Production of cellulosic ethanol and enzyme from waste fiber sludge using SSF, recycling of hydrolytic enzymes and yeast, and recombinant cellulase-producing Aspergillus niger

Solid-state fermentation of Apocynum venetum L. by Aspergillus niger: Effect on phenolic compounds, antioxidant activities and metabolic syndrome-associated enzymes

This study aimed to evaluate the effect of solid-state fermentation (SSF) with Aspergillus niger on the total phenolic content (TPC), the total flavonoid content (TFC), individual phenolic contents, and antioxidant and inhibitory activities against metabolic syndrome-associated enzymes in an ethanol extract from Apocynum venetum L. (AVL). TPC, TFC, and the contents of quercetin and kaempferol during SSF were 1.52-, 1.33-, 3.64-, and 2.22-fold higher than those of native AVL in the ethyl acetate (EA) subfraction of the ethanol extract. The ABTS·⁺, DPPH· scavenging, and inhibitory activities against α-glucosidase and pancreatic lipase were found to be highest in the EA subfraction. Fermentation significantly increased the ABTS radical cation, DPPH radical scavenging, and pancreatic lipase inhibitory activities by 1.33, 1.39, and 1.28 times, respectively. TPC showed a significantly positive correlation with antioxidant activities or inhibition against metabolic syndrome-associated enzymes. This study provides a theoretical basis for producing tea products with enhanced antioxidant, antidiabetic, and antihyperlipidemic activities.

Integrating 1G with 2G Bioethanol Production by Using Distillers’ Dried Grains with Solubles (DDGS) as the Feedstock for Lignocellulolytic Enzyme Production

First-generation (1G) bioethanol is one of the most used liquid biofuels in the transport industry. It is generated by using sugar- or starch-based feedstocks, while second-generation (2G) bioethanol is generated by using lignocellulosic feedstocks. Distillers’ dried grains with solubles (DDGS) is a byproduct of first-generation bioethanol production with a current annual production of 22.6 million tons in the USA. DDGS is rich in fiber and valuable nutrients contents, which can be used to produce lignocellulolytic enzymes such as cellulases and hemicellulases for 2G bioethanol production. However, DDGS needs a pretreatment method such as dilute acid, ammonia soaking, or steam hydrolysis to release monosaccharides and short-length oligosaccharides as fermentable sugars for use in microbial media. These fermentable sugars can then induce microbial growth and enzyme production compared to only glucose or xylose in the media. In addition, selection of one or more suitable microbial strains, which work best with the DDGS for enzyme production, is also needed. Media optimization and fermentation process optimization strategies can then be applied to find the optimum conditions for the production of cellulases and hemicellulases needed for 2G bioethanol production. Therefore, in this review, a summary of all such techniques is compiled with a special focus on recent findings obtained in previous pieces of research conducted by the authors and by others in the literature. Furthermore, a comparison of such techniques applied to other feedstocks and process improvement strategies is also provided. Overall, dilute acid pretreatment is proven to be better than other pretreatment methods, and fermentation optimization strategies can enhance enzyme production by considerable folds with a suitable feedstock such as DDGS. Future studies can be further enhanced by the technoeconomic viability of DDGS as the on-site enzyme feedstock for the manufacture of second-generation bioethanol (2G) in first-generation (1G) ethanol plants, thus bridging the two processes for the efficient production of bioethanol using corn or other starch-based lignocellulosic plants.

Press water from the mechanical drying of Douglas-fir wood chips has multiple beneficial effects on lignocellulolytic fungi

Background

The mechanical drying of wood chips is an innovative method that improves the heating value of sawmill by-products in an energy-efficient continuous process. The liquid that comes out of the wood chips as press water (PW), however, contains a variety of undissolved as well as dissolved organic substances. The disposal of the PW as wastewater would generate additional costs due to its high organic load, offsetting the benefits in energy costs associated with the enhanced heating value of the wood chips. Our research explored if the organic load in PW could be utilized as a substrate by cellulolytic filamentous fungi. Hence, using the industrially relevant Ascomycete Trichoderma reesei RUT-C30 as well as several Basidiomycete wood-rotting fungi, we examined the potential of press water obtained from Douglas-fir wood chips to be used in the growth and enzyme production media.

Results

The addition of PW supernatant to liquid cultures of T. reesei RUT-C30 resulted in a significant enhancement of the endoglucanase and endoxylanase activities with a substantially shortened lag-phase. A partial replacement of Ca²⁺, Mg²⁺, K⁺, as well as a complete replacement of Fe²⁺, Mn²⁺, Zn²⁺ by supplementing PW of the liquid media was achieved without negative effects on enzyme production. Concentrations of PW above 50% showed no adverse effects regarding the achievable endoglucanase activity but affected the endoxylanase activity to some extent. Exploring the enhancing potential of several individual PW components after chemical analysis revealed that the observed lag-phase reduction of T. reesei RUT-C30 was not caused by the dissolved sugars and ions, nor the wood particles in the PW sediment, suggesting that other, so far non-identified, compounds are responsible. However, also the growth rate of several basidiomycetes was significantly enhanced by the supplementation of raw PW to the agar medium. Moreover, their cultivation in liquid cultures reduced the turbidity of the PW substantially.

Conclusions

PW was identified as a suitable media supplement for lignocellulolytic fungi, including the cellulase and xylanase producer T. reesei RUT-C30 and several wood-degrading basidiomycetes. The possibility to replace several minerals, trace elements and an equal volume of fresh water in liquid media with PW and the ability of fungal mycelia to filter out the suspended solids is a promising way to combine biological wastewater treatment with value-adding biotechnological applications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40694-022-00141-y.

Improving the Bioremediation and in situ Production of Biocompounds of a Biodiesel-Contaminated Soil

We aimed to produce simultaneously biosurfactants and lipases in solid state fermentation (SSF) using Aspergillus niger, followed by the use of the fermented media on the bioremediation of oily contaminated soil, in order to valuate agro industrial residuals and reduce the contamination. The biocompounds were produced using wheat bran and corncob (80:20), 5% of soybean oil and 0.5% of sugar cane molasses in SSF for 4 d, producing 4.58 ± 0.69 UE of emulsifying activity and 7.77 ± 1.52 U of lipolytic activity. This fermented media was used in the bioremediation of a 20% biodiesel contaminated soil, evaluating for 90 d microbial growth, contaminant degradation, and production of lipases and biosurfactants in soils. Six experimental strategies (natural attenuation; biostimulation + bioaugmentation + biocompounds; biostimulation + biosurfactant; biocompounds extract; biostimulation; adsorption of contaminant) were realized. The highest degradation of contaminant was verified in 90 d, of 74.40 ± 1.76%, and the production of biosurfactants and lipases in situ in the soil was found in 30 d (6.02 ± 0.24% of reduction in surface tension and 6.62 ± 0.17 UL of lipid activity in soil) for the same experiment (biostimulation + bioaugmentation + biocompounds). The addition of biostimulation + biosurfactant promotes higher biodegradation (66.00 ± 0.92%) of the contaminant than the biocompounds extract (59.58 ± 0.34%). The use of a solid fermented culture medium containing both biocompounds was feasible for the treatment of contaminants, demonstrating the potential for environmental application without the need for purification processes.

A yeast metabolome-based model for an ecotoxicological approach in the management of lignocellulosic ethanol stillage

Lignocellulosic bioethanol production results in huge amounts of stillage, a potentially polluting by-product. Stillage, rich in heavy metals and, mainly, inhibitors, requires specific toxicity studies to be adequately managed. To this purpose, we applied an FTIR ecotoxicological bioassay to evaluate the toxicity of lignocellulosic stillage. Two weak acids and furans, most frequently found in lignocellulosic stillage, have been tested in different mixtures against three Saccharomyces cerevisiae strains. The metabolomic reaction of the test microbes and the mortality induced at various levels of inhibitor concentration showed that the strains are representative of three different types of response. Furthermore, the relationship between concentrations and FTIR synthetic stress indexes has been studied, with the aim of defining a model able to predict the concentrations of inhibitors in stillage, resulting in an optimized predictive model for all the strains. This approach represents a promising tool to support the ecotoxicological management of lignocellulosic stillage.

Construction of recombinant sestc Saccharomyces cerevisiae for consolidated bioprocessing, cellulase characterization, and ethanol production by in situ fermentation

Bioethanol is an important oil substitute produced by the sugar fermentation process. To improve the efficiency of cellulase expression of Saccharomyces cerevisiae, a eukaryotic expression vector harboring a single-enzyme-system-three-cellulase gene (sestc) was integrated into the S. cerevisiae genome by the protoplast method. Using PCR screening, RT-PCR, and “transparent circle” detection, several recombinant S. cerevisiae strains, capable of efficiently expressing the heterogeneous cellulase, were selected. The total activity of cellulase, endo-β-D-glucanase, exo-β-D-glucanase, and xylanase of the recombinant S. cerevisiae transformant (designated number 14) was 1.1, 378, 1.44, and 164 U ml⁻¹, respectively, which was 27.5-, 63-, 24-, and 19-fold higher than that of the wild-type strain. The concentration of ethanol produced by the engineered S. cerevisiae strain was 8.1 gl⁻¹, with wheat bran as the carbon source, under submerged conditions; this was 57.86-fold higher than that produced by the wild-type strain (0.14 gl⁻¹).

Integrated bioconversion of pulp and paper primary sludge to second generation bioethanol using Saccharomyces cerevisiae ATCC 26602

Primary sludge, from different pulp and paper mills, was used as feedstock in simultaneous saccharification and fermentation (SSF) processes to produce ethanol. SSF was carried out with Saccharomyces cerevisiae ATCC 26602 yeast and NS 22192 enzymatic extract using 150gL(-1) of carbohydrates (CH) from primary sludge. The effect of sterilization, reduction of enzyme dosage and fed-batch vs. batch conditions were studied. The removal of sterilization can be considered since no contamination or atypical by-products were observed, although SSF efficiency slightly decreased. The reduction of the enzyme dosage from 35 to 15FPUgCH(-1) was successful. Despite of initial mixing difficulties, batch SSF enabled higher ethanol concentration (41.7gL(-1)), conversion yield (48.9%) and productivity (0.78gL(-1)h(-1)), compared to the fed-batch process at the same conditions of low enzyme dosage of 5FPUgCH(-1) and high solids content of 21.7%, rarely found in literature.

Fermentation Optimization and Unstructured Kinetic Model for Cellulase Production by Rhizopus stolonifer var. reflexus TP-02 on Agriculture By-Products

Agricultural by-products, rice straw, wheat bran juice, and soybean residue, were used as substrates for cellulase production using Rhizopus stolonifer var. reflexus TP-02. The culture medium was optimized though uniform design experimentation during shaking flask fermentation, and the ideal formulation obtained for filter paper enzyme (FPase) production was 10 % bran diffusion juice, 1 % rice straw, 0.17 % urea, 0.17 % soybean residue, 0.11 % KH2PO4, and 0.027 % Tween 80, and the maximal FPase activity in the culture supernatant was 13.16 U/mL at an incubation time of 3 days. A kinetic model for cellulase production in batch fermentation was subsequently developed. The unstructured kinetic model considered three responses, namely biomass, cellulase, and sugar. Models for the production of three types of cellulase components (i.e., endoglucanases, cellobiohydrolases, and β-glucosidases) were established to adequately describe the cellulase production pattern. It was found that the models fitted the experimental data well under pH 5.0 and 6.0, but only the avicelase production model predicted the experimental data under pH-uncontrolled conditions.