Structure and Function of Sterols in Fungi

Weete, John D.

doi:10.1016/b978-0-12-024923-7.50007-8

Cited by 138 publications

(81 citation statements)

References 178 publications

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“…Although ergosterol is the predominant sterol in many fungi, sterols other than ergosterol have been reported (36). A recent study suggested that there is a high degree of sequence homology between P. carinii and P. polycephalum on the basis of their 5S RNA sequences (35).…”

Section: Resultsmentioning

confidence: 99%

“…Many lower fungi are incapable of de novo sterol synthesis (36). If P. carinii is incapable of sterol synthesis, the concentration of sterols in the lung microenvironment could conceivably affect the growth of the organism in at least two ways: (i) cholesterol could fulfill bulk sterol requirements and the concentrations of cholesterol in the lung microenvironment may regulate the growth of the organism, or (ii) the sterols found in coinfecting fungi or other microorganisms could have a regulatory effect on the growth of the organism (36). It is clear that the regulation of the sterol content of P. carinii is important for understanding the growth of the organism.…”

Section: Resultsmentioning

confidence: 99%

“…Because plant and fungal sterols are often similar, both types are sometimes referred to as phytosterols. A differentiating feature of the sterols of plants, protozoa, and fungi is the side chain configuration at C-24 which separates the algae and fungi from the vascular plants (36). Other lipids have been described in microorganisms that are not present in mammalian cells and could provide clues to phylogeny.…”

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confidence: 99%

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Phytosterols are present in Pneumocystis carinii

Furlong

Samia

Rose

et al. 1994

Antimicrob Agents Chemother

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Although originally classified as a protozoan, Pneumocystis carinii is now considered to have fungal characteristics. Drugs typically used for the treatment of fungal infections target ergosterol. Because P. carinii is an important pathogen in AIDS and other immunocompromised patients, knowledge of the sterol content of this organism may be useful as a basis for developing new treatment strategies or for improving diagnosis. P. carinii organisms were harvested from infected rat lungs and were purified by filtration. Control preparations from uninfected animals were identically prepared. Lipids were extracted from the organisms and control preparations and were separated into neutral lipid, glycolipid, and phospholipid fractions by silicic acid chromatography. The neutral lipid fraction was further treated by alkaline hydrolysis and was analyzed by reversed-phase high-pressure liquid chromatography (HPLC), gas chromatography (GC), and GC-mass spectrometry (GC-MS). As shown by HPLC, the neutral lipid fraction from infected rats contained a minimum of six peaks, while in control preparations a single peak with a retention time identical to that of cholesterol was observed. The predominant sterol in these preparations was positively identified by GC-MS as cholesterol and constituted 80 to 90% of the total. The remaining peaks had relative retention times similar to those of phytosterols by both HPLC and GC, and the similarity of these sterols to those derived from plants and fungi was confirmed by MS. Ergosterol, however, was not present. These results provide further evidence for a close phylogenetic relationship between P. carinii and fungi and suggest that these sterols could be used as targets for drug development and for improving diagnosis.Pneumocystis carinii is one of the leading causes of opportunistic infection in AIDS patients (30). Despite the importance of this microorganism as an opportunistic pathogen, much basic information about the parasite is lacking. While originally classified phylogenetically as a protozoan, analyses of P. carinii DNA and mitochondrial and rRNA sequences have generally shown a higher degree of homology to the mitochondrial and rRNA sequences of fungi (yeasts) than to those of protozoa (9,13,27,31,34,35). The exact relationship remains to be determined. Analyses of 5S RNA have suggested a somewhat close phylogenetic relationship to members of the Rhizopoda-Myxomycota-Zygomycota group of "protista fungi." Other studies have suggested similarities to Saccharomyces, Candida, and Neurospora spp. and "red yeast" fungi. In general, the arguments in favor of classifying P. carinii as a protozoan are the amoeboid appearance of the trophic form, susceptibility to antiprotozoal drugs such as pentamidine isethionate or trimethoprim-sulfamethoxazole, insusceptibility to antifungal drugs such as amphotericin B, and the lack of ergosterol in Pneumocystis cell membranes. Arguments in favor of including P. carinii among the fungi include similarities of the sporogenous state to ascospore format...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Phytosterols are present in Pneumocystis carinii

Furlong

Samia

Rose

et al. 1994

Antimicrob Agents Chemother

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“…several alternative metabolic pathways leading to ergosterol in fungi, all result in the incorporation of 12 carbon atoms derived from the radiolabeled carboxyl group (C-l) of the acetate molecule (Weete 1989). The amount of ergosterol produced during incubations with radiolabel can therefore be directly derived from the number of incorporated acetate molecules.…”

Section: Discussionmentioning

confidence: 99%

Growth and production of aquatic hyphomycetes in decomposing leaf litter

Gessner

Chauvet

1997

Limnol. Oceanogr.

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The acetate-to-ergosterol technique was used to estimate fungal productivity of three species of aquatic hyphomycetes growing in decomposing ash leaves in stream microcosms. Following a lag of 20-88 min, incorporation of acetate into ergosterol was linear for at least 10 h. Substrate saturation was reached in the mM range, and there was no indication of isotope dilution. For one species, Articulospora tetracladia, a conversion factor of 5.5 mg mycelial dry mass produced per pmol acetate incorporated was deter-mined. This was similar to the theoretical conversion factor (6.6 mg p,mol-I) deduced from pathways OF ergosterol synthesis in fungi. Thus, the acetate-toergosterol assay appears to be suitable for estimating the productivity of aquatic hyphomycetes growing in leaf litter in streams. Estimated growth rates of A. tetracladia in microcosms changed markedly over time, with the maximum being as high as 0.72 d-l at an early growth stage. After 23 d when 58% of the initial leaf mass was degraded, the fungus had produced 89 mg biomass per g of initial leaf mass. Almost half of this production was allocated to conidia. Assuming an average growth efficiency of 0.35, this would be equivalent to a fungal assimilation of 25% of initial leaf mass and account for 44% of the observed leaf mass loss. In an experiment with leaf litter colonized by fungi in a stream, acetate incorporation was linear for 6 h, but the estimated growth rate was only 0.017 d-l.

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“…Mass loss and fungal biomass dynamics Mass loss of wood in the nylon bags was calculated as the difference in dry weight between fresh and incubated woody fragments and is expressed as a percentage of the original mass. Ergosterol, a sterol only found in fungal cell membranes (Weete 1989), was used as a fungal-specific biomarker and extraction from wood samples was conducted according to methodology of Bååth (2001) for soil samples. Wood (0.25 g) of each sample was added to 1 ml cyclohexane and 4 ml 10% KOH in methanol.…”

Section: Soil and Samplingmentioning

confidence: 99%

Initial decay of woody fragments in soil is influenced by size, vertical position, nitrogen availability and soil origin

et al. 2007

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Fast-growing bacteria and fungi are expected to cause the initial stage of decomposition of woody fragments in and on soils, i.e. the respiration of sugars, organic acids, pectin and easily accessible cellulose and hemi-cellulose. However, little is known about the factors regulating initial wood decomposition. We examined the effect of wood fragment size, vertical position, nitrogen addition and soil origin on initial wood decay and on the relative importance of fungi and bacteria therein. Two fractions of birch wood were used in microcosm experiments, namely wood blocks (dimensions: 3×0.5×0.5 cm) and sawdust (dimensions: 0.5-2 mm). The woody fragments were enclosed in nylon bags and placed on top of-or buried in an abandoned arable soil and in a heathland soil. After 15, 25 and 40 weeks of incubation, fungal biomass was quantified (as ergosterol and chitin content) and bacterial numbers were determined. The results indicated that initial wood decay was mostly caused by fungi; bacteria were only contributing in sawdust in/on abandoned arable soil. Larger fragment size, burial of fragments and nitrogen addition positively influenced fungal biomass and activity. Fungal biomass and decay activities were much lower in woody fragments incubated in/on heathland soil than in those incubated in/on abandoned arable soil, indicating that soil origin is also an important factor determining initial wood decay.

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Structure and Function of Sterols in Fungi

Cited by 138 publications

References 178 publications

Phytosterols are present in Pneumocystis carinii

Phytosterols are present in Pneumocystis carinii

Growth and production of aquatic hyphomycetes in decomposing leaf litter

Initial decay of woody fragments in soil is influenced by size, vertical position, nitrogen availability and soil origin

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