Malassezia and Human Skin Diseases: Difference between revisions

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=Introduction=
=Introduction=


"Malassezia" is a genus of organisms under the kingdom of fungi that exist in mycelial and yeast forms [[#References|[1]]]. These organisms have a lipid layer encircling their cell walls and have thicker cell walls than most yeast [[#References|[1]]] . Most known species of "Malassezia" are lipid-dependent and many are part of the human [http://en.wikipedia.org/wiki/Human_microbiome normal flora] [[#References|[2]]] . Such species can be found in sebum-rich areas of the skin and are linked to skin diseases such as pityriasis versicolor, "Malassezia folliculitis", dandruff and seborrhoiec dermatitis [[#References|[2]]] .  
''Malassezia'' is a genus of organisms under the kingdom of fungi that exist in mycelial and yeast forms [[#References|[1]]]. These organisms have a lipid layer encircling their cell walls and have thicker cell walls than most yeast [[#References|[1]]] . Most known species of ''Malassezia'' are lipid-dependent and many are part of the human [http://en.wikipedia.org/wiki/Human_microbiome normal flora] [[#References|[2]]] . Such species can be found in sebum-rich areas of the skin and are linked to skin diseases such as pityriasis versicolor, ''Malassezia'' folliculitis, dandruff and seborrhoiec dermatitis [[#References|[2]]].  


=Current Species=


There are three officially recognized ''Ignicoccus''  species: ''Ignicoccus hospitalis'' , '' Ignicoccus pacificus '' and '' Ignicoccus islandicus'' . The three species were initially identified by 16S rRNA gene analysis from the hydrothermal vent samples obtained from Kolbeinsey Ridge and the coast of Mexico[[#References|[1]]] . All three species have been characterized as hyperthermophiles that are also [http://en.wikipedia.org/wiki/Obligate_anaerobe obligate anaerobes] which explains the presence of ''Ignicoccus'' species near hydrothermal vents[[#References|[1]]] . None of the members of the ''Ignicoccus''  genus have been found to be [http://en.wikipedia.org/wiki/Pathogenic] pathogenic to humans.
=Metabolism=
 
=Morphology=


The members of the ''Ignicoccus'' genus are motile irregular coccoid cells that range in diameter from 1 to 3 µm. The motility observed is due to the presence of flagella, but unfortunately the polarity of the flagella is not yet fully elucidated. They are known to have an outer-membrane but no [http://en.wikipedia.org/wiki/S-layer S-layer]. This is a novel characteristic for these [http://en.wikipedia.org/wiki/Archaea Archaea] because''Ignicoccus'' are the only known Archaea that have been shown to possess an outer-membrane[[#References|[2]]] [[#References|[10]]] .  
In 1939, it was first recognized that ''Malassezia'' species required lipid uptake for growth [[#References|[1]]]. The need for a lipid-rich environment is consistent with the localization of ''Malassezia'' species on sebum-rich parts of the human body. Human sebum is a substance secreted by [http://en.wikipedia.org/wiki/Sebaceous_gland sebaceous glands] and is found in high levels on the skin of the face, scalp and upper trunk [[#References|[1]]]. It plays an important role in maintaining the epidermal permeability barrier and has many other related roles [[#References|[3]]]. Sebaceous gland activity is highest from puberty on, and declines after the third decade and it also correlates with incidence of scalp scaling [[#References|[3]]]. Sebum mainly contains triglycerides, esters and fatty acids [[#References|[3]]]. ''Malassezia globosa'' was shown to metabolize triglycerides in an artificial sebum and consequently produce free fatty acids [[#References|[3]]]. These results are demonstrated in Figure 1. The products of the lipid metabolism of ''Malassezia'' species are unsaturated fatty acids and saturated fatty acids and the latter are consumed to induce proliferation of ''Malassezia'' [[#References|[3]]].


[[File:Huber-abb2.jpg|300px|thumb|left| Ultrathin section of an ''Ignicoccus hospitalis'' cell.]]
The need for a lipid-rich environment was revealed through sequencing of mRNA transcripts of ''Malassezia'' species. It was found that ''M. globosa'' expresses genes necessary for the processes of glycolysis, TCA cycle, amino acid synthesis and nucleic acid base synthesis but there was an obvious absence of genes encoding [http://en.wikipedia.org/wiki/Fatty_acid_synthase fatty acid synthases] [[#References|[2]]]. This explains the need for an external source of fatty acids [[#References|[2]]]. In addition, secreted [http://en.wikipedia.org/wiki/Lipase lipases] play an important role in ''Malassezia'' species because they are needed to degrade triglycerides of the human sebum into free fatty acids [[#References|[4]]]. Such lipases have been isolated and purified from the human scalp, one of which is produced from the lipase gene LIP1 [[#References|[4]]].




==Outer-Membrane==
=Pathogenesis=


The outer-membrane of ''Ignicoccus'' species was found to be composed of various derivatives of the typical lipid [http://en.wikipedia.org/wiki/Archaeol archaeol], including the derivative known as [http://en.wikipedia.org/wiki/Caldarchaeol caldarchaeol] [[#References|[5]]] . The outer-membrane is dominated by a pore composed of the Imp1227 protein (''Ignicoccus'' outer membrane protein 1227). The Imp1227 protein forms a large nonamer ring with a predicted pore size of 2nm[[#References|[7]]] .
Although ''Malassezia'' species are [http://en.wikipedia.org/wiki/Commensalism commensal] organisms of the normal flora, they are associated with skin diseases mainly due to the production of unsaturated fatty acids through their degradation of lipids [[#References|[4]]]. It was demonstrated that oleic acid, an unsaturated fatty acid and product of ''Malassezia'' species metabolism, induces flaking of the scalp in dandruff susceptible individuals [[#References|[5]]]. This is shown in Figure 2 where oleic acid is administered to the human scalp of one group and compared to a placebo group for differences in flaking from the baseline. Individual susceptibility is also an important aspect of the pathogenesis of ''Malassezia'' species because scalp flaking was not observed on oleic acid-induced scalps of non-susceptible individuals [[#References|[5]]]. Additionally, another unsaturated fatty acid metabolite of ''Malassezia'' species is arachidonic acid and it is involved in promoting inflammation [[#References|[1]]]. A depiction of the metabolism of ''Malassezia'' species and the consequences of their resulting metabolites is shown in Figure 3.  


=Metabolism=


''Ignicoccus'' species are [http://en.wikipedia.org/wiki/Chemolithoautotroph chemolithoautotrophs] that use molecular hydrogen as the inorganic electron donor and elemental sulphur as the inorganic terminal electron acceptor[[#References|[1]]] . The reduction of the elemental sulphur results in the production of hydrogen sulphide gas.
=Immunomodulation=


''Ignicoccus'' are autotrophs in that they fix their own carbon dioxide into organic molecules. The carbon dioxide fixation process they use is a novel process called [http://www.pnas.org/content/105/22/7851.full a dicarboxylate/4-hydroxybutyrate autotrophic carbon assimilation cycle] that involves 14 different enzymes[[#References|[8]]] .  
''Malassezia'' seem to play a paradoxical role in modulating immune responses by both promoting and down regulating the immune system [[#References|[1]]]. One study demonstrates that ''Malassezia'' species are capable of up-regulating the production of reactive oxygen intermediates such as hydrogen peroxide, superoxide and hydroxyl radical by [http://en.wikipedia.org/wiki/Macrophages macrophages], which enhances the killing of intracellular bacteria [[#References|[6]]]. However, another study shows that ''Malassezia'' suppresses the secretion of [http://en.wikipedia.org/wiki/Pro-inflammatory_cytokine pro-inflammatory cytokines] including IL-6, IL-1β and TNF-α [[#References|[7]]]. This was further studied to show that the lipid component of ''Malassezia'' cell walls directly induces this down regulation thus making it an essential component to the commensal state of the organism [[#References|[8]]].


Members of the ''Ignicoccus''  genus are able to use ammonium as a nitrogen source.


==Growth Conditions==
=Associated Diseases=
 
Because members of the ''Ignicoccus''  genus are [http://en.wikipedia.org/wiki/Hyperthermophile hyperthermophiles] and obligate anaerobes, it is not surprising that their growth conditions are very complex. They are grown in a liquid medium known as ½ SME ''Ignicoccus''  which is a solution of synthetic sea water which is then made anaerobic.
 
Grown in this media at their optimal growth temperature of 90C, the members of the ''Ignicoccus''  genus typically reach a cell density of ~4x107cells/mL[[#References|[1]]] .
 
The addition of [http://en.wikipedia.org/wiki/Yeast_extract yeast extract] to the ½ SME media has been shown to stimulate the growth and increase maximum cell density achieved. The mechanism by which this is achieved is not known[[#References|[1]]] .


The following diseases are shown to be associated with ''Malassezia'' but no causal link has been shown between the listed diseases and their associated organisms [[#References|[3]]].
Pitiryasis Versicolor: This disease is associated with the mycelial form of ''Malassezia'' species and is characterized by pigmented lesions on the upper trunk [[#References|[9]]]. It is also characterized by tissue inflammation and tissue invasion by the organisms [[#References|[10]]].


=Symbiosis=
''Malassezia'' Foliculitis: This condition is characterized by an inflammatory rash on the upper trunk and is associated with ''M. globosa'' [[#References|[10]]].


''Ignicoccus hospitalis''  is the only member of the genus ''Ignicoccus'' that has been shown to have an extensive [http://en.wikipedia.org/wiki/Symbiosis symbiotic relationship] with another organism.
Seborrhoiec dermatitis/Dandruff: There is an ongoing debate over whether or not these two conditions are separate, or if dandruff is just a milder form of seborrhoiec dermatitis [[#References|[1]]]. Both diseases involve scaling and inflammation of sebum rich skin, mainly on the scalp [[#References|[1]]]. There is no evidence of tissue invasion in hair follicle biopsies of affected individuals [[#References|[10]]].


''Ignicoccus hospitalis''  has been shown to engage in symbiosis with ''Nanoarchaeum equitans'' . ''Nanoarchaeum equitans''  is a very small coccoid species with a cell diameter of 0.4 µm[[#References|[9]]] . Genome analysis has provided much of the known information about this species.


To further complicate the symbiotic relationship between both species, it’s been observed that the presence of ''Nanoarchaeum equitans''  on the surface of ''Ignicoccus hospitalis''  somehow inhibits the cell replication of ''Ignicoccus hospitalis'' . How or why this occurs has not yet been elucidated[[#References|[3]]] .
=Therapy=


[[File:Urzwerg.jpg|300px|thumb|right| ''Ignicoccus hospitalis'' with two attached  ''Nanoarchaeum equitans'' cells.]]
Antifungals have been used as effective treatment against the aforementioned diseases [[#References|[11]]].  [http://en.wikipedia.org/wiki/Zinc_pyrithione Zinc pyrithione] is shown to effectively treat dandruff and seborrhoiec dermatitis [[#References|[9]]]. ''Malassezia'' species are also susceptible to [http://en.wikipedia.org/wiki/Azole azole drugs] including voriconazole, ketoconazole and itraconazole [[#References|[11]]]. The main issue with these antifungal therapies, however, is that the ''Malassezia'' genus comprises a heterogeneous group of species that can vary in their susceptibility to these drugs [[#References|[11]]].


[[File:IhNeRelationship2 jpeg.jpg|250px|thumb|left| Epifluoroscence micrographs of an ''Ignicoccus hospitalis''and ''Nanoarchaeum equitans'' coculture stained with BacLight at various time points. Living cells stain green while dead cells stain red. (A) Exponential growth phase 3.25 hours after inoculation. (B) Transition into the stationary phase 7.5 hours after inoculation. (C) Stationary phase 10 hours after inoculation. (D) Stationary phase 23 hours after inoculation.]]


=Current Research=


==''Nanoarchaeum equitans''==
There is ongoing research being done on ''Malassezia'' species due to the relevance of these organisms to skin diseases. Further research into which species of ''Malassezia'' are responsible for certain conditions is currently underway in order to find more specific treatments to these conditions [[#References|[9]]]. Also, the proposal of a topical treatment, which would alter the lipid composition of affected skin, is a current area of research in controlling ''Malassezia''-associated diseases [[#References|[9]]].


''Nanoarchaeum equitans'' has the smallest non-viral genome ever sequenced at 491kb[[#References|[9]]] . Analysis of the genome sequence indicates that 95% of the predicted proteins and stable RNA molecules are somehow involved in repair and replication of the cell and its genome[[#References|[3]]] .


Analysis of the genome also showed that ''Nanoarchaeum equitans''  lacks nearly all genes known to be required in amino acid, nucleotide, cofactor and lipid metabolism. This is partially supported by the evidence that ''Nanoarchaeum equitans''  has been shown to derive its cell membrane from its host ''Ignicoccus hospitalis''  cell membrane. The direct contact observed between ''Nanoarchaeum equitans'' and ''Ignicoccus hospitalis''  is hypothesized to form a pore between the two organisms in order to exchange metabolites or substrates (likely from ''Ignicoccus hospitalis''  towards ''Nanoarchaeum equitans'' due to the parasitic relationship). The exchange of periplasmic vesicles is not thought to be involved in metabolite or substrate exchange despite the presence of vesicles in the periplasm of ''Ignicoccus hospitalis'' .
These analyses of the ''Nanoarchaeum equitans'' genome support the fact of the extensive symbiotic relationship between ''Nanoarchaeum equitans'' and ''Ignicoccus hospitalis''. However, it has not yet been proven that it is a strictly parasitic relationship and further research may prove that there is a commensal relationship between the two species.
=References=
=References=


Revision as of 05:01, 26 November 2013

This student page has not been curated.

Introduction

Malassezia is a genus of organisms under the kingdom of fungi that exist in mycelial and yeast forms [1]. These organisms have a lipid layer encircling their cell walls and have thicker cell walls than most yeast [1] . Most known species of Malassezia are lipid-dependent and many are part of the human normal flora [2] . Such species can be found in sebum-rich areas of the skin and are linked to skin diseases such as pityriasis versicolor, Malassezia folliculitis, dandruff and seborrhoiec dermatitis [2].


Metabolism

In 1939, it was first recognized that Malassezia species required lipid uptake for growth [1]. The need for a lipid-rich environment is consistent with the localization of Malassezia species on sebum-rich parts of the human body. Human sebum is a substance secreted by sebaceous glands and is found in high levels on the skin of the face, scalp and upper trunk [1]. It plays an important role in maintaining the epidermal permeability barrier and has many other related roles [3]. Sebaceous gland activity is highest from puberty on, and declines after the third decade and it also correlates with incidence of scalp scaling [3]. Sebum mainly contains triglycerides, esters and fatty acids [3]. Malassezia globosa was shown to metabolize triglycerides in an artificial sebum and consequently produce free fatty acids [3]. These results are demonstrated in Figure 1. The products of the lipid metabolism of Malassezia species are unsaturated fatty acids and saturated fatty acids and the latter are consumed to induce proliferation of Malassezia [3].

The need for a lipid-rich environment was revealed through sequencing of mRNA transcripts of Malassezia species. It was found that M. globosa expresses genes necessary for the processes of glycolysis, TCA cycle, amino acid synthesis and nucleic acid base synthesis but there was an obvious absence of genes encoding fatty acid synthases [2]. This explains the need for an external source of fatty acids [2]. In addition, secreted lipases play an important role in Malassezia species because they are needed to degrade triglycerides of the human sebum into free fatty acids [4]. Such lipases have been isolated and purified from the human scalp, one of which is produced from the lipase gene LIP1 [4].


Pathogenesis

Although Malassezia species are commensal organisms of the normal flora, they are associated with skin diseases mainly due to the production of unsaturated fatty acids through their degradation of lipids [4]. It was demonstrated that oleic acid, an unsaturated fatty acid and product of Malassezia species metabolism, induces flaking of the scalp in dandruff susceptible individuals [5]. This is shown in Figure 2 where oleic acid is administered to the human scalp of one group and compared to a placebo group for differences in flaking from the baseline. Individual susceptibility is also an important aspect of the pathogenesis of Malassezia species because scalp flaking was not observed on oleic acid-induced scalps of non-susceptible individuals [5]. Additionally, another unsaturated fatty acid metabolite of Malassezia species is arachidonic acid and it is involved in promoting inflammation [1]. A depiction of the metabolism of Malassezia species and the consequences of their resulting metabolites is shown in Figure 3.


Immunomodulation

Malassezia seem to play a paradoxical role in modulating immune responses by both promoting and down regulating the immune system [1]. One study demonstrates that Malassezia species are capable of up-regulating the production of reactive oxygen intermediates such as hydrogen peroxide, superoxide and hydroxyl radical by macrophages, which enhances the killing of intracellular bacteria [6]. However, another study shows that Malassezia suppresses the secretion of pro-inflammatory cytokines including IL-6, IL-1β and TNF-α [7]. This was further studied to show that the lipid component of Malassezia cell walls directly induces this down regulation thus making it an essential component to the commensal state of the organism [8].


Associated Diseases

The following diseases are shown to be associated with Malassezia but no causal link has been shown between the listed diseases and their associated organisms [3].

Pitiryasis Versicolor: This disease is associated with the mycelial form of Malassezia species and is characterized by pigmented lesions on the upper trunk [9]. It is also characterized by tissue inflammation and tissue invasion by the organisms [10].

Malassezia Foliculitis: This condition is characterized by an inflammatory rash on the upper trunk and is associated with M. globosa [10].

Seborrhoiec dermatitis/Dandruff: There is an ongoing debate over whether or not these two conditions are separate, or if dandruff is just a milder form of seborrhoiec dermatitis [1]. Both diseases involve scaling and inflammation of sebum rich skin, mainly on the scalp [1]. There is no evidence of tissue invasion in hair follicle biopsies of affected individuals [10].


Therapy

Antifungals have been used as effective treatment against the aforementioned diseases [11]. Zinc pyrithione is shown to effectively treat dandruff and seborrhoiec dermatitis [9]. Malassezia species are also susceptible to azole drugs including voriconazole, ketoconazole and itraconazole [11]. The main issue with these antifungal therapies, however, is that the Malassezia genus comprises a heterogeneous group of species that can vary in their susceptibility to these drugs [11].


Current Research

There is ongoing research being done on Malassezia species due to the relevance of these organisms to skin diseases. Further research into which species of Malassezia are responsible for certain conditions is currently underway in order to find more specific treatments to these conditions [9]. Also, the proposal of a topical treatment, which would alter the lipid composition of affected skin, is a current area of research in controlling Malassezia-associated diseases [9].


References

(1) Ashbee R, Evans G. 2002. Immunology of Diseases Associated with Malassezia Species. Clin Microbiol Rev. 15: 21–57

(2) Dawson, T. 2007. Malassezia globosa and restricta: Breakthrough Understanding of the Etiology and Treatment of Dandruff and Seborrheic Dermatitis through Whole-Genome Analysis. J. Investig. Dermatol. Symp. Proc. 12:15-19

(3) Ro B, Dawson T. 2005. The Role of Sebaceous Gland Activity and Scalp Microfloral Metabolism in the Etiology of Seborrheic Dermatitis and Dandruff. J. Investig. Dermatol. Symp. Proc. 10:194-197

(4) DeAngelis Y. 2007. Isolation and Expression of a Malassezia globosa Lipase Gene, LIP1. J. Investig. Dermatol. Symp. Proc. 127: 2138-2146

(5) DeAngelis Y, Gemmer C, Kaczvinsky J, Kenneally D, Schwartz J, Dawson T. 2005. Three etiologic facets of dandruff and seborrheic dermatitis: Malassezia fungi, sebaceous lipids, and individual sensitivity. J. Investig. Dermatol. Symp. Proc. 10:295-297

(6) Takahashi M, Ushijima T, Ozaki Y. 1986. Biological activity of Pityrosporum. II. Antitumour and immune stimulating effect of Pityrosporum in mice. J. Natl. Cancer Inst. 77:1093–1097

(7) Kesavan, S., C. E. Walters, K. T. Holland, and E. Ingham. 1998. The effects of Malassezia on pro-inflammatory cytokine production by human peripheral blood mononuclear cells in vitro. Med. Mycol. 36:97–106

(8) Kesavan, S., K. T. Holland, and E. Ingham. 2000. The effect of lipid extraction on the immunomodulatory activity of Malassezia species in vitro. Med. Mycol. 38:239–247

(9) Gupta A, Batra R, Bluhm R, Boekhout T, Dawson L. 2004. Skin diseases associated with Malassezia species. J. Am. Acad. Dermatol. 51:785-798

(10) Hay R. 2011. Malassezia, dandruff and seborrhoeic dermatitis: an overview. Br. J. Dermatol. 165:2-8

(11) Gupta A, Kohil Y, Li A, Faergemann J, Summerbell R. 2001. In vitro susceptibility of the seven Malassezia species toketoconazole, voriconazole, itraconazole and terbinafine. Br. J. Dermatol. 142:758-765

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