The Zygomycetes in a Phylogenetic Perspective
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Persoonia 30, 2013: i–iv www.ingentaconnect.com/content/nhn/pimj INTRODUCTION http://dx.doi.org/10.3767/003158513X666277 The zygomycetes in a phylogenetic perspective Zygomycetes surround us in our daily life, not only as agents of an exchange of ideas, and providing an updated view on this disease, but also as starters of fermentation in the preparation group of fungi. The outcome of this meeting formed the basis of food products, and as pioneer degraders in food spoilage. of the present special issue of Persoonia. Since many members grow easily in axenic culture and show Zygomycetes are among the most ancient fungi, and we aim to an impressive morphology, they have been subject of studies present a general overview of their impressive diversity. Start- since the mid nineteenth century. Recent progress in whole ing with Krings et al. we provide insight into the fossil records genome sequencing projects aim to determine genetic features of this fascinating group of fungi. We take a closer look at the in genomic terms, such as their remarkable ability to pioneer largest order, the Mucorales, of which Walther et al. present a on virgin substrates before competing microorganisms arrive. comprehensive molecular overview, Lu et al. describe a very Although they exhibit a wide variety of different lifestyles includ- remarkable representative of the order and Hoffmann et al. give ing hyperparasitism and endosaprotrophy, many aspects of their an overview of family structures. Wagner et al. direct attention ecology are still poorly understood. This diverse ecology may to the phylogeny of Mortierellales and Grygansky et al. present explain their changing faces: assisting humanity already over a phylogenetic overview of the Entomophthorales. Dealing with thousands of years in preparing our food, but also their relent- the problems of resolving the backbone in the fungal tree (see less aggression towards the weakened human host. below), Tretter et al. evaluate the usefulness of some new loci During recent years zygomycetes have emerged as agents of for the resolution of basic lineages, particularly in the Kickxel- disease in hospitalized patients. Presumably this is partly due lomycetales. to prophylaxis against Aspergillus fumigatus, which reduces the frequency of Aspergillus infections, and sees Mucorales fill a Zygomycetes as agents of infection window of opportunity. Infections by species of Mucorales such as Lichtheimia, Mucor and Rhizopus may be highly mutilating Undoubtedly, the greater majority of fungi in the zygomycete in patients with severe leukemia, transplants, with ketoacidotic amalgamate do not possess any virulence to mammals what- diabetes, or as agents of wound infections. Extended necrosis soever. In clinical practice, the term ‘zygomycosis’ actually of tissue frequently leads to death in the susceptible patient stands for infections by members of only three out of the 13 population. The emergence of mucoralean fungi as agents orders known, viz. the Mucorales, the Entomophthorales and of disease has resulted in a renewed global interest in zygo- the Mortierellales. Interestingly, pathologies observed in the mycetes. The present issue of Persoonia reflects the growing three orders have hardly anything in common. Especially significance of this group of fungi. the syndromes of Mucorales and Entomophthorales in many ways are each other’s opposite. Infections by Lichtheimia or Zygomycete research in the scientific community is presently Rhizopus in the Mucorales typically are acute, which seems to stimulated and coordinated on an international basis by the ECMM-ISHAM (European Confederation of Medical Mycology, be an expression of their pioneer ecology mentioned above. and International Society for Human and Animal Mycology) Angiotropism leads to rapid clotting of blood veins and extended Working Group Zygomycoses, co-ordinated by George Petrik- tissue necrosis – with the enigmatic Mucor irregularis as the kos. The Working Group was founded in 2004 under ECMM. only exception (Li & Lun 2012). Infections by Basidiobolus or After organizing the 1st International Forum on Zygomycosis Conidiobolus in the Entomophthorales, however, are typically in 2008 at Cape Sounion, Greece, a supplement of Clinical chronic, with hyphal elements residing in affected tissue over Microbiology and Infection was published. A second Forum lengthy periods of time, leading to deposition of antigenic was held in 2010 at Porto Heli, Greece. A website was made material around the fungus. The syndromes of Mucorales and in the same year (www.zygomyco.net) with a database where Entomophthorales in many ways are each other’s opposite. cases of mucormycosis can be submitted online. An overview of Do ‘zygomycetes’ exist at all, and can patients suffer from ‘zy- zygomycosis in Europe was published with 230 cases accrued gomycoses’? In an influential paper, Hibbett et al. (2007) noted by the registry of the Working Group (Skiada et al. 2011). The that the backbone of the phylogenetic tree of fungi traditionally Working Group joined ISHAM in 2009. Several members of the united in the phylum ‘Zygomycota’ was not resolved, and thus group took part in a meeting in Chicago, organized by Thomas that they do not compose a natural entity. The polyphyletic Walsh with the support of the Hank Schueler foundation and zygomycota should be abandoned, and hence the term ‘zygo- a special issue of Clinical Infectious Diseases was published mycosis’ can no longer be applied for an infection caused by a (Walsh & Kontoyannis 2012). Subsequently a Special Inter- member of that group. Disease names referring to the ordinal est Group (SIG) meeting was organized by Kerstin Voigt and level would therefore be more informative than ‘zygomycosis’. Sybren de Hoog in conjunction with the International Mycologi- ‘Entomophthoromycosis’ is available for infections caused by cal Congress on the Biology of Fungi (IMC9) held in Edinburgh, members of the Entomophthorales, while for those by Muco- Scotland, August 2010. A follow-up meeting concentrating on rales the term ‘mucoralomycosis’ would be logical. Although zygomycete biodiversity took place in Utrecht, the Netherlands, formally incorrect, the use of the more commonly used term March 2011. This meeting enabled fruitful discussions, inspiring ‘mucormycosis’ is advocated (Kwon-Chung 2012). © 2013 Naturalis Biodiversity Center & Centraalbureau voor Schimmelcultures You are free to share - to copy, distribute and transmit the work, under the following conditions: Attribution: You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). Non-commercial: You may not use this work for commercial purposes. No derivative works: You may not alter, transform, or build upon this work. For any reuse or distribution, you must make clear to others the license terms of this work, which can be found at http://creativecommons.org/licenses/by-nc-nd/3.0/legalcode. Any of the above conditions can be waived if you get permission from the copyright holder. Nothing in this license impairs or restricts the author’s moral rights. ii Persoonia – Volume 30, 2013 Taxonomic dilemmas at species level and above phylogenetic trees are subject to change, and this situation will With the recent technical improvements, molecular phylogeny is certainly remain for the next decades at least, when poorly rolling over old concepts (Schoch et al. 2012). With taxonomies sampled habitats such as the intestinal tracts of amphibians, becoming more detailed, we observe a significant degree of or drowned mosquitos in Siberian lakes have exhaustively rank inflation in the former zygomycetes. Many of the groups been sampled. that classically were treated as orders, such as the Kickxellales Species delimitations in zygomycetous fungi on the basis of or Zoopagales, today are raised to the status of the separate the biological species concept may be problematic when ascer- subphyla Kickxellomycotina and Zoopagomycotina. Some of tained by mating experiments. Successful sexual interaction is a these higher-level taxa contain only a very few species. Phy- prime criterion to verify whether the high degrees of intraspecific logenetically they are among the basal lineages of the fungal variation observed in some of the fungi concerned truly match kingdom, a position ascribed to their early evolution in the his- with species delimitations. However, sexual vigour may differ tory of life on earth (Berbee & Taylor 1993). By calibration of between strains, some being highly competent, showing re- phylogenetic trees using fossil records with known geological sponse outside species limits. Alastruey-Izquierdo et al. (2010) age the ancestry of the zygomycetous groups was determined observed zygospores between two suspensors, which just were to lie at least a billion years back. Orders that are considered smaller in shape and lighter in colour than those resulting from to be the most recent are roughly dated at 250 million years intraspecific mating. Geneological coalescence in silico may (Hoffmann et al. 2013). This implies that during times when therefore be a more reproducible criterion to establish levels higher ascomycetes started to emerge, the zygomycetous fungi of intraspecific variation. Albeit difficult to define, the species were already fully adapted, and had successfully occupied is the only significant taxonomic category in fungi, because their habitats. In many ways they seem to have remained un-