Purpureocillium
Encyclopedia
Purpureocillium is a fungal genus
in the Ophiocordycipitaceae
family. The genus is monotypic
, containing the single species Purpureocillium lilacinum, a common saprobic, filamentous fungus
. It has been isolated from a wide range of habitats including cultivated and uncultivated soil
s, forest
s, grassland
, desert
s, estuarine
sediments and sewage sludge, and insects. It has also been found in nematode
eggs, and occasionally from females of root-knot and cyst nematodes. In addition, it has frequently been detected in the rhizosphere
of many crops. The species can grow at a wide range of temperatures – from 8 to 38 °C (46.4 to 100.4 F) for a few isolates, with optimal growth in the range 26 to 30 °C (78.8 to 86 F). It also has a wide pH
tolerance and can grow on a variety of substrates. P. lilacinum has shown promising results for use as a biocontrol agent
to control the growth of destructive root-knot nematodes.
. Publications in the 2000s indicated that the genus Paecilomyces
was not monophyletic, and that close relatives were Paecilomyces nostocoides, Isaria takamizusanensis and Nomuraea atypicola. The new genus Purpureocillium was created to hold the taxon. The generic name refers to the purple conidia produced by the fungus.
Purpureocillium lilacinum used to be classified with the Fungi Imperfecti or Deuteromycetes, fungi for which perfect (i.e., sexually reproducing) states have rarely been found. Paecilomyces lilacinum was classified in the section Isarioidea, for which perfect states have not been found. Many isolates of P. lilacinum have been identified from around the world and it is accepted that variation exists within the species. Phylogenetic analysis of P. lilacinum isolates show that it is more closely related to Trichoderma
, Gliocladium and Hypocrea
than to the other entomopathogenic Paecilomyces species in the Hypocreales.
which gives rise to conidiophores
. These bear phialides from the ends of which spores are formed in long chains. Spores germinate when suitable moisture and nutrients are available. Colonies on malt agar grow rather fast, attaining a diameter of 5–7 cm within 14 days at 25 °C (77 °F), consisting of a basal felt with a floccose overgrowth of aerial mycelium
; at first white, but when sporulating changing to various shades of vinaceous. The reverse side is sometimes uncolored but usually in vinaceous shades. The vegetative hypha
e are smooth-walled, hyaline
, and 2.5–4.0 µm
wide. Conidiophores arising from submerged hyphae, 400–600 µm in length, or arising from aerial hyphae and half as long. Phialides consisting of a swollen basal part, tapering into a thin distinct neck. Conidia
are in divergent chains, ellipsoid to fusiform in shape, and smooth walled to slightly roughened. Chlamydospores
are absent.
, mycoparasitic, saprophytic, as well as nematophagous
.
s, indwelling foreign devices, or intraocular lens
implants. Research of the last decade suggests it may be an emerging pathogen of both immunocompromised as well as immunocompetent adults.
Plant-parasitic nematodes cause significant economic losses to a wide variety of crops. Chemical control is a widely used option for plant-parasitic nematode management. However, chemical nematicides are now being reappraised in respect of environmental hazard, high costs, limited availability in many developing countries or their diminished effectiveness following repeated applications.
in Peru
. It has now been isolated from many cyst and root-knot nematodes and from soil in many locations. Several successful field trials using P. lilacinum against pest nematodes were conducted in Peru. The Peruvian isolate was then sent to nematologists in 46 countries for testing, as part of the International Meloidogyne project, resulting in many more field trial
s on a range of crops in many soil types and climates. Field trials, glasshouse trials and in vitro testing of P. lilacinum continues and more isolates have been collected from soil, nematodes and occasionally from insects. Isolates vary in their pathogenicity to plant-parasitic nematodes. Some isolates are aggressive parasites while other, though morphologically indistinguishable, are less or non-pathogenic. Sometimes isolates that looked promising in vitro or in glasshouse trials have failed to provide control in the field.
s produced by P. lilacinum have been studied. A basic serine protease
with biological activity against Meloidogyne hapla eggs has been identified. One strain of P. lilacinum has been shown to produce protease
s and a chitinase
, enzymes that could weaken a nematode egg shell so as to enable a narrow infection peg to push through.
, closely appressed to the eggshell. Adhesion between the appressorium and nematode egg surface must be strong enough to withstand the opposing force produced by the extending tip of a penetration hypha. When the hypha has penetrated the egg, it rapidly destroys the juvenile within, before growing out of the now empty egg shell to produce conidiophores and to grow towards adjacent eggs.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
in the Ophiocordycipitaceae
Ophiocordycipitaceae
The Ophiocordycipitaceae are a family of fungi in the Ascomycota, class Sordariomycetes.-Genera:*Elaphocordyceps*Haptocillium*Harposporium*Hirsutella*Hymenostilbe*Ophiocordyceps*Paraisaria*Purpureocillium...
family. The genus is monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
, containing the single species Purpureocillium lilacinum, a common saprobic, filamentous fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
. It has been isolated from a wide range of habitats including cultivated and uncultivated soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s, forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
s, grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
, desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
s, estuarine
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
sediments and sewage sludge, and insects. It has also been found in nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
eggs, and occasionally from females of root-knot and cyst nematodes. In addition, it has frequently been detected in the rhizosphere
Rhizosphere
The rhizosphere is the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms. Soil which is not part of the rhizosphere is known as bulk soil. The rhizosphere contains many bacteria that feed on sloughed-off plant cells, termed rhizodeposition, and...
of many crops. The species can grow at a wide range of temperatures – from 8 to 38 °C (46.4 to 100.4 F) for a few isolates, with optimal growth in the range 26 to 30 °C (78.8 to 86 F). It also has a wide pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
tolerance and can grow on a variety of substrates. P. lilacinum has shown promising results for use as a biocontrol agent
Biological pest control
Biological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
to control the growth of destructive root-knot nematodes.
Taxonomy and phylogeny
The species was originally described by American mycologist Charles Thom in 1910, under than name Penicillium lilacinum. Taxonomic synonyms include Penicillium amethystinum Wehmer and Spicaria rubidopurpurea Aoki. In 1974, Charles Thom transferred the species to PaecilomycesPaecilomyces
Paecilomyces is a genus of nematophagous fungus which kills harmful nematodes by pathogenesis, causing disease in the nematodes. Therefore the fungus can be used as a bio-nematicide to control nematodes by applying it to soil.-Species:...
. Publications in the 2000s indicated that the genus Paecilomyces
Paecilomyces
Paecilomyces is a genus of nematophagous fungus which kills harmful nematodes by pathogenesis, causing disease in the nematodes. Therefore the fungus can be used as a bio-nematicide to control nematodes by applying it to soil.-Species:...
was not monophyletic, and that close relatives were Paecilomyces nostocoides, Isaria takamizusanensis and Nomuraea atypicola. The new genus Purpureocillium was created to hold the taxon. The generic name refers to the purple conidia produced by the fungus.
Purpureocillium lilacinum used to be classified with the Fungi Imperfecti or Deuteromycetes, fungi for which perfect (i.e., sexually reproducing) states have rarely been found. Paecilomyces lilacinum was classified in the section Isarioidea, for which perfect states have not been found. Many isolates of P. lilacinum have been identified from around the world and it is accepted that variation exists within the species. Phylogenetic analysis of P. lilacinum isolates show that it is more closely related to Trichoderma
Trichoderma
Trichoderma is a genus of fungi that is present in all soils, where they are the most prevalent culturable fungi. Many species in this genus can be characterized as opportunistic avirulent plant symbionts.-Species:...
, Gliocladium and Hypocrea
Hypocrea
Hypocrea is a genus of fungi in the Hypocreaceae family. The widespread genus is estimated to contain 171 species that grow on rotten wood, and are often associated with other fungi. Anamorphic genera associated with Hypocrea include Acremonium, Gliocladium, Trichoderma, and Verticillium...
than to the other entomopathogenic Paecilomyces species in the Hypocreales.
Description
Purpureocillium lilacinum forms a dense myceliumMycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
which gives rise to conidiophores
Conidium
Conidia, sometimes termed conidiospores, are asexual, non-motile spores of a fungus and are named after the greek word for dust, konia. They are also called mitospores due to the way they are generated through the cellular process of mitosis...
. These bear phialides from the ends of which spores are formed in long chains. Spores germinate when suitable moisture and nutrients are available. Colonies on malt agar grow rather fast, attaining a diameter of 5–7 cm within 14 days at 25 °C (77 °F), consisting of a basal felt with a floccose overgrowth of aerial mycelium
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
; at first white, but when sporulating changing to various shades of vinaceous. The reverse side is sometimes uncolored but usually in vinaceous shades. The vegetative hypha
Hypha
A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...
e are smooth-walled, hyaline
Hyaline
The term hyaline denotes a substance with a glass-like appearance.-Histopathology:In histopathological medical usage, a hyaline substance appears glassy and pink after being stained with haematoxylin and eosin — usually it is an acellular, proteinaceous material...
, and 2.5–4.0 µm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
wide. Conidiophores arising from submerged hyphae, 400–600 µm in length, or arising from aerial hyphae and half as long. Phialides consisting of a swollen basal part, tapering into a thin distinct neck. Conidia
Conidium
Conidia, sometimes termed conidiospores, are asexual, non-motile spores of a fungus and are named after the greek word for dust, konia. They are also called mitospores due to the way they are generated through the cellular process of mitosis...
are in divergent chains, ellipsoid to fusiform in shape, and smooth walled to slightly roughened. Chlamydospores
Chlamydospore
A Chlamydospore is the thick-walled big resting spore of several kinds of fungi. It is the life-stage which survives in unfavourable conditions, such as dry or hot seasons....
are absent.
Life cycles
Purpureocillium lilacinum is highly adaptable in its life strategy: depending on the availability of nutrients in the surrounding microenvironments it may be entomopathogenicEntomopathogenic fungus
An entomopathogenic fungus is a fungus that can act as a parasite of insects and kills or seriously disables them.-Typical life cycle:These fungi usually attach to the external body surface of insects in the form of microscopic spores...
, mycoparasitic, saprophytic, as well as nematophagous
Nematophagous fungus
Nematophagous fungi are carnivorous fungi specialized in trapping and digesting nematodes. Around 160 species are known. There exist both species that live inside the nematodes from the beginning and others that catch them mostly with glue traps or in rings, some of which constrict on contact. Some...
.
Human pathogenicity
Purpureocillium lilacinum is an infrequent cause of human disease. Most reported cases involve patients with compromised immune systemImmune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
s, indwelling foreign devices, or intraocular lens
Intraocular lens
An intraocular lens is an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract, or as a form of refractive surgery to change the eye's optical power. It usually consists of a small plastic lens with plastic side struts, called...
implants. Research of the last decade suggests it may be an emerging pathogen of both immunocompromised as well as immunocompetent adults.
Biocontrol agent
Control of plant-parasitic nematodes
Purpureocillium lilacinum was first observed in association with nematode eggs in 1966 and the fungus was subsequently found parasitising the eggs of Meloidogyne incognitaMeloidogyne incognita
The Meloidogyne incognita is a nematode, a type of roundworm, in the family Heteroderidae. It is an important plant parasite classified in parasitology as a root-knot nematode, as it prefers to attack the root of its host plant....
in Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
. It has now been isolated from many cyst and root-knot nematodes and from soil in many locations. Several successful field trials using P. lilacinum against pest nematodes were conducted in Peru. The Peruvian isolate was then sent to nematologists in 46 countries for testing, as part of the International Meloidogyne project, resulting in many more field trial
Field trial
A field trial is a competitive event at which hunting dogs compete against one another. There are field trials for retrievers, pointing dogs and flushing dogs. Field trials are usually organized by kennel clubs or other gun dog organizations...
s on a range of crops in many soil types and climates. Field trials, glasshouse trials and in vitro testing of P. lilacinum continues and more isolates have been collected from soil, nematodes and occasionally from insects. Isolates vary in their pathogenicity to plant-parasitic nematodes. Some isolates are aggressive parasites while other, though morphologically indistinguishable, are less or non-pathogenic. Sometimes isolates that looked promising in vitro or in glasshouse trials have failed to provide control in the field.
Enzymes
Many enzymeEnzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s produced by P. lilacinum have been studied. A basic serine protease
Serine protease
Serine proteases are enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the active site.They are found ubiquitously in both eukaryotes and prokaryotes...
with biological activity against Meloidogyne hapla eggs has been identified. One strain of P. lilacinum has been shown to produce protease
Protease
A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....
s and a chitinase
Chitinase
Chitinases are hydrolytic enzymes that break down glycosidic bonds in chitin. As chitin is a component of the cell walls of fungi and exoskeletal elements of some animals , chitinases are generally found in organisms that either need to reshape their own chitin or dissolve and digest the chitin of...
, enzymes that could weaken a nematode egg shell so as to enable a narrow infection peg to push through.
Egg infection
Before infecting a nematode egg, P. lilacinum flattens against the egg surface and becomes closely appressed to it. P. lilacinum produces simple appressoria anywhere on the nematode egg shell either after a few hyphae grow along the egg surface, or after a network of hyphae form on the egg. The presence of appressoria appears to indicate that the egg is, or is about to be, infected. In either case, the appressorium appears the same, as a simple swelling at the end of a hyphaHypha
A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...
, closely appressed to the eggshell. Adhesion between the appressorium and nematode egg surface must be strong enough to withstand the opposing force produced by the extending tip of a penetration hypha. When the hypha has penetrated the egg, it rapidly destroys the juvenile within, before growing out of the now empty egg shell to produce conidiophores and to grow towards adjacent eggs.