Sterol ester hydrolase in Fusarium oxysporum

Comparison of Fusarium graminearum Transcriptomes on Living or Dead Wheat Differentiates Substrate-Responsive and Defense-Responsive Genes

Fusarium graminearum is an opportunistic pathogen of cereals where it causes severe yield losses and concomitant mycotoxin contamination of the grains. The pathogen has mixed biotrophic and necrotrophic (saprophytic) growth phases during infection and the regulatory networks associated with these phases have so far always been analyzed together. In this study we compared the transcriptomes of fungal cells infecting a living, actively defending plant representing the mixed live style (pathogenic growth on living flowering wheat heads) to the response of the fungus infecting identical, but dead plant tissues (cold-killed flowering wheat heads) representing strictly saprophytic conditions. We found that the living plant actively suppressed fungal growth and promoted much higher toxin production in comparison to the identical plant tissue without metabolism suggesting that molecules signaling secondary metabolite induction are not pre-existing or not stable in the plant in sufficient amounts before infection. Differential gene expression analysis was used to define gene sets responding to the active or the passive plant as main impact factor and driver for gene expression. We correlated our results to the published F. graminearum transcriptomes, proteomes, and secretomes and found that only a limited number of in planta- expressed genes require the living plant for induction but the majority uses simply the plant tissue as signal. Many secondary metabolite (SM) gene clusters show a heterogeneous expression pattern within the cluster indicating that different genetic or epigenetic signals govern the expression of individual genes within a physically linked cluster. Our bioinformatic approach also identified fungal genes which were actively repressed by signals derived from the active plant and may thus represent direct targets of the plant defense against the invading pathogen.

Characterization of Melanocarpus albomyces steryl esterase produced in Trichoderma reesei and modification of fibre products with the enzyme

Melanocarpus albomyces steryl esterase STE1 is considered to be an interesting tool for several industrial applications due to its broad substrate specificity. STE1 was produced in the filamentous fungus Trichoderma reesei in a laboratory bioreactor at an estimated production level of 280 mg l(-l). The properties of the purified recombinant enzyme (rSTE1), such as substrate specificity, molecular mass, pH optimum and stability and thermostability, were characterized and compared to the corresponding properties of the native enzyme. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed one band with a molecular weight of 60 kDa for rSTE1, whereas analytical gel filtration showed a dimeric structure with a molecular weight of 120 kDa. The rSTE1 was somewhat less stable under different conditions and had slightly lower activities on various substrates than the native STE1. The effects of rSTE1 on the properties of paper sheets and polyethylene terephthalate (PET) fabric were preliminarily evaluated. Due to the hydrolysis of triglycerides and steryl esters by the rSTE1 treatment, the tensile strength and hydrophilicity of the paper were increased. The rSTE1 treatment increased significantly the polarity of PET by hydrolysing the ester bonds in the polyester backbone. Dyeing of PET with methylene blue was also slightly improved after rSTE1 treatment.

Novel cholesterol esterase secreted by Streptomyces persists during aqueous long-term storage

We isolated a moderate thermophilic actinomycete, Streptomyces sp. X9, from soil and purified cholesterol esterase (CHE) from the culture medium to homogeneity. The molecular masses of the purified CHE estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel filtration chromatography were 23.6 and 163 kDa, respectively, indicating that the enzyme assumes an oligomeric form. Heavy metals such as Hg2+ and Ag+ similarly inhibited the activity of the CHE in the same manner as those of other bacterial CHEs. The activity of Streptomyces sp. X9 CHE was susceptible to dithiothreitol, beta-mercaptoethanol and p-chloromercuribenzoate, but resistant to phenylmethylsulfonyl fluoride, unlike those of other bacterial CHEs. The purified CHE could utilize both cholesteryl and p-nitrophenyl (pNP) esters of fatty acids as substrates. Steady-state kinetics revealed respective Km values for cholesteryl myristate and pNP-myristate of 0.34 and 1.1 mM, indicating that the cholesteryl residue is important for catalysis. We also found that the Km for the pNP esters are dependent on the chain length of the substrate fatty acid residues. These results indicate that the novel CHE specifically hydrolyzes substrates by recognizing both cholesteryl and fatty acid moieties. The enzyme was stable during long-term aqueous storage at room temperature, indicating its potential application as a diagnostic reagent.

Characterisation of steryl esterase activities in commercial lipase preparations

Triglycerides, steryl esters, resin acids, free fatty acids and sterols are lipophilic extractives of wood (commonly referred to as pitch or wood resin) and have a negative impact on paper machine runnability and quality of paper. Thus, enzymes capable of modifying these compounds would be potential tools for reducing pitch problems during paper manufacture. In this work, 19 commercial lipase preparations were tested for their ability to degrade steryl esters, which may play a significant role in the formation and stabilisation of pitch particles. Six lipase preparations were shown to be able to degrade steryl esters. Lipase preparations of Pseudomonas sp., Chromobacterium viscosum and Candida rugosa were shown to have the highest steryl esterase activities. The enzymes were able to hydrolyse steryl esters totally in the presence of a surfactant (Thesit). Up to 80% of the steryl esters were degraded in aqueous dispersion. Preliminary characterisation of the enzymatic activities revealed that the lipase preparation of Pseudomonas sp. could be the most potential enzyme in industrial applications. The steryl esterase activity of this preparation was stable over a broad pH range and the enzyme was able to act efficiently at pH 6-10 and at temperatures up to 70 degrees C.

Production, isolation and characterization of a sterol esterase from Ophiostoma piceae

We studied extracellular sterol esterase production by the ascomycete Ophiostoma piceae in liquid culture. Esterase activity was found in low levels in glucose medium but it was strongly induced by olive oil. An esterase was purified from the 0.5% olive oil-supplemented cultures using ultrafiltration followed by a single chromatographic step on a hydrophobic interaction column. The enzyme was a glycoprotein with 8% N-linked carbohydrate content, a molecular mass by SDS/PAGE around 56.5 kDa and an isoelectric point of 3.3. Its N-terminal sequence was TTVNVKYPEGEVV. Substrate specificity studies showed that the O. piceae esterase hydrolyzes p-nitrophenol esters, tributyrin, triolein and different cholesterol esters. Both affinity (Km) and catalytic constant (k(cat)) were positively affected by the length of the fatty acid esterifying glycerol and cholesterol. The presence of double bonds in the acyl chain increased the enzyme efficiency, although it affected the k(cat) values rather than the Km on the cholesterol esters. The O. piceae enzyme showed no interfacial activation. This enzyme could have biotechnological applications in paper manufacturing since it efficiently hydrolyzes both triglycerides and sterol esters, which form pitch deposits during manufacturing of softwood and hardwood paper pulps, respectively.

Antimicrobial effects of clofibrate on the wheat pathogen Fusarium culmorum

The biological effects of clofibrate (ethyl p-chlorophenoxy-isobutyric acid) on the growth and metabolism of the soil-borne wheat pathogen Fusarium culmorum, were examined. In mid log phase (16 hr) cultures both phenylalanine uptake and secondary spore production were stimulated at 0.1 microM concentration; the net sterol content was reduced 50% at 0.35 microM; oxygen uptake was stimulated at 0.1 mM; growth was inhibited 50% at 0.1 mM concentration. Both phenylalanine and oxygen uptake were inhibited at 1.0 mM and pyruvate dehydrogenase activity was reduced 50% at 50 mM concentration of clofibrate. The data indicate that clofibrate affects a number of biological and enzyme systems. The inhibitory effect on the growth of the pathogen suggest a potential use of hypolipidemic agents like clofibrate as an antifungal agent for seed protection.