Krisztina Kovács

Comparative enzymatic hydrolysis of pretreated spruce by supernatants, whole fermentation broths and washed mycelia of Trichoderma reesei and Trichoderma atroviride

Cellulase and beta-glucosidase production on steam pretreated spruce (SPS) with Trichoderma reesei Rut C30, Trichoderma atroviride TUB F-1505 and TUB F-1663 was investigated. The enzymes were compared in term of activity, temperature optima and hydrolytic capacity. The T. atroviride cellulases proved to have lower temperature optima for filter paper activity (FPA) assay (50 degrees C) and for hydrolysis of SPS (40 degrees C) than the Rut C30 enzymes (60 degrees C for FPA and 50 degrees C for hydrolysis). Due to high levels of extracellular beta-glucosidases, the T. atroviride enzyme supernatants hydrolyzed the washed SPS to glucose more efficiently than the enzymes produced by T. reesei. On the other hand, when the whole fermentation broths were used instead of the supernatants, thus the mycelium bound enzymes were also present, the hydrolytic capacity of T. reesei Rut C30 was enhanced by approximately 200%, while an improvement of only 15% was observed in case of the T. atroviride isolates.

Enzymatic hydrolysis of steam-pretreated lignocellulosic materials with Trichoderma atroviride enzymes produced in-house

BackgroundImprovement of the process of cellulase production and development of more efficient lignocellulose-degrading enzymes are necessary in order to reduce the cost of enzymes required in the biomass-to-bioethanol process.ResultsLignocellulolytic enzyme complexes were produced by the mutant Trichoderma atroviride TUB F-1663 on three different steam-pretreated lignocellulosic substrates, namely spruce, wheat straw and sugarcane bagasse. Filter paper activities of the enzymes produced on the three materials were very similar, while β-glucosidase and hemicellulase activities were more dependent on the nature of the substrate. Hydrolysis of the enzyme preparations investigated produced similar glucose yields. However, the enzymes produced in-house proved to degrade the xylan and the xylose oligomers less efficiently than a commercial mixture of cellulase and β-glucosidase. Furthermore, accumulation of xylose oligomers was observed when the TUB F-1663 supernatants were applied to xylan-containing substrates, probably due to the low β-xylosidase activity of the enzymes. The efficiency of the enzymes produced in-house was enhanced by supplementation with extra commercial β-glucosidase and β-xylosidase. When the hydrolytic capacities of various mixtures of a commercial cellulase and a T. atroviride supernatant produced in the lab were investigated at the same enzyme loading, the glucose yield appeared to be correlated with the β-glucosidase activity, while the xylose yield seemed to be correlated with the β-xylosidase level in the mixtures.ConclusionEnzyme supernatants produced by the mutant T. atroviride TUB F-1663 on various pretreated lignocellulosic substrates have good filter paper activity values combined with high levels of β-glucosidase activities, leading to cellulose conversion in the enzymatic hydrolysis that is as efficient as with a commercial cellulase mixture. On the other hand, in order to achieve good xylan conversion, the supernatants produced by the mutant have to be supplemented with additional β-xylosidase activity.

Process Design and Economics of On-Site Cellulase Production on Various Carbon Sources in a Softwood-Based Ethanol Plant

On-site cellulase enzyme fermentation in a softwood-to-ethanol process, based on SO2-catalysed steam pretreatment followed by simultaneous saccharification and fermentation, was investigated from a techno-economic aspect using Aspen Plus© and Aspen Icarus Process Evaluator© softwares. The effect of varying the carbon source of enzyme fermentation, at constant protein and mycelium yields, was monitored through the whole process. Enzyme production step decreased the overall ethanol yield (270 L/dry tonne of raw material in the case of purchased enzymes) by 5–16 L/tonne. Capital cost was found to be the main cost contributor to enzyme fermentation, constituting to 60–78% of the enzyme production cost, which was in the range of 0.42–0.53 SEK/L ethanol. The lowest minimum ethanol selling prices (4.71 and 4.82 SEK/L) were obtained in those scenarios, where pretreated liquid fraction supplemented with molasses was used as carbon source. In some scenarios, on-site enzyme fermentation was found to be a feasible alternative.

l-leucine aminopeptidase production by filamentous Aspergillus fungi.

Aims:  To screen various filamentous fungi belonging to Aspergillus spp. producing leucine and methionine aminopeptidases.

Production of chitinolytic enzymes with Trichoderma longibrachiatum IMI 92027 in solid substrate fermentation.

Thirty Trichoderma strains representing 15 species within the genus were screened for extracellular production of chitinolytic enzymes in solid substrate fermentation. Trichoderma longibrachiatum IMI 92027 (ATCC 36838) gave the highest yield (5.0 IU/g of dry matter of substrate) after 3 d of fermentation on wheat bran-crude chitin (9:1 mixture) medium. The optimal moisture content (66.7%), chitin content (20%), initial pH of the medium (2.0–5.0), and time course (5 d) of solid substrate fermentation were determined for strain IMI 92027. Cellulase, xylanase, α-amylase, and β-xylosidase activities were also detected. The pH and temperature optima of the chitinase complex of T. longibrachiatum IMI 92027 were 4.5 and 55°C, respectively. The enzyme totally lost its activity at 70°C in 5 min in the absence of the substrate but retained about 15% of its initial activity even at 70°C after a 60-min incubation in the presence of solid substrate fermentation solids. Purification of protein extract from the solid substrate fermentation material revealed high chitinolytic activities between pI 5.9 and 4.8, where N-acetyl-β-d-hexosaminidase and chitinase peaks have been found in the same pI range. Two chitinases of 43.5 and 30 kDa were purified at acidic pI.

Effect of a trifluoromethyl group on molecular structure: Competitive mono- and dilithiation of 1-[(trifluoromethyl)phenyl]pyrroles

Abstract Depending on the conditions used during the lithiation and subsequent carboxylation of 1-[(trifluoromethyl)phenyl]pyrroles the mono- and the dicarboxylated derivatives were selectively prepared. The regioselective formation of the monocarboxylic acids could be rationalized in the light of the data collected from the literature. Explanation of the other phenomena, such as regioselective dilithiation and the strong effect of the trifluoromethyl group on the structure and aromaticity of the pyrrole ring in the ortho position, has been elucidated by the aid of molecular modelling and single crystal X-Ray measurements.

Commentary: Oxytocin-gaze positive loop and the coevolution of human–dog bonds

It has been proposed that evolution of dogs have led to a set of changes, which made them functionally similar to humans in some cognitive, behavioral, and social aspects (Topal et al., 2005; MacLean and Hare, 2015). Searching for these similarities, Nagasawa et al. (2015) hypothesize an oxytocin-mediated positive loop, which developed through the coevolution of human–dog bonding. To test this hypothesis, they conducted a highly original experiment, examining the effects of a 30-min human–dog interaction on oxytocin-secretion in both owners and dogs, and investigating which characteristics of the interaction modulated the oxytocin change (experiment 1). A unique feature of the study is that the same experiment was repeated with hand-reared wolves and their owners to evaluate whether the proposed oxytocin loop was specific to the human–dog interaction. In a following experiment (experiment 2), they administered oxytocin to dogs, and recoded changes in social behavior, and effects of the behavioral change on the owners urinary oxytocin levels.