''Purpureocillium lilacinum'' is a species of filamentous

fungus A fungus ( : fungi or funguses) is any member of the 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, separately from t ...

in the family Ophiocordycipitaceae. It has been isolated from a wide range of habitats, including cultivated and uncultivated

soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

grassland A grassland is an area where the vegetation is dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...

, deserts, 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 The rhizosphere is the narrow region of soil or substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome. Soil pores in the rhizosphere can contain many bacteria and other microo ...

of many crops. The species can grow at a wide range of temperatures – from for a few isolates, with optimal growth in the range . 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 Root-knot nematodes are plant-parasitism, parasitic nematodes from the genus ''Meloidogyne''. They exist in soil in areas with hot climates or short winters. About 2000 plants worldwide are susceptible to infection by root-knot nematodes and they ...

Taxonomy and phylogeny

The species was originally described by American mycologist

Charles Thom Charles Thom (November 11, 1872 – May 24, 1956) was an American microbiologist and mycology, mycologist. Born and raised in Illinois, he received his PhD from the University of Missouri, the first such degree awarded by that institution. He w ...

in 1910, under than name ''Penicillium lilacinum''. Taxonomic synonyms include ''Penicillium amethystinum'' Wehmer and ''Spicaria rubidopurpurea'' Aoki. In 1974, Robert A. Samson transferred the species to ''

Paecilomyces ''Paecilomyces'' is a genus of fungi. A number of species in this genus are plant pathogens. Several of the entomopathogenic species, such as "''Paecilomyces fumosoroseus''" have now been placed in the genus '' Isaria'': in the order Hypocreale ...

''. Publications in the 2000s (decade) indicated that the genus ''

'' 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.

Description

''Purpureocillium lilacinum'' forms a dense mycelium which gives rise to

conidiophores A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to ...

. 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 , 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 hyphae 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.

Chlamydospore A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as '' Candida'', Basidiomycota such as '' Panus'', and various Mortierellales species. It is the life-stage which survives in unfavourable ...

s 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 entomopathogenic, mycoparasitic,

saprophytic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ( ...

, as well as nematophagous.

Human pathogenicity

''Purpureocillium lilacinum'' is an infrequent cause of human disease. Most reported cases involve patients with compromised

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...

s, indwelling foreign devices, or

intraocular lens Intraocular lens (IOL) is a lens (optics), lens implanted in the human eye, eye as part of a treatment for cataracts or myopia. If the natural lens is left in the eye, the IOL is known as Phakic intraocular lens, phakic, otherwise it is a pseudop ...

implants. Research of the last decade suggests it may be an emerging pathogen of both immunocompromised as well as immunocompetent adults.Carey J, D’Amico R, Sutton DA, Rinaldi MG. Paecilomyces lilacinus vaginitis in an immunocompetent patient. Emerg Infect Dis [serial online] 2003 Sep
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Biocontrol agent

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 An environmental hazard is a substance, state or event which has the potential to threaten the surrounding natural environment or adversely affect people's health, including pollution and natural disasters such as storms and earthquakes. It can i ...

, high costs, limited availability in many developing countries or their diminished effectiveness following repeated applications.

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 incognita ''Meloidogyne incognita'' (root-knot nematode - RKN), also known as the "southern root-nematode" or "cotton root-knot nematode" is a plant-parasitic roundworm in the family Heteroderidae. This nematode is one of the four most common species world ...

'' in

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...

. 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 A field trial is a competitive event for gundogs. Field trials are conducted for pointing dogs and setters, retrievers and spaniels, with each assessing the different types various working traits. In the United States, field trials are also co ...

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 others, 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

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

s produced by ''P. lilacinum'' have been studied. A basic

serine protease Serine proteases (or serine endopeptidases) are enzymes that cleave peptide bonds in proteins. Serine serves as the nucleophilic amino acid at the (enzyme's) active site. They are found ubiquitously in both eukaryotes and prokaryotes. Seri ...

with biological activity against '' Meloidogyne hapla'' eggs has been identified. One strain of ''P. lilacinum'' has been shown to produce

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...

s and a

chitinase Chitinases (EC 3.2.1.14, chitodextrinase, 1,4-β-poly-N-acetylglucosaminidase, poly-β-glucosaminidase, β-1,4-poly-N-acetyl glucosamidinase, poly ,4-(N-acetyl-β-D-glucosaminide)glycanohydrolase, (1→4)-2-acetamido-2-deoxy-β-D-glucan glycano ...

, 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 This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...

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 hypha, 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

and to grow towards adjacent eggs.

Mycotoxins

Paecilotoxin is a mycotoxin isolated from the fungus. Its significance is unknown. Khan et al. (2003) tested one strain of ''P. lilacinum'' for the production of paecilotoxin and were unable to show toxin production in that strain, suggesting that toxin synthesis may vary among isolates.

References

External links

* * {{taxonbar, from=Q55724157 Ophiocordycipitaceae Biopesticides Biotechnology Biological pest control Fungi described in 1910 Taxa named by Charles Thom