Strain improvement of Trichoderma reesei Rut C-30 for increased cellulase production

The Role of Cell Wall Degrading Enzymes in Antagonistic Traits of Trichoderma virens Against Rhizoctonia solani

Background:

High antagonistic ability of different Trichoderma species against a diverse range of plant pathogenic fungi has led them to be used as a biological fungicide in agriculture. They can also promote plant growth, fertility, resistance to stress, and absorption of nutrients. They are also opportunistic and symbiotic pathogens, which can lead to the activation of plant defense mechanisms.

Objectives:

The aim of this present study was to investigate possible enhancement of lytic enzymes production and biocontrol activity of T. virens against Rhizoctonia solani through gamma radiation and to find the relationship between changes in lytic enzyme production and antagonistic activity of T. virens.

Material and Methods:

Dual culture conditions were used to evaluate the antagonistic effect of T. virens and its gamma mutants against R. solani. Then, their chitinase and cellulase activities were measured. For more detailed investigation of enzymes, densitometry pattern of the proteins was extracted from the T. virens wild-type and its mutants were obtained via SDS-polyacrylamide gel electrophoresis.

Results:

The mutant T.vi M₈, T. virens wild-type and mutant T.vi M₂₀ strains showed the maximum antagonistic effects against the pathogen, respectively. Data showed that the mutant T. vi M₈ reduced the growth of R. solani by 58 %. The mutants revealed significantly different (p<0.05) protein contents, chitinase and cellulase production (mg.mL^-1) and activity (U.mL-1) compared to the wild-type strain. The highest extracellular protein production in the supernatant of chitinase and cellulase TFM was observed for the T.vi M₁₁ and T.vi M₁₇ strains, respectively. The T.vi M₁₂ and wild-type strains secreted chitinase and cellulase significantly more than other strains did. Densitometry of SDS-PAGE gel bands indicated that both the amount and diversity of chitinase related proteins in the selected mutant (T. vi M₈) were far higher than those of the wild-type. The diversity of molecular weight of proteins extracted from the T. virens M₈ (20 proteins or bands) was very high compared to the wild-type (10 proteins) and mutant T.vi M₁₅ (2 proteins).

Conclusions:

Overall, there was a strong link between the diversity of various chitinase proteins and the antagonistic properties of the mutant M8.

The GATA-Type Transcriptional Factor Are1 Modulates the Expression of Extracellular Proteases and Cellulases in Trichoderma reesei

Trichoderma reesei is a biotechnologically important filamentous fungus with the remarkable ability to secrete large amounts of enzymes, whose production is strongly affected by both the carbon and nitrogen sources. While the carbon metabolism regulators are extensively studied, the regulation of enzyme production by the nitrogen metabolism regulators is still poorly understood. In this study, the GATA transcription factor Are1, which is an orthologue of the Aspergillus global nitrogen regulator AREA, was identified and characterized for its functions in regulation of both protease and cellulase production in T. reesei. Deletion of the are1 gene abolished the capability to secrete proteases, and complementation of the are1 gene rescued the ability to produce proteases. Quantitative RT-PCR analysis revealed that the transcripts of protease genes apw1 and apw2 were also significantly reduced in the Δare1 strain when grown in the medium with peptone as the nitrogen source. In addition, deletion of are1 resulted in decreased cellulase production in the presence of (NH₄)₂SO₄. Consistent with the reduction of cellulase production, the transcription levels of the major cellulase genes, including cbh1, cbh2, egl1, and egl2, were dramatically decreased in Δare1. Sequence analysis showed that all promoter regions of the tested protease and cellulase genes contain the consensus GATA elements. However, the expression levels of the major cellulase transcription activator Xyr1 and the repressor Cre1 had no significant difference between Δare1 and the parental strain QM9414, indicating that the regulatory mechanism deserves further investigation. Taken together, these results demonstrate the important role of Are1 in the regulation of protease and cellulase production in T. reesei, although these processes depend on the kind of nitrogen sources. The findings in this study contribute to the understanding of the regulation network of carbon and nitrogen sources in filamentous fungi.

Comprehensive studies on optimization of cellulase and xylanase production by a local indigenous fungus strain via solid state fermentation using oil palm frond as substrate

The high cost of cellulases remains the most significant barrier to the economical production of bio-ethanol from lignocellulosic biomass. The goal of this study was to optimize cellulases and xylanase production by a local indigenous fungus strain (Aspergillus niger DWA8) using agricultural waste (oil palm frond [OPF]) as substrate. The enzyme production profile before optimization indicated that the highest carboxymethyl cellulose (CMCase), filter paper (FPase), and xylanase activities of 1.06 U/g, 2.55 U/g, and 2.93 U/g were obtained on day 5, day 4, and day 5 of fermentation, respectively. Response surface methodology was used to study the effects of several key process parameters in order to optimize cellulase production. Of the five physical and two chemical factors tested, only moisture content of 75% (w/w) and substrate amount of 2.5 g had statistically significant effect on enzymes production. Under optimized conditions of 2.5 g of substrate, 75% (w/w) moisture content, initial medium of pH 4.5, 1 × 10⁶ spores/mL of inoculum, and incubation at ambient temperature (±30°C) without additional carbon and nitrogen, the highest CMCase, FPase, and xylanase activities obtained were 2.38 U/g, 2.47 U/g, and 5.23 U/g, respectively. Thus, the optimization process increased CMCase and xylanase production by 124.5 and 78.5%, respectively. Moreover, A. niger DWA8 produced reasonably good cellulase and xylanase titers using OPF as the substrate when compared with previous researcher finding. The enzymes produced by this process could be further use to hydrolyze biomass to generate reducing sugars, which are the feedstock for bioethanol production.

Regular enzyme recovery enhances cellulase production by Trichoderma reesei in fed-batch culture

OBJECTIVE

To protect the enzymes during fed-batch cellulase production by means of partial enzyme recovery at regular intervals.

RESULTS

Extracellular enzymes were partially recovered at the intervals of 1, 2, or 3 days. Mycelia were also removed to avoid contamination. Increases in the total harvested cellulase (24-62%) and β-glucosidase (22-76%) were achieved. In fermentor cultivation when the enzymes were recovered every day with 15% culture broth. The total harvested cellulase and β-glucosidase activity increased by 43 and 58%, respectively, with fungal cell concentration maintained at 3.5-4.5 g l^-1.

CONCLUSION

Enzyme recovery at regular intervals during fed-batch cellulase cultivation could protect the enzyme in the culture broth and enhance the enzyme production when the fungal cell concentration is maintained in a reasonable range.

Harnessing the hydrolytic potential of phytopathogenic fungus Phoma exigua ITCC 2049 for saccharification of lignocellulosic biomass

Phytopathogenic fungi develop unique systems for fast invasion by producing hydrolases, which may be explored as a source of hydrolytic enzymes for biofuel research. The present work deals with evaluation of a potato pathogen Phoma exigua ITCC 2049 for its potential to produce cellulase and xylanase enzyme. Taguchi methodology was applied to reveal the influence and contribution of five important factors (carbon source, organic and inorganic nitrogen source, surfactant, and pH) on hydrolytic enzyme production by Phoma. Cultivation of fungus under optimized condition produced endoglucanase (37.00 IU/ml), FPase (1.13 IU/ml), β-glucosidase (2.67 IU/ml) and xylanase (24.92 IU/ml) within 8 days of submerged fermentation. Saccharification of biopretreated Parthenium and paddy straw with cocktail of Phoma secretome supplemented with commercial β-glucosidase resulted in the significantly higher reducing sugar yield (651.04-698.11 mg/gds). This study proves the potential of Phoma as an alternative source of enzymes for biomass saccharification.

Development of a β-glucosidase hyperproducing mutant by combined chemical and UV mutagenesis

The extracellular β-glucosidase from microorganisms is generally produced in low levels. Therefore, in this study, a β-glucosidase hyperproducing mutant was developed by multiple exposures of ethyl methyl sulfonate (EMS) and ultraviolet (UV) radiation (both individually and jointly) to Bacillus subtilis strain (PS). The developed mutants were screened, selected and characterized. The mutant, PS-UM1 developed after UV exposure alone, indicated a small increase in β-glucosidase production (718 U/l) in comparison to the wild-type strain, PS (675 U/l). The mutant, PS-CM5 developed after EMS exposure alone, displayed a slightly better production (762 U/l) than both the above strains. However, after exposure of the wild-type strain to both UV and EMS mutagens jointly, a better mutant (PS-CM5-UM3) was developed with 1.2-fold increase in production (806 U/l). Further, optimization of culture conditions by classical "one-variable-at-a-time" approach was done to determine the optimum, pH, temperature and nitrogen sources. The selected mutant (PS-CM5-UM3) produced up to 1,797 U/l enzyme and was found to be stable for ten generations. The β-glucosidase from the selected mutant (PS-CM5-UM3) was concentrated and purified using ammonium sulfate, dialysis and size-exclusion chromatography. The enzyme displayed maximal activity at 60 °C and it was found to be fairly stable at temperatures up to 70 °C for 30 min. Its molecular weight was determined to be around 60 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).

Is an organic nitrogen source needed for cellulase production by Trichoderma reesei Rut-C30?

The effect of organic and inorganic nitrogen sources on Trichoderma reesei Rut-C30 cellulase production was investigated in submerged cultivations. Stirred tank bioreactors and shake flasks, with and without pH control, respectively, were employed. The experimental design involved the addition of individual organic nitrogen sources (soy peptone, glutamate, glycine and alanine) within a basal medium containing Avicel (i.e. micro crystalline cellulose) and ammonium sulphate. It was found that in the shake flask experiments, the highest cellulase activities (~0.1 ± 0.02 FPU ml(-1)) were obtained with media containing soy peptone (3-6 g l(-1)) and glutamate (3.6 g l(-1)). However, these improvements in the cellulase titers in the presence of the organic nitrogen sources appeared to be related to smaller changes in the pH of the medium. This was confirmed using stirred tank bioreactors with pH control. No significant differences were observed in the highest cellulase titers and the protein pattern (according to the SDS-PAGE) of supernatants from pH controlled stirred tank bioreactor cultivations, when different nitrogen sources were used in the medium. Here the cellulase activities (~1.0 ± 0.2 FPU ml(-1)) were also much greater (8-150 times) than in shake flask cultivation. Consequently, the addition of ammonium sulphate as sole nitrogen source to Avicel basal medium is recommended when performing cultivations in stirred tank bioreactors with strict pH controlled conditions.