Cycloheximide in the nanomolar range inhibits seed germination of Orobanche minor.

From the 992 samples of culture extracts of microorganisms isolated from soil in Japan, we found that the extract of Streptomyces sp. no. 226 inhibited Orobanche minor seed germination without significantly affecting the seed germination of Trifolium pratense and the growth of Aspergillus oryzae and Escherichia coli. Using ESI-MS, 1H-NMR, and 13C-NMR, we identified the active compound as cycloheximide. Cycloheximide had half-maximum inhibitory concentrations of 2.6 ng/mL for the inhibition of seed germination of O. minor and 2.5 µg/mL for that of the conidial germination of A. oryzae. Since cycloheximide is known to inhibit translation by interacting with ribosomal protein L28 (RPL28) in yeast, we investigated whether RPL protein of O. minor plays a critical role in the inhibition of O. minor seed germination. Our data suggested that O. minor RPL27A was not sensitive to cycloheximide by comparing it to the strain expressing S. cerevisiae RPL28. These findings suggest the presence of an unidentified mechanism by which cycloheximide hinders O. minor seed germination.

C-terminus of serine–arginine protein kinase-like protein, SrpkF, is involved in conidiophore formation and hyphal growth under salt stress in Aspergillus aculeatus / El extremo C de la proteína similar a la serina-arginina proteína quinasa, SrpkF, participa en la formación de conidióforos y el crecimiento de hifas bajo estrés salino en Aspergillus aculeatus

The serine–arginine protein kinase–like protein, SrpkF, was identified as a regulator for the cellulose-responsive induction of cellulase genes in Aspergillus aculeatus. To analyze various aspects of SrpkF function, we examined the growth of the control strain (MR12); C-terminus deletion mutant, which produced SrpkF1–327 (ΔCsrpkF); whole gene-deletion mutant of srpkF (ΔsrpkF), srpkF overexpressing strain (OEsprkF); and the complemented strain (srpkF+) under various stress conditions. All test strains grew normally on minimal medium under control, high salt (1.5 M KCl), and high osmolality (2.0 M sorbitol and 1.0 M sucrose). However, only ΔCsrpkF showed reduced conidiation on 1.0 M NaCl media. Conidiation of ΔCsrpkF on 1.0 M NaCl media was reduced to 12% compared with that of srpkF+. Further, when OEsprkF and ΔCsrpkF were pre-cultured under salt stress conditions, germination under salt stress conditions was enhanced in both strains. By contrast, deletion of srpkF did not affect hyphal growth and conidiation under the same conditions. We then quantified the transcripts of the regulators involved in the central asexual conidiation pathway in A. aculeatus. The findings revealed that the expression of brlA, abaA, wetA, and vosA was reduced in ΔCsrpkF under salt stress. These data suggest that in A. aculeatus, SrpkF regulates conidiophore development. The C-terminus of SrpkF seems to be important for regulating SrpkF function in response to culture conditions such as salt stress.(AU)

C-terminus of serine-arginine protein kinase-like protein, SrpkF, is involved in conidiophore formation and hyphal growth under salt stress in Aspergillus aculeatus.

The serine-arginine protein kinase-like protein, SrpkF, was identified as a regulator for the cellulose-responsive induction of cellulase genes in Aspergillus aculeatus. To analyze various aspects of SrpkF function, we examined the growth of the control strain (MR12); C-terminus deletion mutant, which produced SrpkF1-327 (ΔCsrpkF); whole gene-deletion mutant of srpkF (ΔsrpkF), srpkF overexpressing strain (OEsprkF); and the complemented strain (srpkF+) under various stress conditions. All test strains grew normally on minimal medium under control, high salt (1.5 M KCl), and high osmolality (2.0 M sorbitol and 1.0 M sucrose). However, only ΔCsrpkF showed reduced conidiation on 1.0 M NaCl media. Conidiation of ΔCsrpkF on 1.0 M NaCl media was reduced to 12% compared with that of srpkF+. Further, when OEsprkF and ΔCsrpkF were pre-cultured under salt stress conditions, germination under salt stress conditions was enhanced in both strains. By contrast, deletion of srpkF did not affect hyphal growth and conidiation under the same conditions. We then quantified the transcripts of the regulators involved in the central asexual conidiation pathway in A. aculeatus. The findings revealed that the expression of brlA, abaA, wetA, and vosA was reduced in ΔCsrpkF under salt stress. These data suggest that in A. aculeatus, SrpkF regulates conidiophore development. The C-terminus of SrpkF seems to be important for regulating SrpkF function in response to culture conditions such as salt stress.

Independent, cooperative regulation of cellulolytic genes by paralogous transcription factors ClbR and ClbR2 in Aspergillus aculeatus.

The cellobiose-responsive regulator ClbR, a Zn(II)2Cys6 binuclear-cluster transcription factor, is a positive regulator of carbohydrate-active enzyme (CAZyme) genes responsive to cellulose in Aspergillus aculeatus. Because Zn(II)2Cys6 transcription factors tend to dimerize with proteins of the same family, we searched for a counterpart of ClbR and identified ClbR2, which is 42% identical to ClbR, as an interacting partner of ClbR by yeast two-hybrid screening. Genetic analyses suggested that ClbR and ClbR2 cooperatively regulate the expression of CAZyme genes in response to cellulose and 1,4-ß-mannobiose in A. aculeatus. CAZyme genes under the control of the transcription factor ManR were regulated by ClbR and ClbR2, whereas those controlled by the transcription factor XlnR were regulated by ClbR, but not ClbR2. These findings suggest that ClbR participates in multiple regulatory pathways in A. aculeatus by altering an interacting factor.

A new function of a putative UDP-glucose 4-epimerase on the expression of glycoside hydrolase genes in Aspergillus aculeatus.

In order to figure out the induction mechanisms of glycoside hydrolase genes in Aspergillus aculeatus, we screened approximately 9,000 transfer DNA (T-DNA)-inserted mutants for positive regulators involved in the induction. Since the mutants possess the orotidine 5'-monophosphate decarboxylase gene as a reporter gene to monitor the cellulose-responsive expression of the cellobiohydrolase I gene (cbhI), candidate strains were isolated by counterselection against 5-fluoroorotic acid (5-FOA). One 5-FOA-resistant mutant harboring the T-DNA at the uge5 locus showed reduced cellulose utilization and cbhI expression. A. aculeatus Uge5 is homologous to Aspergillus fumigatus uge5 (Afu5g10780; E-value, 0.0; identities, 93%), which catalyzes the conversion of uridine diphosphate (UDP)-glucose to UDP-galactopyranose. The uge5 deletion mutant in A. aculeatus (Δuge5) showed reduced conidium formation on minimal media supplemented with galactose, locust bean gum (LBG), and guar gum as a carbon source. ß-1,4-Endoglucanase and ß-1,4-mannanase production in submerged culture containing LBG was reduced to 10% and 6% of the control strain at day 5, respectively, but no difference was observed in cultures containing wheat bran. The expression of major cellulolytic and mannolytic genes in the presence of mannobiose in Δuge5 was reduced to less than 15% of the control strain, while cellobiose-responsive expression was only modestly reduced at early inducing time points. Since all test genes were controlled by a transcription factor ManR, these data demonstrate that Uge5 is involved in inducer-dependent selective expression of genes controlled via ManR. KEY POINTS: • UDP-glucose 4-epimerase (Uge5) regulates expression of glycosyl hydrolase genes. • ManR regulates both cellobiose- and mannobiose-responsive expression. • Uge5 plays a key role in mannobiose-responsive expression.

Improvement of cellulosic biomass-degrading enzyme production by reducing extracellular protease production in Aspergillus aculeatus.

We investigated the effects of deleting major extracellular protease-encoding genes on cellulolytic and xylanolytic enzyme production in Aspergillus aculeatus. We first investigated the effect of prtT deletion, a positive transcription factor for extracellular protease-encoding genes in Aspergillus, on extracellular protease production in A. aculeatus. Genetic analysis indicated that among the major extracellular proteases, pepIIa and pepIIb are controlled by PrtT, but pepI is not. Thus, we generated a mutant with deletion of the two genes prtT and pepI (ΔprtTΔpepI) and one with deletion of the three genes pepI, pepIIa, and pepIIb (ΔpepIΔIIaΔIIb). Extracellular protease activities decreased in both ΔprtTΔpepI and ΔpepIΔIIaΔIIb to 3% of that in the control strain (MR12). Comparative time-course analyses indicated that endoglucanase activity in ΔprtTΔpepI increased to double that in MR12. Xylanase activities increased in both ΔprtTΔpepI and ΔpepIΔIIaΔIIb to fourfold higher than that in MR12 at maximum. ß-Glucosidase activities were increased in ΔprtTΔpepI and ΔpepIΔIIaΔIIb 1.3- and 1.4-fold higher than that in MR12 at maximum, respectively. Residual activities of endoglucanase, xylanase, and ß-glucosidase after 7 days of incubation at 37°C in the culture supernatant were 63%, 36%, and 48% of the original in MR12. Residual endoglucanase activities were more than 80% of the original in ΔprtT, ΔprtTΔpepI, and ΔpepIΔIIaΔIIb. Residual xylanase activities were not improved in all test strains. ß-Glucosidase remained almost 97% of the original in ΔprtTΔpepI. These findings indicated that the reduction of extracellular proteases effectively improved cellulolytic and xylanolytic enzyme production and stability in A. aculeatus.

Serine-arginine protein kinase-like protein, SrpkF, stimulates both cellobiose-responsive and D-xylose-responsive signaling pathways in Aspergillus aculeatus.

Aspergillus aculeatus produces cellulolytic enzymes in the presence of their substrates. We screened a library of 12,000 A. aculeatus T-DNA-inserted mutants to identify a regulatory factor involved in the expression of their enzyme genes in response to inducers. We found one mutant that reduced the expression of FIII-avicelase (chbI) in response to cellulose. T-DNA was inserted into a putative protein kinase gene similar to AN10082 in A. nidulans, serine-arginine protein kinase F, SrpkF. Fold increases in srpkF gene expression in response to various carbon sources were 2.3 (D-xylose), 44 (Avicel®), 59 (Bacto™ Tryptone), and 98 (no carbon) compared with D-glucose. Deletion of srpkF in A. aculeatus resulted in a significant reduction in cellulose-responsive expression of chbI, hydrocellulase (cel7b), and FIb-xylanase (xynIb) genes at an early induction phase. Further, the srpkF-overexpressing strain showed upregulation of the srpkF gene from four- to nine-fold higher than in the control strain. srpkF overexpression upregulated cbhI and cel7b in response to cellobiose and the FI-carboxymethyl cellulase gene (cmc1) and xynIb in response to D-xylose. However, the srpkF deletion did not affect the expression of xynIb in response to D-xylose due to the less expression of srpkF under the D-xylose condition. Our data demonstrate that SrpkF is primarily involved in cellulose-responsive expression, though it has a potential to stimulate gene expression in response to both cellobiose and D-xylose in A. aculeatus.

Biogenic manganese oxides combined with 1-hydroxybenzotriazol and an Mn(II)-oxidizing enzyme from Pleosporales sp. Mn1 oxidize 3,4-dimethoxytoluene to yield 3,4-dimethoxybenzaldehyde.

Using soil samples, we screened for microbes that produce biogenic manganese oxides (BMOs) and isolated Mn(II)-oxidizing fungus, namely Pleosporales sp. Mn1 (Mn1). We purified the Mn(II)-oxidizing enzyme from intracellular extracts of Mn1. The enzyme oxidized Mn(II) most effectively at pH 7.0 and 45 °C. The N-terminal amino acid sequence of the purified enzyme possessed homology with multicopper oxidases in fungi. The properties of the enzyme and the effects of the pH and inhibitors on the Mn(II)-oxidization activity suggested that the enzyme is a member of the multicopper oxidase family. The X-ray diffraction pattern of the BMOs produced by Mn1 showed a strong correlation with that of a typical poorly crystalized vernadite (δ-MnO2). Since BMOs are some of the most reactive materials in the environment, we investigated a potential new application of BMOs as oxidation catalysts. We confirmed that BMOs oxidized aromatic methyl groups when combined with the purified enzyme and a mediator, 1-hydroxybenzotriazole (HBT). BMO oxidation of 3,4-dimethoxytoluene achieved a better yield than that of abiotic MnO2 and white-rot fungus laccase under acidic and neutral pH conditions. Under neutral pH, the BMOs oxidized 3,4-dimethoxytoluene to yield 200-fold more 3,4-dimethoxybenzaldehyde than that of abiotic MnO2. This is the first report to reveal that BMOs combined with a Mn(II)-oxidizing enzyme and mediator can oxidize aromatic hydrocarbons to yield corresponding aldehydes.

A component of the septation initiation network complex, AaSepM, is involved in multiple cellulose-responsive signaling pathways in Aspergillus aculeatus.

Various carbohydrate-active enzymes in Aspergillus are produced in response to physiological inducers, which is regulated at the transcriptional level. To elucidate the induction mechanisms in Aspergillus, we screened for new regulators involved in cellulose-responsive induction from approximately 10,000 Aspergillus aculeatus T-DNA-inserted mutants. We constructed the T-DNA-inserted mutant library using the host strain harboring the orotidine 5'-monophosphate decarboxylase gene (pyrG) under the control of the FIII-avicelase gene (cbhI) promoter. Thus, candidate mutants deficient in cellulose-responsive induction were positively screened via counter selection against 5-fluoroorotic acid (5-FOA). Among less than two hundred 5-FOA-resistant mutants, one mutant that the T-DNA inserted into the AasepM locus reduced the cbhI expression in response to cellulose. Since AaSepM is similar to Schizosaccharomyces pombe Cdc14p (E-value, 2e-20; identities, 33%), which is a component of the septation initiation network (SIN)-complex, we constructed an AasepM deletion mutant (ΔAasepM). We analyzed the expression of cellulase and xylanase genes in response to cellulose, septation, and conidiation in ΔAasepM. The AasepM deletion leads to delayed septation and decreased formation of the conidium chain in A. aculeatus but does not affect hyphal growth on minimal media. We also confirmed AaSepM's involvement in multiple cellulose-responsive signaling pathways of cellulase and xylanase genes under the control of the ManR-dependent, XlnR-dependent, and ManR- and XlnR-independent signaling pathways. KEY POINTS : • A new regulator for cellulolytic gene expression has been identified. • AaSepM is involved in septation and conidiation in A. aculeatus. • AasepM is involved in multiple cellulose-responsive signaling pathways.

Chemical genetic approach using ß-rubromycin reveals that a RIO kinase-like protein is involved in morphological development in Phytophthora infestans.

To characterize the molecular mechanisms underlying life-stage transitions in Phytophthora infestans, we initiated a chemical genetics approach by screening for a stage-specific inhibitor of morphological development from microbial culture extracts prepared mostly from actinomycetes from soil in Japan. Of the more than 700 extracts, one consistently inhibited Ph. infestans cyst germination. Purification and identification of the active compound by ESI-MS, 1H-NMR, and 13C-NMR identified ß-rubromycin as the inhibitor of cyst germination (IC50 = 19.8 µg/L); ß-rubromycin did not inhibit growth on rye media, sporangium formation, zoospore release, cyst formation, or appressorium formation in Ph. infestans. Further analyses revealed that ß-rubromycin inhibited the germination of cysts and oospores in Pythium aphanidermatum. A chemical genetic approach revealed that ß-rubromycin stimulated the expression of RIO kinase-like gene (PITG_04584) by 60-fold in Ph. infestans. Genetic analyses revealed that PITG_04584, which lacks close non-oomycete relatives, was involved in zoosporogenesis, cyst germination, and appressorium formation in Ph. infestans. These data imply that further functional analyses of PITG_04584 may contribute to new methods to suppress diseases caused by oomycetes.

A Unique Combination of Two Different Quorum Sensing Systems in the ß-Rhizobium Cupriavidus taiwanensis.

Cupriavidus taiwanensis LMG19424, a ß-rhizobial symbiont of Mimosa pudica, harbors phc and tqs quorum sensing (QS), which are the homologous cell-cell communication systems previously identified from the plant pathogen Ralstonia solanacearum and the human pathogen Vibrio cholerae, respectively. However, there has been no experimental evidence reported that these QS systems function in C. taiwanensis LMG19424. We identified (R)-methyl 3-hydroxymyristate (3-OH MAME) and (S)-3-hydroxypentadecan-4-one (C15-AHK) as phc and tqs QS signals, respectively, and characterized these QS systems. The expression of the signal synthase gene phcB and tqsA in E. coli BL21(DE3) resulted in the high production of 3-OH MAME and C15-AHK, respectively. Their structures were elucidated by comparison of EI-MS data and GC/chiral LC retention times with synthetic standards. The deletion of phcB reduced cell motility and increased biofilm formation, and the double deletion of phcB/tqsA caused the accumulation of the metal chelator coproporphyrin III in its mutant culture. Although the deletion of phcB and tqsA slightly reduced its ability to nodulate on aseptically grown seedlings of M. pudica, there was no significant difference in nodule formation between LMG19424 and its QS mutants when commercial soils were used. Taken together, this is the first example of the simultaneous production of 3-OH MAME/C15-AHK as QS signals in a bacterial species, and the importance of the phc/tqs QS systems in the saprophytic stage of C. taiwanensis LMG19424 is suggested.

Actinomycins inhibit the production of the siderophore pyoverdines in the plant pathogen Pseudomonas cichorii SPC9018.

Pyoverdines, a group of peptide siderophores produced by Pseudomonas species, function not only in iron acquisition, but also in their virulence in hosts. Thus, chemical inhibition of pyoverdine production may be an effective strategy to control Pseudomonas virulence. In the plant pathogen Pseudomonas cichorii SPC9018 (SPC9018), pyoverdine production is required for virulence on eggplant. We screened microbial culture extracts in a pyoverdine-production inhibition assay of SPC9018 and found Streptomyces sp. RM-32 as a candidate-producer. We isolated two active compounds from RM-32 cultures, and elucidated their structures to be actinomycins X2 and D. Actinomycins X2 and D inhibited pyoverdine production by SPC9018 with IC50 values of 17.6 and 29.6 µM, respectively. Furthermore, pyoverdine production in other Pseudomonas bacteria, such as the mushroom pathogen P. tolaasii, was inhibited by the actinomycins. Therefore, these actinomycins may be useful as chemical tools to examine pyoverdine functions and as seed compounds for anti-Pseudomonas virulence agents.

Engineering of the Trichoderma reesei xylanase3 promoter for efficient enzyme expression.

The GH10 xylanase XYNIII is expressed in the hyper-cellulase-producing mutant PC-3-7, but not in the standard strain QM9414 of Trichoderma reesei. The GH11 xylanase gene xyn1 is induced by cellulosic and xylanosic carbon sources while xyn3 is induced only by cellulosic carbon sources in the PC-3-7 strain. In this study, we constructed a modified xyn3 promoter in which we replaced the cis-acting region of the xyn3 promoter by the cis-acting region of the xyn1 promoter. The resulting xyn3 chimeric promoter exhibited improved inductivity against cellulosic carbon over the wild-type promoter and acquired inductivity against xylanosic carbon. Furthermore, PC-3-7 expressing the heterologous ß-glycosidase gene, Aspergillus aculeatus bgl1, under the control of the xyn3 chimeric promoter, showed enhanced saccharification ability through increased cellobiase activity. We also show that the xyn3 chimeric promoter is also functional in the QM9414 strain. Our results indicate that the xyn3 chimeric promoter is very efficient for enzyme expression.

Dipeptidyl peptidase IV is involved in the cellulose-responsive induction of cellulose biomass-degrading enzyme genes in Aspergillus aculeatus.

We screened for factors involved in the cellulose-responsive induction of cellulose biomass-degrading enzyme genes from approximately 12,000 Aspergillus aculeatus T-DNA insertion mutants harboring a transcriptional fusion between the FIII-avicelase gene (cbhI) promoter and the orotidine 5'-monophosphate decarboxylase gene. Analysis of 5-fluoroorodic acid (5-FOA) sensitivity, cellulose utilization, and cbhI expression of the mutants revealed that a mutant harboring T-DNA at the dipeptidyl peptidase IV (dppIV) locus had acquired 5-FOA resistance and was deficient in cellulose utilization and cbhI expression. The deletion of dppIV resulted in a significant reduction in the cellulose-responsive expression of both cbhI as well as genes controlled by XlnR-independent and XlnR-dependent signaling pathways at an early phase in A. aculeatus. In contrast, the dppIV deletion did not affect the xylose-responsive expression of genes under the control of XlnR. These results demonstrate that DppIV participates in cellulose-responsive induction in A. aculeatus.

Site-saturation mutagenesis for ß-glucosidase 1 from Aspergillus aculeatus to accelerate the saccharification of alkaline-pretreated bagasse.

Aspergillus aculeatus ß-glucosidase 1 (AaBGL1) is one of the best cellobiose hydrolytic enzymes without transglycosylation products, among ß-glucosidase from various origins, for use in cellulosic biomass conversion with Trichoderma cellulases. However, in our previous report, it was demonstrated that AaBGL1 has lower catalytic efficiency toward cellobiose, which is a major end product from cellulosic biomasses by Trichoderma reesei cellulases, than do gentiobiose and laminaribiose. Thus, we expected that there is room to enhance cellobiose hydrolytic activity of AaBGL1 by increasing catalytic efficiency (k cat/K m) up to that of gentiobiose or laminaribiose for accelerating the saccharification of cellulosic biomasses, and we performed site-saturation mutagenesis targeting nine amino acids supposed to constitute subsite +1 of AaBGL1. We successfully isolated a mutant AaBGL1 (Q201E) having 2.7 times higher k cat/K m toward cellobiose than the WT enzyme. Q201E showed higher activity toward cellotriose and cellotetraose but lower activity toward gentiobiose and laminaribiose than WT. Kinetic analysis of various Q201 mutants toward cellobiose, gentiobiose, and laminaribiose revealed that only the Q201E mutation resulted in improved k cat/K m toward cellobiose. We demonstrated that side chain length and the nondissociated form of the carboxyl group at E201 in Q201E were required for enhancing the activity toward cellooligosaccharides through supporting nucleophile attack by D280 via changing catalytic environment by pH profile of kinetic parameters and mutation analyses. Moreover, we also demonstrated that Q201E produced more effective synergy with cellulases and xylanases than WT in the saccharification of alkaline-pretreated bagasse.

Cytotoxicity and colloidal behavior of polystyrene latex nanoparticles toward filamentous fungi in isotonic solutions.

The effects of surface physicochemical properties of functionalized polystyrene latex (PSL) nanoparticles (NPs) and model filamentous fungi Aspergillus oryzae and Aspergillus nidulans cultivated in different environment (aqueous and atmospheric environment) on the colloidal behavior and cytotoxicity were investigated in different isotonic solutions (154 mM NaCl and 292 mM sucrose). When the liquid cultivated fungal cells were exposed to positively charged PSL NPs in 154 mM NaCl solution, the NPs were taken into A. oryzae, but not A. nidulans. Atomic force microscopy revealed that the uptake of NPs was more readily through the cell wall of A. oryzae because of its relatively softer cell wall compared with A. nidulans. In contrast, the positively charged PSL NPs entirely covered the liquid cultivated fungal cell surfaces and induced cell death in 292 mM sucrose solution because of the stronger electrostatic attractive force between the cells and NPs compared with in 154 mM NaCl. When the agar cultivated fungal cells were exposed to the positively charged PSL NPs, both fungal cells did not take the NPs inside the cells. Contact angle measurement revealed that the hydrophobin on the agar cultivated cell surfaces inhibited the uptake of NPs because of its relatively more hydrophobic cell surface compared with the liquid cultivated cells.

A high performance Trichoderma reesei strain that reveals the importance of xylanase III in cellulosic biomass conversion.

The ability of the Trichoderma reesei X3AB1strain enzyme preparations to convert cellulosic biomass into fermentable sugars is enhanced by the replacement of xyn3 by Aspergillus aculeatus ß-glucosidase 1 gene (aabg1), as shown in our previous study. However, subsequent experiments using T. reesei extracts supplemented with the glycoside hydrolase (GH) family 10 xylanase III (XYN III) and GH Family 11 XYN II showed increased conversion of alkaline treated cellulosic biomass, which is rich in xylan, underscoring the importance of XYN III. To attain optimal saccharifying potential in T. reesei, we constructed two new strains, C1AB1 and E1AB1, in which aabg1 was expressed heterologously by means of the cbh1 or egl1 promoters, respectively, so that the endogenous XYN III synthesis remained intact. Due to the presence of wild-type xyn3 in T. reesei E1AB1, enzymes prepared from this strain were 20-30% more effective in the saccharification of alkaline-pretreated rice straw than enzyme extracts from X3AB1, and also outperformed recent commercial cellulase preparations. Our results demonstrate the importance of XYN III in the conversion of alkaline-pretreated cellulosic biomass by T. reesei.

Characterization of Aspergillus aculeatus ß-glucosidase 1 accelerating cellulose hydrolysis with Trichoderma cellulase system.

Aspergillus aculeatus ß-glucosidase 1 (AaBGL1), which promotes cellulose hydrolysis by Trichoderma cellulase system, was characterized and compared some properties to a commercially supplied orthologue in A. niger (AnBGL) to elucidate advantages of recombinant AaBGL1 (rAaBGL1) for synergistic effect on Trichoderma enzymes. Steady-state kinetic studies revealed that rAaBGL1 showed high catalytic efficiency towards ß-linked glucooligosaccharides. Up to a degree of polymerization (DP) 3, rAaBGL1 prefered to hydrolyze ß-1,3 linked glucooligosaccharides, but longer than DP 3, preferred ß-1,4 glucooligosaccharides (up to DP 5). This result suggested that there were different formation for subsites in the catalytic cleft of AaBGL1 between ß-1,3 and ß-1,4 glucooligosaccharides, therefore rAaBGL1 preferred short chain of laminarioligosaccharides and long chain of cellooligosaccharides on hydrolysis. rAaBGL1 was more insensitive to glucose inhibition and more efficient to hydrolyze the one of major transglycosylation product, gentiobiose than AnBGL, resulting that rAaBGL1 completely hydrolyzed 5% cellobiose to glucose faster than AnBGL. These data indicate that AaBGL1 is valuable for the use of cellulosic biomass conversion.

Characterization and gene cloning of a maltotriose-forming exo-amylase from Kitasatospora sp. MK-1785.

A maltotriose-forming amylase (G3Amy) from Kitasatospora sp. MK-1785 was successfully isolated from a soil sample by inhibiting typical extracellular α-amylases using a proteinaceous α-amylase inhibitor. G3Amy was purified from the MK-1785 culture supernatant and characterized. G3Amy produced maltotriose as the principal product from starch and was categorized as an exo-α-amylase. G3Amy could also transfer maltotriose to phenolic and alcoholic compounds. Therefore, G3Amy can be useful for not only maltotriose manufacture but also maltooligosaccharide-glycoside synthesis. Further, the G3Amy gene was cloned and expressed in Escherichia coli cells. Analysis of its deduced amino acid sequence revealed that G3Amy consisted of an N-terminal GH13 catalytic domain and two C-terminal repeat starch-binding domains belonging to CBM20. It is suggested that natural G3Amy was subjected to proteolysis at N-terminal region of the anterior CBM20 in the C-terminal region. As with natural G3Amy, recombinant G3Amy could produce and transfer maltotriose from starch.