribed to children in Western countries.

House of cellulose – a new hideout for drug tolerant Mycobacterium tuberculosis

Ashwani Kumar

page 299-301 | 10.15698/mic2016.07.515 | Full text | PDF | Abstract

Mycobacterium tuberculosis (Mtb) causes tuberculosis (TB). The treatment of TB requires administration of multiple drugs for long durations because of the unusual drug tolerance of Mtb. The phenotypic drug tolerance of genetically drug-susceptible Mtb in humans can be explained by its ability to form biofilms. Recent studies from different laboratories suggest that Mtb forms biofilms that harbour drug-tolerant bacteria. These findings have created a new area of research in the field of mycobacterial physiology. Recently, my laboratory has reported that Mtb cells organise themselves into biofilms in response to intracellular thiol reductive stress (Trivedi et al. Nature communications. 2016). Bacteria residing in these biofilms are tolerant towards antimycobacterial drugs. Cellulose is a key component of the extracellular polymeric substances that hold mycobacterial cells together in these biofilms. Here, I discuss the implications of these findings and new hypotheses arising from this study on the biology of Mtb biofilms.