Isolation of Diaphorobacter sp. LW2 capable of degrading Phenanthrene and its migration mediated by Pythium ultimum

Phenanthrene, one of the polycyclic aromatic hydrocarbons, is stubborn and persistent and exists widely in petroleum-contaminated soil. Filamentous fungi are good assistants to bacterial transport, by hyphae passing through soil pores and reaching further positions. An isolated bacterial strain, from the contaminated soil of the coking plant, was identified as Diaphorobacter and named LW2, which could use phenanthrene as the only carbon source and energy for its growth. LW2 could degrade phenanthrene in a wide range of pH, temperature and initial concentration. When pH was 6 and 10, the removal rate of phenanthrene was 38.59% and 76.44%, respectively, and the removal rate of phenanthrene was 68.25% at 15 ℃. And LW2 could degrade 86.64% phenanthrene when the initial concentration was 100 mg L-1. The detection of DI-N-octyl phthalate, phthalic acid and p-hydroxybenzoic acid revealed that the strain LW2 metabolised phenanthrene through the phthalic acid pathway. Meanwhile, swimming and swarming test results suggested that LW2 was motile. The auxiliary effect of Pythium ultimum on LW2 migration was assessed. In the presence of Pythium ultimum, LW2 could migrate within the range of centimters by its mycelium, which was also observed by fluorescence microscopy. Meanwhile, the degradation ability of LW2 after the migration was also explored. The results proved that the migration process had no significant effect on its degradation ability, and LW2 still showed good phenanthrene metabolism ability. This study provides more possibilities for the bioremediation of phenanthrene-contaminated soil by screening the degradation bacteria and testing the effect of fungi on its migration.

Potential anti-Pythium insidiosum therapeutics identified through screening of agricultural fungicides

Pythiosis is a life-threatening infectious disease caused by the oomycete Pythium insidiosum. Clinical manifestations of pythiosis include an eye, blood vessel, skin, or gastrointestinal tract infection. Pythiosis has been increasingly reported worldwide, with an overall mortality rate of 28%. Radical surgery is required to save patients' lives due to the limited efficacy of antimicrobial drugs. Effective medical treatments are urgently needed for pythiosis. This study aims to find anti-P. insidiosum agents by screening 17 agricultural fungicides that inhibit plant-pathogenic oomycetes and validating their efficacy and safety. Cyazofamid outperformed other fungicides as it can potently inhibit genetically diverse P. insidiosum isolates while exhibiting minimal cellular toxicities. The calculated therapeutic scores determined that the concentration of cyazofamid causing significant cellular toxicities was eight times greater than the concentration of the drug effectively inhibiting P. insidiosum. Furthermore, other studies showed that cyazofamid exhibits low-to-moderate toxicities in animals. The mechanism of cyazofamid action is likely the inhibition of cytochrome b, an essential component in ATP synthesis. Molecular docking and dynamic analyses depicted a stable binding of cyazofamid to the Qi site of the P. insidiosum's cytochrome b orthologous protein. In conclusion, our search for an effective anti-P. insidiosum drug indicated that cyazofamid is a promising candidate for treating pythiosis. With its high efficacy and low toxicity, cyazofamid is a potential chemical for treating pythiosis, reducing the need for radical surgeries, and improving recovery rates. Our findings could pave the way for the development of new and effective treatments for pythiosis.IMPORTANCEPythiosis is a severe infection caused by Pythium insidiosum. The disease is prevalent in tropical/subtropical regions. This infectious condition is challenging to treat with antifungal drugs and often requires surgical removal of the infected tissue. Pythiosis can be fatal if not treated promptly. There is a need for a new treatment that effectively inhibits P. insidiosum. This study screened 17 agricultural fungicides that target plant-pathogenic oomycetes and found that cyazofamid was the most potent in inhibiting P. insidiosum. Cyazofamid showed low toxicity to mammalian cells and high affinity to the P. insidiosum's cytochrome b, which is involved in energy production. Cyazofamid could be a promising candidate for the treatment of pythiosis, as it could reduce the need for surgery and improve the survival rate of patients. This study provides valuable insights into the biology and drug susceptibility of P. insidiosum and opens new avenues for developing effective therapies for pythiosis.

Altering in vivo membrane sterol composition affects the activity of the cyclic lipopeptides tolaasin and sessilin against Pythium

Cyclic lipopeptides (CLiPs) are secondary metabolites produced by a variety of bacteria. These compounds show a broad range of antimicrobial activities; therefore, they are studied for their potential applications in agriculture and medicine. It is generally assumed that the primary target of the CLiPs is the cellular membrane, where they can permeabilize the lipid bilayer. Model membrane systems are commonly used to investigate the effect of lipid composition on the permeabilizing activity of CLiPs, but these systems do not represent the full complexity of true biological membranes. Here, we introduce a novel method that uses sterol-auxotrophic oomycetes to investigate how the activity of membrane-active compounds is influenced by alterations in membrane sterol composition. More specifically, we investigated how ergosterol, cholesterol, beta-sitosterol and stigmasterol affect the activity of the structurally related Pseudomonas-derived CLiPs tolaasin and sessilin against the oomycete Pythium myriotylum. Both compounds were effective against oomycetes, although tolaasin was considerably more active. Interestingly, tolaasin and sessilin effects were similarly reduced by the presence of sterols, with cholesterol showing the highest reduction of activity.

Insights into the Host Specificity of a New Oomycete Root Pathogen, Pythium brassicum P1: Whole Genome Sequencing and Comparative Analysis Reveals Contracted Regulation of Metabolism, Protein Families, and Distinct Pathogenicity Repertoire

Pythium brassicum P1 Stanghellini, Mohammadi, Förster, and Adaskaveg is an oomycete root pathogen that has recently been characterized. It only attacks plant species belonging to Brassicaceae family, causing root necrosis, stunting, and yield loss. Since P. brassicum P1 is limited in its host range, this prompted us to sequence its whole genome and compare it to those of broad host range Pythium spp. such as P. aphanidermatum and P. ultimum var. ultimum. A genomic DNA library was constructed with a total of 374 million reads. The sequencing data were assembled using SOAPdenovo2, yielding a total genome size of 50.3 Mb contained in 5434 scaffolds, N50 of 30.2 Kb, 61.2% G+C content, and 13,232 putative protein-coding genes. Pythium brassicum P1 had 175 species-specific gene families, which is slightly below the normal average. Like P. ultimum, P. brassicum P1 genome did not encode any classical RxLR effectors or cutinases, suggesting a significant difference in virulence mechanisms compared to other oomycetes. Pythium brassicum P1 had a much smaller proportions of the YxSL sequence motif in both secreted and non-secreted proteins, relative to other Pythium species. Similarly, P. brassicum P1 had the fewest Crinkler (CRN) effectors of all the Pythium species. There were 633 proteins predicted to be secreted in the P. brassicum P1 genome, which is, again, slightly below average among Pythium genomes. Pythium brassicum P1 had only one cadherin gene with calcium ion-binding LDRE and DxND motifs, compared to Pythium ultimum having four copies. Pythium brassicum P1 had a reduced number of proteins falling under carbohydrate binding module and hydrolytic enzymes. Pythium brassicum P1 had a reduced complement of cellulase and pectinase genes in contrast to P. ultimum and was deficient in xylan degrading enzymes. The contraction in ABC transporter families in P. brassicum P1 is suggested to be the result of a lack of diversity in nutrient uptake and therefore host range.

Genome-wide sequencing and metabolic annotation of Pythium irregulare CBS 494.86: understanding Eicosapentaenoic acid production

BACKGROUND

Pythium irregulare is an oleaginous Oomycete able to accumulate large amounts of lipids, including Eicosapentaenoic acid (EPA). EPA is an important and expensive dietary supplement with a promising and very competitive market, which is dependent on fish-oil extraction. This has prompted several research groups to study biotechnological routes to obtain specific fatty acids rather than a mixture of various lipids. Moreover, microorganisms can use low cost carbon sources for lipid production, thus reducing production costs. Previous studies have highlighted the production of EPA by P. irregulare, exploiting diverse low cost carbon sources that are produced in large amounts, such as vinasse, glycerol, and food wastewater. However, there is still a lack of knowledge about its biosynthetic pathways, because no functional annotation of any Pythium sp. exists yet. The goal of this work was to identify key genes and pathways related to EPA biosynthesis, in P. irregulare CBS 494.86, by sequencing and performing an unprecedented annotation of its genome, considering the possibility of using wastewater as a carbon source.

RESULTS

Genome sequencing provided 17,727 candidate genes, with 3809 of them associated with enzyme code and 945 with membrane transporter proteins. The functional annotation was compared with curated information of oleaginous organisms, understanding amino acids and fatty acids production, and consumption of carbon and nitrogen sources, present in the wastewater. The main features include the presence of genes related to the consumption of several sugars and candidate genes of unsaturated fatty acids production.

CONCLUSIONS

The whole metabolic genome presented, which is an unprecedented reconstruction of P. irregulare CBS 494.86, shows its potential to produce value-added products, in special EPA, for food and pharmaceutical industries, moreover it infers metabolic capabilities of the microorganism by incorporating information obtained from literature and genomic data, supplying information of great importance to future work.

[Toxicity of Pythium oligandrum broth to animal and its control effect on rot diseases caused by Penicillium italicum and Penicillium digitatum in orange fruit storage]

OBJECTIVE

In order to develop a safe, nontoxic and efficient biological antistaling agent and to decrease the incidence of rot diseases caused by the Penicillium italicum and Penicillium digitatum in orange fruit storage.

METHODS

the present experiment was carried out with Pythium oligandrum broth (POB) produced by our self-isolated strain (P. oligandrum CQ2010) to study the toxicity to animal. Thereafter, mycelium growth and spore germination of both P. digitatum and P. italicum and control effect of rot disease in orange storage were compared after treated by liquid culture medium (control), POB, prochloraz (PC) , and PC + POB.

RESULTS

Gastric lavage with large amount POB did not influence mouse weight. The animals also showed no abnormality in appearance, behaviors and pathology changes in heart, liver, kidney, lung and intestine. POB decreased the hyphal growth by 70.24% - 93.74% and spore germination by 44.91% - 87.82% (24 h after POB addition) of these two pathogenic fungi. Disease incidence of orange fruit following P. italicum inoculation changed in the sequence: CK > POB > PC > PC + POB and the control efficacy behaved otherwise. In commercial simulation storage, the disease incidence of orange fruit caused by P. digitatum and P. italicum was above 50% of the total. The fruit rot rate was 26.40% (CK), 15.03% (POB), 16.61% (PC) and 4.21% (PC + POB). There were no significant differences in fruit quality under different treatments.

CONCLUSION

POB was safe to animal and could decrease rot disease incidence caused by P. italicum and P. digitatum in orange storage whereby producing a positive interaction with prochloraz and controlling rot diseases caused by these two fungi.

The Immunoreactive Exo-1,3-β-Glucanase from the Pathogenic Oomycete Pythium insidiosum Is Temperature Regulated and Exhibits Glycoside Hydrolase Activity

The oomycete organism, Pythium insidiosum, is the etiologic agent of the life-threatening infectious disease called "pythiosis". Diagnosis and treatment of pythiosis is difficult and challenging. Novel methods for early diagnosis and effective treatment are urgently needed. Recently, we reported a 74-kDa immunodominant protein of P. insidiosum, which could be a diagnostic target, vaccine candidate, and virulence factor. The protein was identified as a putative exo-1,3-ß-glucanase (Exo1). This study reports on genetic, immunological, and biochemical characteristics of Exo1. The full-length exo1 coding sequence (2,229 bases) was cloned. Phylogenetic analysis showed that exo1 is grouped with glucanase-encoding genes of other oomycetes, and is far different from glucanase-encoding genes of fungi. exo1 was up-regulated upon exposure to body temperature, and its gene product is predicted to contain BglC and X8 domains, which are involved in carbohydrate transport, binding, and metabolism. Based on its sequence, Exo1 belongs to the Glycoside Hydrolase family 5 (GH5). Exo1, expressed in E. coli, exhibited ß-glucanase and cellulase activities. Exo1 is a major intracellular immunoreactive protein that can trigger host immune responses during infection. Since GH5 enzyme-encoding genes are not present in human genomes, Exo1 could be a useful target for drug and vaccine development against this pathogen.

Pesticidal activity of metal oxide nanoparticles on plant pathogenic isolates of Pythium

CuO and ZnO nanoparticles (NPs) have antimicrobial effects that could lead to formulations as pesticides for agriculture or medicine. The responses of two soil-borne plant pathogenic Pythium isolates to the NPs were studied to determine the potential of these metal oxide NPs as pesticides. Growth of the P. ultimum isolate was more sensitive to CuO NPs than the P. aphanidermatum isolate. Growth in liquid medium with CuO NPs eliminated culturability whereas exposure to ZnO NPs resulted in stasis with growth resuming on transfer to medium lacking NPs. The citrate in the medium used for the growth assays was involved in enhanced release of the toxic metals from the NPs. Both CuO and ZnO NPs affected processes involved in Fe uptake. The NPs reduced levels of Fe-chelating siderophore-like metabolites produced by Pythium hyphae. CuO NPs inhibited, but ZnO NPs increased, ferric reductase activity detected at the mycelial surface. These findings illustrate that the toxicity of the metal oxide NPs towards Pythium was influenced by the medium, especially by the presence of a metal chelator. Environmental factors are likely to alter the pesticide potential of the metal oxide NPs when formulated for agricultural use in soils.

Detection of the oomycete Pythium insidiosum by real-time PCR targeting the gene coding for exo-1,3-β-glucanase

Pythiosis is a life-threatening infectious disease caused by Pythium insidiosum. Early and accurate diagnosis is the key to prompt treatment and an improved prognosis for patients with pythiosis. An alternative to microbiological and immunological approaches for facilitating diagnosis of pythiosis is the PCR-based assay. Until recently, the ribosomal DNA (rDNA) region was the only target available for PCR-based detection of P. insidiosum. Failure to detect P. insidiosum by PCR amplification using the rDNA-specific primers has been reported. PinsEXO1, encoding an exo-1,3-β-glucanase, is an alternative, novel and efficient target for identification of P. insidiosum by conventional PCR. In this study, we aimed to develop a real-time (RT)-PCR approach targeting PinsEXO1 and compare its performance with conventional PCR for the detection of P. insidiosum. Both conventional and RT-PCR assays were positive for all 35 P. insidiosum strains tested, whilst all 58 control fungi were negative. The turnaround time for conventional PCR was 10 h, whilst that for RT-PCR was 7.5 h. The lowest amounts of genomic DNA template required for successful amplification by conventional and RT-PCR were 1 and 1 × 10(-4) ng, respectively. In conclusion, the RT-PCR assay retained 100% sensitivity and 100% specificity for detection of P. insidiosum. It showed a substantially improved analytical sensitivity and turnaround time that could improve diagnosis of pythiosis. The assay could also facilitate quantitative DNA analysis and epidemiological studies of P. insidiosum.

The safety assessment of Pythium irregulare as a producer of biomass and eicosapentaenoic acid for use in dietary supplements and food ingredients

Polyunsaturated fatty acids, docosahexaenoic acid (DHA, 22:6, n-3), eicosapentaenoic acid (EPA, 20:5, n-3), and arachidonic acid (ARA, 20:4 n-6), have multiple beneficial effects on human health and can be used as an important ingredient in dietary supplements, food, feed and pharmaceuticals. A variety of microorganisms has been used for commercial production of these fatty acids. The microorganisms in the Pythium family, particularly Pythium irregulare, are potential EPA producers. The aim of this work is to provide a safety assessment of P. irregulare so that the EPA derived from this species can be potentially used in various commercial applications. The genus Pythium has been widely recognized as a plant pathogen by infecting roots and colonizing the vascular tissues of various plants such as soybeans, corn and various vegetables. However, the majority of the Pythium species (including P. irregulare) have not been reported to infect mammals including humans. The only species among the Pythium family that infects mammals is P. insidiosum. There also have been no reports showing P. irregulare to contain mycotoxins or cause potentially allergenic responses in humans. Based on the safety assessment, we conclude that P. irregulare can be considered a safe source of biomass and EPA-containing oil for use as ingredients in dietary supplements, food, feed and pharmaceuticals.

Pythium irregulare fermentation to produce arachidonic acid (ARA) and eicosapentaenoic acid (EPA) using soybean processing co-products as substrates

Arachidonic acid (ARA) and eicosapentaenoic acid (EPA) were produced by Pythium irregulare fungus using soybean cotyledon fiber and soy skim, two co-products from soybean aqueous processing, as substrates in different fermentation systems. Parameters such as moisture content, substrate glucose addition, incubation time, and vegetable oil supplementation were found to be important in solid-state fermentation (SSF) of soybean fiber, which is to be used as animal feed with enriched long-chain polyunsaturated fatty acids (PUFA). Soybean fiber with 8 % (dwb) glucose supplementation for a 7-day SSF produced 1.3 mg of ARA and 1.6 mg of EPA in 1 g of dried substrate. When soy skim was used as substrate for submerged fermentation, total ARA yield of 125.7 mg/L and EPA yield of 92.4 mg/L were achieved with the supplementation of 7 % (w/v) soybean oil. This study demonstrates that the values of soybean fiber and soy skim co-products could be enhanced through the long-chain PUFA production by fermentation.

Mycelia promote active transport and spatial dispersion of polycyclic aromatic hydrocarbons

To cope with heterogeneous subsurface environments mycelial microorganisms have developed a unique ramified growth form. By extending hyphae, they can obtain nutrients from remote places and transport them even through air gaps and in small pore spaces, repectively. To date, studies have been focusing on the role that networks play in the distribution of nutrients. Here, we investigated the role of mycelia for the translocation of nonessential substances, using polycyclic aromatic hydrocarbons (PAHs) as model compounds. We show that the hyphae of the mycelial soil oomycete Pythium ultimum function as active translocation vectors for a wide range of PAHs. Visualization by two-photon excitation microscopy (TPEM) demonstrated the uptake and accumulation of phenanthrene (PHE) in lipid vesicles and its active transport by cytoplasmic streaming of the hyphae ('hyphal pipelines'). In mycelial networks, contaminants were translocated over larger distances than by diffusion. Given their transport capacity and ubiquity, hyphae may substantially distribute remote hydrophobic contaminants in soil, thereby improving their bioavailability to bacterial degradation. Hyphal contaminant dispersal may provide an untapped potential for future bioremediation approaches.

Use of dry-milling derived thin stillage for producing eicosapentaenoic acid (EPA) by the fungus Pythium irregulare

This study was to explore the use of thin stillage, a major byproduct in dry milling corn-ethanol plants, for production of eicosapentaenoic acid (EPA) by the fungus Pythium irregulare. Thin stillage contains various compounds that were ideal for fungal growth. Thin stillage concentration and temperature played important roles in fungal growth and EPA production. When 50% thin stillage was used in a stepwise temperature shift culture process, the cell density reached 23 g/L at day 9 with EPA yield and productivity of 243 and 27 mg/L day, respectively. The fungal biomass contained 39% lipid, 28% protein, 30% carbohydrate, and 3% ash. The fungal culture also generated a nutrient-depleted liquid by removing organic compounds in the raw thin stillage. The results collectively showed a new use of thin stillage by feeding to the fungus P. irregulare for producing omega-3 fatty acids.

Nonfeed application of rendered animal proteins for microbial production of eicosapentaenoic acid by the fungus Pythium irregulare

Rendered animal proteins are well suited for animal nutrition applications, but the market is maturing, and there is a need to develop new uses for these products. The objective of this study is to explore the possibility of using animal proteins as a nutrient source for microbial production of omega-3 polyunsaturated fatty acids by the microalga Schizochytrium limacinum and the fungus Pythium irregulare. To be absorbed by the microorganisms, the proteins needed to be hydrolyzed into small peptides and free amino acids. The utility of the protein hydrolysates for microorganisms depended on the hydrolysis method used and the type of microorganism. The enzymatic hydrolysates supported better cell growth performance than the alkali hydrolysates did. P. irregulare displayed better overall growth performance on the experimental hydrolysates compared to S. limacinum. When P. irregulare was grown in medium containing 10 g/L enzymatic hydrolysate derived from meat and bone meal or feather meal, the performance of cell growth, lipid synthesis, and omega-3 fatty acid production was comparable to the that of culture using commercial yeast extract. The fungal biomass derived from the animal proteins had 26-29% lipid, 32-34% protein, 34-39% carbohydrate, and <2% ash content. The results show that it is possible to develop a nonfeed application for rendered animal protein by hydrolysis of the protein and feeding to industrial microorganisms which can produce omega-3 fatty acids for making omega-3-fortified foods or feeds.

Use of biodiesel-derived crude glycerol for producing eicosapentaenoic acid (EPA) by the fungus Pythium irregulare

Crude glycerol is a major byproduct for the biodiesel industry. Producing value-added products through microbial fermentation on crude glycerol provides opportunities to utilize a large quantity of this byproduct. The objective of this study is to explore the potential of using crude glycerol for producing eicosapentaenoic acid (EPA, 20:5 n-3) by the fungus Pythium irregulare . When P. irregulare was grown in medium containing 30 g/L crude glycerol and 10 g/L yeast extract, EPA yield and productivity reached 90 mg/L and 14.9 mg/L x day, respectively. Adding pure vegetable oils (flaxseed oil and soybean oil) to the culture greatly enhanced the biomass and the EPA production. This enhancement was due to the oil absorption by the fungal cells and elongation of shorter chain fatty acids (e.g., linoleic acid and alpha-linolenic acid) into longer chain fatty acid (e.g., EPA). The major impurities contained in crude glycerol, soap and methanol, were inhibitory to fungal growth. Soap can be precipitated from the liquid medium through pH adjustment, whereas methanol can be evaporated from the medium during autoclaving. The glycerol-derived fungal biomass contained about 15% lipid, 36% protein, and 40% carbohydrate, with 9% ash. In addition to EPA, the fungal biomass was also rich in the essential amino acids lysine, arginine, and leucine, relative to many common feedstuffs. Elemental analysis by inductively coupled plasma showed that aluminum, calcium, copper, iron, magnesium, manganese, phosphorus, potassium, silicon, sodium, sulfur, and zinc were present in the biomass, whereas no heavy metals (such as mercury and lead) were detected. The results show that it is feasible to use crude glycerol for producing fungal biomass that can serve as EPA-fortified food or feed.

Inducible expression of a Nep1-like protein serves as a model trigger system of camalexin biosynthesis

Camalexin, the major Arabidopsis phytoalexin, is synthesized in response to a great variety of pathogens. Specific pathogen-associated molecular patterns, such as Nep1-like proteins from oomycetes act as signals triggering the transcriptional activation of the camalexin biosynthetic genes. PaNie, a Nep1-like protein from Pythiumaphanidermatum was expressed in Arabidopsis under the control of an ethanol-inducible promoter. This system was developed as a tool to study the regulation of camalexin biosynthesis. It allowed induction of camalexin preceded by strong transcriptional activation of the tryptophan and camalexin biosynthetic genes. In flowers and green siliques PaNie expression elicited only minor camalexin formation, indicating low capability for phytoalexin synthesis in reproductive organs in contrast to leaf and stem tissue.

Structure of sylvaticin, a new α-elicitin-like protein fromPythium sylvaticum

The structure of sylvaticin, a 10 kDa major pythin protein excreted by the parasitic oomycete Pythium sylvaticum, has been determined. Although closely related to alpha-elicitins in its biological response, toxicity and overall structure, sylvaticin presents a number of structural features that make it an unusual member of the elicitin class. Elicitins possess a large hydrophobic cavity and the mechanism of the systemic acquired resistance induced in planta is known to proceed through lipid transport and complexation within this cavity. Unlike other elicitins, sylvaticin contains tryptophan residues, one of which points inwards towards the central cavity, thus limiting access to sterols. In the case of sylvaticin, the sterol-transport mechanism is likely to be of less importance compared with other members of the elicitin family and still remains to be fully characterized.

In vitro metabolism of ginsenosides by the ginseng root pathogen Pythium irregulare

The role of ginseng saponins (ginsenosides) as modulators or inhibitors of disease is vague, but our earlier work supports the existence of an allelopathic relationship between ginsenosides and soilborne microbes. Interestingly, this allelopathy appears to significantly promote the growth of the important ginseng pathogen, Pythium irregulare while inhibiting that of an antagonistic non-pathogenic fungus, Trichoderma hamatum. Herein we report on the apparent selective metabolism of 20(S)-protopanaxadiol ginsenosides by an extracellular glycosidase from P. irregulare. Thus, when P. irregulare was cultured in the presence of a purified (> 90%) ginsenoside mixture, nearly all of the 20(S)-protopanaxadiol ginsenosides (Rb1, Rb2, Rc, Rd, and to a limited extent G-XVII) were metabolized into the minor ginsenoside F2, at least half of which appears to be internalized by the organism. No metabolism of the 20(S)-protopanaxatriol ginsenosides (Rg1 and Re) was evident. By contrast, none of the ginsenosides added to the culture medium of the non-pathogenic fungus T. hamatum were metabolized. The metabolism of 20(S)-protopanaxadiol ginsenosides by P. irregulare appears to occur through the hydrolysis of terminal monosaccharide units from disaccharides present at C-3 and/or C-20 of ginsenosides Rb1, Rc, Rb2, Rd and G-XVII to yield one major product, ginsenoside F2 and one minor product (possibly G-III). A similar transformation of ginsenosides was observed using a crude protein preparation isolated from the spent medium of P. irregulare cultures.

Molecular cloning of the gene encoding β-1,3(4)-glucanase A from a marine bacterium, Pseudomonas sp. PE2, an essential enzyme for the degradation of Pythium porphyrae cell walls

The beta-1,3(4)-glucanase A (GluA)-encoding gene named gluA was cloned from the genomic library of a marine bacterium Pseudomonas sp. PE2 by expression in Escherichia coli, and the complete DNA sequence was determined. The recombinant enzyme from Pseudomonas sp. PE2 was examined to determine the essential enzymes for degrading Pythium porphyrae cell walls, comparatively using other two recombinant enzymes, chitinase A and beta-1,3-glucanase B from the same bacterial strain. GluA most degraded the cell walls among these three enzymes, suggesting that GluA seems to be most important to P. porphyrae cell-wall-degrading activity. The deduced GluA is a modular enzyme composed of an N-terminal signal peptide, the tandem-duplicated carbohydrate-binding module family 6 (CBM(GluA)-1 and CBM(GluA)-2), and a glycoside hydrolase family 16 catalytic domain. Deletion analysis clearly indicated that GluA lacking CBM(GluA)-1 and CBM(GluA)-2 does not bind to Avicel and xylan. These results suggest that the tandem-repeated CBM of GluA may play a key role in the binding of Avicel and xylan as well as beta-1,3- and beta-1,3;1,4-glucans and is very important to bind to insoluble polysaccharides.

Characterisation of the early events in atypical tomato root colonisation by a biocontrol agent, Pythium oligandrum

The specific oomycete-plant relationship established between a biological agent, Pythium oligandrum, and tomato (Lycopersicon esculentum Mill.) plants was examined over the first 48 h after inoculation of tomato roots with the antagonist. One of the most significant effects was the quick colonisation of cortical and vascular root areas by P. oligandrum (until 9 h post-inoculation); it was similar to invasions by the major pathogens of Pythium genus, and much faster than those by Pythium-minor pathogens. Despite the multiplication of hyphae in the root areas, fungal colonisation was associated with neither host wall disruption nor host cell alterations. The colonising hyphae looked healthy till the ninth hour after inoculation, then, they progressively became highly vacuolated. Cytological observations showed that, over the first 14 h of experiment, oomycete invasion was accompanied with rare host-induced defence reactions. Biochemical analysis evidenced an accumulation of phenolic compounds starting 3 h after inoculation. The 14th hour corresponded to the beginning of rishitin (phytoalexin) synthesis. Accumulation of biochemical host defence compounds was concomitant with early signs of hyphae alterations. During the next 34 h several host reactions were regularly amplified as evidenced by the plugging of invaded host cells with heterogeneous osmiophilic or high electron-dense (ED) materials. Fungal cell decay was accompanied with the formation of oogonia in the cortex, vascular parenchyma and xylem vessels. All these early events suggest a peculiar relationship established between P. oligandrum and the plant.

Effects of the humic substances of de-inking paper sludge on the antagonism between two compost bacteria and Pythium ultimum

We investigated the in vitro influence of humic substances (HS) extracted from de-inking paper sludge compost on the inhibition of Pythium ultimum by two compost bacteria, Rhizobium radiobacter (Agrobacterium radiobacter) and Pseudomonas aeruginosa. When low concentrations (5 or 50 mg l(-1)) of HS were added to the culture medium, fungal inhibition by R. radiobacter significantly increased (P<0.01) by 2-3%. In contrast, these low levels of HS had no effect on P. ultimum inhibition by P. aeruginosa. The Fe, chelated by HS, was in part responsible for the decrease of P. ultimum inhibition by the bacteria when increasing amounts of HS were added in the culture medium. The addition of 500 mg l(-1) of humic acids isolated from de-inking paper sludge compost or from fossil origin completely eliminated the inhibition of P. ultimum by R. radiobacter. This Fe effect also stimulated growth of R. radiobacter and reduced its siderophore production in a minimal medium supplemented with HS as sole source of Fe. The results showed that HS influence microbial antagonism when added to a culture medium. However, this effect varies with different factors such as the type of bacteria, concentration of HS, molecular weight and Fe content.

Purification, crystallization and preliminary X-ray studies of sylvaticin, an elicitin-like protein from Pythium sylvaticum

Sylvaticin belongs to the elicitin family. These 10 kDa oomycetous proteins induce a hypersensitive response in plants, including necrosis and cell death, but subsequently leading to a non-specific systemic acquired resistance (SAR) against other pathogens. Sylvaticin has been crystallized using PEG 2000 MME as a precipitant agent in the presence of nickel chloride. The crystals belong to space group C2, with unit-cell parameters a = 99.29, b = 25.67, c = 67.45 A, beta = 99.66 degrees. Diffraction data were recorded to 2.1 A resolution at a synchrotron-radiation source.

Transformation of Pythium aphanidermatum to geneticin resistance

Conditions for the production of protoplasts and gene transfer in Pythium aphanidermatum were investigated. Efficient protoplast generation was possible after culture of mycelium in potato dextrose broth followed by digestion with 0.5% (w/v) each of cellulase and beta- d-glucanase. Plasmid pHAMT35N/SK encoding the nptII gene under control of the Ham34 promoter from the oomycete Bremia lactucae was used to define electroporation parameters for gene transfer. A square-wave electroporation pulse of 2500 V/cm at 50 microF capacitance reproducibly produced transformants, albeit at low efficiency (0.1-0.4 transformants from approximately 10(5) regenerable protoplasts per microgram of DNA). Thirty-two independent transformants exhibited wild-type growth on potato dextrose agar amended with geneticin at 50 microg/ml, a concentration that near completely inhibited the growth of untransformed P. aphanidermatum. Southern blot analysis indicated that transforming DNA was integrated into the oomycete genome and that the DNA was stably inherited through sporogenesis. Growth on geneticin-free media, the ability to form zoospores or oospores, and the ability to cause disease in sugarbeet seedlings in the laboratory were indistinguishable between a subset of the transformed isolates and the progenitor isolate 898B. Co-electroporation of pHAMT35N/SK with plasmid pACT-GUS encoding the Escherichia coli gusA gene controlled by oomycete transcriptional promoter and terminator sequences or with pEGFP encoding enhanced green fluorescent protein under the control of the immediate early promoter from the mammalian cytomegalovirus produced, respectively, stable beta-glucuronidase and transient expression of blue-green fluorescence. Application of the technique to studies on the biochemical basis for pathogenesis in this agriculturally important group of fungi is discussed.

Comparative degradation of oomycete, ascomycete, and basidiomycete cell walls by mycoparasitic and biocontrol fungi

Fourteen fungi (primarily representing mycoparasitic and biocontrol fungi) were tested for their ability to grow on and degrade cell walls (CWs) of an oomycete (Pythium ultimum), ascomycete (Fusarium equisetii), and basidiomycete (Rhizoctonia solani), and their hydrolytic enzymes were characterized. Protein was detected in the cultural medium of eleven of the test isolates, and these fungi significantly degraded CWs over the 14-day duration of the experiment. In general, a greater level of CW degradation occurred for F. equisetii and P. ultimum than for R. solani. Fungi that degraded F. equisetii CWs were Coniothyrium minitans, Gliocladium roseum, Myrothecium verrucaria, Talaromyces flavus, and Trichoderma harzianum. Taxa degrading P ultimum CWs included Chaetomium globosum, Coniothyrium minitans, M. verrucaria, Seimatosporium sp., Talaromyces flavus, Trichoderma hamatum, Trichoderma harzianum, and Trichoderma viride. Production of extracellular protein was highly correlated with CW degradation. Considerable variation in the molecular weights of CW-degrading enzymes were detected among the test fungi and the CW substrates in zymogram electrophoresis. Multivariate analysis between CW degradation and hydrolysis of barley beta-glucan (beta1,3- and beta1,4-glucanases), laminarin (beta1,3- and beta1,6-glucanases), carboxymethyl cellulose (endo-beta1,4-glucanases), colloidal chitin (chitinases), and chitosan (chitosanases) was conducted. For F. equisetii CWs, the regression model accounted for 80% of the variability, and carboxymethyl cellulases acting together with beta-glucanases contributed an R2 of 0.52, whereas chitinases and beta-glucanases alone contributed an R2 of 0.11 and 0.12, respectively. Only 61% of the variability observed in the degradation of P. ultimum CWs was explained by the enzyme classes tested, and primarily beta-glucanases (R2 of 0.53) and carboxymethyl cellulases (R2 of 0.08) alone contributed to CW break down. Too few of the test fungi degraded R. solani CWs to perform multivariate analysis effectively. This study identified several fungi that degraded ascomyceteous and oomyceteous, and to a lesser extent, basidiomycetous CWs. An array of enzymes were implicated in CW degradation.

A new species of Pythium with filamentous sporangia having pectinolytic activities, isolated in the Burgundy region of France

A new species, Pythium pectinolyticum (F-83.1), isolated from soil samples taken in the Burgundy region is being described here. This species is characterised by its filamentous non-inflated type of sporangia, smooth-walled mostly catenulate oogonia and very rare antheridia. This fungus is a very slow-growing organism on most of the solid media, but it grows well in liquid media and also on those containing pectin as the sole source of carbon. Morphological features are described here together with the sequences of the internal transcribed spacer 1 region of the nuclear ribosomal DNA of the fungus, its comparison with related species, and its pectinolytic behaviour.

[Effect of vitamin E and its functional analogs with different molecular structures on growth and lipids content of Pythium debaryanum]

The effect of exogenously added vitamin E and its synthetic analogues (the hydrophilic form of vitamin E and chromans C13 and C1) on the growth, lipogenic activity, and the fatty acid composition of the eicosapolyenoic acid-synthesizing oomycete Pythium debaryanum was studied. The effect was found to depend on the molecular structure of particular compounds. For instance, vitamin E and chroman C13 stimulated fungal growth, whereas chroman C1 inhibited it. The hydrophilic form of vitamin E enhanced the lipogenic activity of the oomycete. The studied compounds, which possess antioxidant activity, did not exert any noticeable effect on the level and the degree of the unsaturation of fungal lipids.

[Effect of exogenous sterols on the growth and fatty acid composition of the oomycete Pythium debaryanum]

Exogenous ergosterol and cholesterol were found to affect the growth and lipogenesis of the oomycete fungus Pythium debaryanum, which is unable to synthesize de novo steroid compounds. These sterols stimulated the growth of the fungus during its submerged cultivation in glucose-peptone medium. This was accompanied by the shortening of the lag phase, the lengthening of the period of active growth, and by a 3.7- or 4.3-fold increase in the maximum biomass in response to the addition of ergosterol or cholesterol, respectively. In the presence of ergosterol, the cellular content of polyenoic fatty acids increased, and the relative content of eicosapolyenoic fatty acids reached 31.4% of the total amount of fatty acids in cells. Conversely, cholesterol decreased the cellular content of polyenoic acids, and the relative content of eicosapolyenoic acids fell to 19.6% of the total amount of fatty acids. It may be inferred that exogenous sterols enhance the yield of pharmacologically active polyenoic acids because of the growth stimulation.

Immuno-capture differential display method (IDDM) for the detection of environmentally induced promoters in rhizobacteria

A rapid immunological method for trapping and selection of functionally regulated prokaryotic promoters is described. The method is based on application of a novel mini-Tn5 derived promoter probe (pUTTKZY-promoterless lacZY as a reporter and kanamycin resistance) to mutagenise a plant growth promoting fluorescent pseudomonad, Pseudomonas fluorescens 54/96. The transposon allows selection of operon fusion mutants (lacZY(+)) directly on media containing lactose as a sole carbon source as well as selection for kanamycin and lacZ (beta-galactosidase) expression on X-gal indicator media. We have extended the technique to target the surface expression of the induced lactose permease gene (lacY) from mutagenised libraries and the immuno-capture of bacteria with magnetic beads and anti-LacY monospecifc antisera. The benefits of the lacZY reporter are that a library can be rapidly generated and screened in vitro to isolate non-expressed mutants for further in situ screening. Here we demonstrate the development and utility of the technique and its potential as a differential display method for the isolation of promoters that direct regulated gene expression in the phytosphere, or under other imposed conditions.

Phytotoxicity of indole-3-acetic acid produced by the fungus, Pythium aphanidermatum

Pythium aphanidermatum causes the serious disease of Pythium red blight on bentgrass. IAA, one of the metabolites that has been isolated from this fungus, showed the same symptom of Pythium red blight on bentgrass at a concentration of 1,000 mg/1. The IAA content in the foliage of bentgrass infected by this fungus was about 200 times that of an untreated control. These results suggest that IAA produced by this fungus was the causal substance of Pythium red blight on bentgrass.

Analysis of beta-tubulin cDNAs from taxol-resistant Pestalotiopsis microspora and taxol-sensitive Pythium ultimum and comparison of the taxol-binding properties of their products

The anti-cancer drug taxol binds to beta-tubulin in assembled microtubules and causes cell cycle arrest in animal cells; in contrast, in fungi, the effect of taxol varies. For instance, the taxol-producer Pestalotiopsis microspora Ne32, an ascomycete, is resistant to taxol (IC50 greater than 11.7 microM), whereas Pythium ultimum, an oomycete, is sensitive to taxol (IC50 0.1 microM). In order to understand the differential fungal response to taxol, we isolated cDNAs encoding beta-tubulin from both P. microspora and P. ultimum. The deduced amino acid sequence of beta-tubulin from P. microspora is very similar to those from other Ascomycetes, many of which are resistant to taxol. The sequence of beta-tubulin from P. ultimum is very similar to those from Oomycetes and non-fungal organisms, many of which are sensitive to taxol. To examine the interaction between taxol and fungal microtubules, binding studies were performed with fungal cells, using [3H]taxol. The labeled taxol was found to bind specifically to P. ultimum, but not to P. microspora. In addition, the amount of [3H]taxol specifically bound to P. ultimum was reduced by the microtubule-depolymerizing drug thiabendazole, in a dose-dependent manner. These results suggest efficient binding of taxol to microtubules in P. ultimum, but not in P. microspora, and are consistent with the differential taxol sensitivity of these two organisms. Finally a comparison of previously characterized taxol binding sites in various beta-tubulin sequences showed that beta-tubulins of taxol-sensitive organisms, including P. ultimum, contain Thr219, but beta-tubulins of resistant organisms, including P. microspora, contain Asn or Gln at this position, suggesting an important role for residue 219 in the interaction between taxol and beta-tubulin.

Regulation of enzymes involved in anthocyanin biosynthesis in carrot cell cultures in response to treatment with ultraviolet light and fungal elicitors

The accumulation of anthocyanins in cell cultures of Daucus carota L. and the enzymes involved in their biosynthesis were investigated under growth in the dark, continuous irradiation with UV light, incubation with elicitors from Pythium aphanidermatum, and elicitor treatment of UV-irradiated cells. Upon UV irradiation, anthocyanin accumulation was strongly enhanced, and the enzymes of the phenylpropanoid and flavonoid pathways, including the "late" enzymes cyanidin galactosyltransferase, cyanidin galactoside xylosyltransferase, cyanidin triglycoside sinapoyltransferase and sinapic acid glucosyltransferase, all showed transient increases in their activities. The time courses of the enzyme activities exhibited successive maxima with an ordered sequence corresponding to their position in the biosynthetic pathway, suggesting a coordinated induction of the entire set of enzymes. The key enzymes phenylalanine ammonia-lyase and chalcone synthase are regulated on a transcriptional level. Incubation of dark-grown carrot cells with fungal elicitors led to a rapid and transient induction of phenylalanine ammonia-lyase corresponding to the formation of 4-hydroxybenzoic acid, but the amount of anthocyanin did not increase and there was no enhancement of any of the enzyme activities which are part of the anthocyanin pathway, including the enzymes catalyzing glycosylation and acylation reactions. Treatment with UV light and elicitors resulted in a rapid induction of the phenylpropanoid pathway, whereas the inducing effect of UV light on the anthocyanin content, on chalcone synthase and on the enzymes catalyzing the final steps of anthocyanin biosynthesis was suppressed. These results indicate a coordinated regulation of the enzymes involved in anthocyanin biosynthesis, an independent inducibility of the phenylpropanoid pathway, and a hierarchy of the different effectors, as shown by the dominating role of the elicitor-signal over the UV stimulus.

Crystal structure of a fungal elicitor secreted by Phytophthora cryptogea, a member of a novel class of plant necrotic proteins

BACKGROUND

Elicitins form a novel class of plant necrotic proteins which are secreted by Phytophthora and Pythium fungi, parasites of many economically important crops. These proteins induce leaf necrosis in infected plants and elicit an incompatible hypersensitive-like reaction, leading to the development of a systemic acquired resistance against a range of fungal and bacterial plant pathogens. No crystal structures of this class of protein are available. The crystal structure determination of beta-cryptogein (CRY), secreted by Phytophthora cryptogea, was undertaken to identify structural features important for the necrotic activity of elicitins.

RESULTS

The structure of CRY was determined using the multiwavelength anomalous diffraction technique and refined to 2.2 A resolution. The overall structure has a novel fold consisting of six alpha helices and a beak-like motif, whose sequence is highly conserved within the family, composed of an antiparallel two-stranded beta sheet and an omega loop. This motif is assumed to be a major recognition site for a putative receptor and/or ligand. Two other distinct binding sites seem to be correlated to the level of necrotic activity of elicitins.

CONCLUSIONS

The determination of the crystal structure of a member of the elicitin family may make it possible to separate the activity that causes leaf necrosis from that inducing systemic acquired resistance to pathogens, making it feasible to engineer a non-toxic elicitin that only elicits plant defences. Such studies should aid the development of non-toxic agricultural pest control.

Effect of cultural conditions on production of eicosapentaenoic acid by Pythium irregulare

The effect of culture conditions upon lipid content and fatty acid composition of mycelia of Pythium irregulare was investigated with particular attention to increasing the yield of 5,8,11,14,17-eicosapentaenoic acid (20:5; omega-3)(EPA). All experiments were done by shake flask culture using a yeast extract + malt extract medium. The maximum growth rate was obtained at 25 degrees C, but maximum EPA production was obtained at 12 degrees C. The highest EPA production was 76.5 micrograms EPA/ml 13 days fermentation at 12 degrees C. Addition of glucose during fermentation increased the yield considerably. The highest yield was 112 micrograms/ml, obtained at 13 days fermentation with spiking on day 11. Fermentation time could be shortened by initial incubation at 25 degrees C for 2 days, followed by incubation at 12 degrees C for 6 days. The culture also produced arachidonic acid and other omega-6 polyunsaturated fatty acids. EPA production was also obtained with lactose or sweet whey permeate, a by-product of cheese manufacture that contains lactose as the main carbohydrate.

Production of the polyunsaturated fatty acids arachidonic acid and eicosapentaenoic acid by the fungus Pythium ultimum

Several strains of species of the fungal genus Pythium, and of Phytophthora cinnamomi, were screened for content of the polyunsaturated fatty acids (PUFAs) arachidonic acid (AA) and eicosapentaenoic acid (EPA). The aim of the investigation was to establish alternative sources of these PUFAs, which are of importance in human nutrition. As a relatively prolific producer of EPA and AA, P. ultimum strain #144 was selected for a study of conditions that enhance their production over baseline levels that are present in the fungus when cultured for 6 d at 25 degrees C with rotary shaking (120 r.p.m.) in Vogel's medium containing sucrose as the carbon substrate. The levels of AA and EPA under these conditions were 133 +/- 27 and 138 +/- 25 mg l-1 (n = 5), respectively. Maximal production of these fatty acids was accomplished by the following sequence of steps. (1) Incubate the cultures for 6 d after inoculation under the conditions described above. Then (2) add glucose to the cultures (2%, w/v, final concentration) and incubate for a further 6 d at 13 degrees C. Under these conditions, the AA content of the mycelium was 205% higher than baseline levels and the EPA content was 198% higher. (3) Allow the cultures to remain stationary for 10 d which increases the AA content to 253% above baseline levels and the EPA content by 236%. Using such a procedure, 322 mg AA l-1 and 383 mg EPA 1-1 were produced.

Fungitoxicity of m-fluorophenylalanine-containing peptides towards Pythium ultimum

The tripeptide L-m-fluorophenylalanyl-L-alanyl-L-alanine was much more fungitoxic towards Pythium ultimum than the dipeptide L-m-fluorophenylalanyl-L-alanine or m-fluorophenylalanine. The fungitoxicity of the tripeptide was reduced by L-alanyl peptides and phenylalanine, but not by other amino acids. In contrast, the fungitoxicity of m-fluorophenylalanine was unaffected by peptides, and was antagonized by several amino acids. These results suggest the effective delivery of m-fluorophenylalanine into the cell by a tripeptide carrier.

Changes in the chemical composition of oospores of Pythium aphanidermatum during bimodal germination

The developmental mode by which oospores of Pythium aphanidermatum germinate may be controlled by the concentration of glucose present in the germination medium. When incubated in a liquid medium containing emulsified lecithin without added glucose (S + L), oospores germinated indirectly, with zoospore release occurring during the 10th to 13th h. A decrease in dry weight of the fungus took place by the 13th h of indirect germination. When 0.2 mM glucose was added to S + L, the dry weight of germlings increased and direct germination occurred without zoospore formation. Polar lipid comprised the bulk of total acylglycerides of dormant oospores. A greater decrease in total fatty acid content took place during direct germination than during indirect germination. During both developmental modes of germination, polar lipid content decreased considerably; neutral lipids, however, increased during indirect germination and decreased during direct germination. Protein content of the fungus increased in both developmental modes of germination, being initially 9.7% of the dry weight of dormant oospores. After 13 h of incubation, KOH-soluble polysaccharide decreased by 35% during direct germination and by 48% during indirect germination.

Carbon and nitrogen nutrition of plant pathogenic fungi associated with basal stem rots of cowpeas, Vigna unguiculata (L) Walp in Nigeria

Pythium aphanidermatum, Rhizoctonia bataticola (syn. = Macrophomina phaseolina), Botryodiplodia theobromae, and two strains of Sclerotium rolfsii readily utilized for growth the monosaccharides glucose, fructose and mannose, the disaccharides sucrose and maltose and the polysaccharides dextrin and starch. In addition, S. rolfsii grew appreciably well on carboxymethylcellulose (CMC). When filter paper (nature cellulose) was supplied as sole carbon source, it was decomposed by B. theobromae, S. rolfsii (SR2) and R. bataticola. In studies on nitrogen utilization, B. theobromae grew best on glutamic acid, P. aphanidermatum on glycine and the two strains of S. rolfsii on ammonium nitrate. R. bataticola utilized casein hydrolysate most effectively for growth. EDTANa2 was a poor nitrogen source for all the pathogens.

Cellulolytic activity of some Pythium species

The cellulolytic activity of Pythium ultimum and P. oligandrum was investigated in vitro during the mycelium growth. It was found that under a constant temperature of 24 degrees C the cellulolytic activity was changed according to the pH of the medium. The optimum of cellulolytic activity in P. ultimum was recorded at neutral pH, whereas that in P. oligandrum in acid medium. The enzymatic production depended on the age of culture as well.

Effect of coumarin on growth and metabolism of Pythium

Coumarin concentrations that inhibited growth of Pythium sp. rapidly decreased the rate of incorporation of [14C]glucose into the mycelium. Coumarin also reduced drastically the carbohydrate and protein content of the cytoplasm and, to a lesser extent, the amino acid content and cell wall fraction. Enzymes related to the metabolism of cell wall polysaccharides were not affected during early exposure to the inhibitor. The possible mechanism of coumarin action via inhibition of glucose uptake is discussed in the light of the present findings.

Cholesterol beta-D-glucoside-6'-O-palmitate, a metabolite of Pythium sylvaticum

Cholesterol beta-D-glucoside-6'-O-palmitate has been identified as a polar metabolite in the mycelium of mated cultures of Pythium sylvaticum grown in the presence of cholesterol. The structure was confirmed by synthesis of the metabolite. Similar steroid beta-D-glucoside-6'-O-palmitates were obtained from beta-sitosterol and campesterol when these sterols were added to cultures of P-sylvaticum. Corresponding esters of myristic and stearic acids were also detected.

Differential uptake and metabolism of sitosterol and cholesterol by Achlya, Pythium, and Phytophthora species

The relative ability of isolates of Achlya bisexualis and A. ambisexualis and isolates of Pythium and Phytophthora to take up and metabolize sitosterol and cholesterol was studied. Species of Pythium and Phytophthora took up cholesterol and sitosterol efficiently, whereas Achlya species took up booth sterols inefficiently. Species of Pythium and Phytophthora produced a polar metabolite and esters from sitosterol as they did from cholesterol. Achlya species did not produce the polar metabolite from either sterol. In these experiments Achlya species produced esters only from cholesterol; however, their failure to produce esters from sitosterol may have been due to the higher sitosterol than cholesterol concentration.