Utilization of sea water based media for the production and characterization of cellulase by Fusarium subglutinans MTCC 11891

Functional characterisation of a new halotolerant seawater active glycoside hydrolase family 6 cellobiohydrolase from a salt marsh

Realising a fully circular bioeconomy requires the valorisation of lignocellulosic biomass. Cellulose is the most attractive component of lignocellulose but depolymerisation is inefficient, expensive and resource intensive requiring substantial volumes of potable water. Seawater is an attractive prospective replacement, however seawater tolerant enzymes are required for the development of seawater-based biorefineries. Here, we report a halophilic cellobiohydrolase SMECel6A, identified and isolated from a salt marsh meta-exo-proteome dataset with high sequence divergence to previously characterised cellobiohydrolases. SMECel6A contains a glycoside hydrolase family 6 (GH6) domain and a carbohydrate binding module family 2 (CBM2) domain. Characterisation of recombinant SMECel6A revealed SMECel6A to be active upon crystalline and amorphous cellulose. Mono- and oligosaccharide product profiles revealed cellobiose as the major hydrolysis product confirming SMECel6A as a cellobiohydrolase. We show SMECel6A to be halophilic with optimal activity achieved in 0.5X seawater displaying 80.6 ± 6.93% activity in 1 × seawater. Structural predictions revealed similarity to a characterised halophilic cellobiohydrolase despite sharing only 57% sequence identity. Sequential thermocycling revealed SMECel6A had the ability to partially reversibly denature exclusively in seawater retaining significant activity. Our study confirms that salt marsh ecosystems harbour enzymes with attractive traits with biotechnological potential for implementation in ionic solution based bioprocessing systems.

Prospects of utilizing seawater as a reaction medium for pretreatment and saccharification of rice straw

The transition towards a bio-based economy has led to an unprecedented surge in fresh water consumption that renders biofuel a high water footprint product. The depleting fresh water resources have exacerbated the situation which necessitates the exploration of non-potable water for biorefinery purposes. In the current study, seawater is used as a plausible alternative reaction medium for pretreatment and saccharification of rice straw. Response Surface Methodology (RSM) based on Box-Behnken Design (BBD) was employed to model, predict and validate cellulose release and reducing sugar yield from rice straw subjected to microwave-NaOH pretreatment. The optimized pretreatment conditions were determined to be 8.54% substrate loading, 1.94% NaOH and 4.09 min which resulted in the maximum cellulose release of 65.43% and reducing sugar yield of 0.554 g/g. Several physico-chemical studies of the raw and pretreated biomass were carried out using bomb calorimetry, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) analysis and thermal gravimetric analysis (TGA) to examine the efficacy of pretreatment. Evidences of an apparent delignification was substantiated by the increase in surface area from 7.719 to 44.188 m² g^-1and pore volume from 0.039 to 0.071 mlg^-1 which was consistent with the decrease in energy density and distorted surface morphology of the pretreated biomass. Further, the FTIR revealed a reduced peak in the absorption spectral bands at 1636 cm^-1 which confirmed the pretreatment mediated degradation of lignin and hemicellulose. This finding provides evidence on the prospects of utilizing abundantly available seawater resource as a reaction medium for sustainable biofuel production.

Seawater-based biorefineries: A strategy to reduce the water footprint in the conversion of lignocellulosic biomass

Biorefineries are an essential step towards implementing a circular economy in the long term. They are based on renewable raw materials and must be designed holistically, recovering building blocks from being converted into several products. Lignocellulosic biomass is considered a critical pillar for a biologically based economy and a high value-added feedstock. The separation of the structural complexity that makes up the biomass allows the development of different product flows. Chemical, physical, and biological processes are evaluated for fractionation, hydrolysis, and fermentation processes in biorefineries; however, the volume of freshwater used affects water safety and increases the economic costs. Non-potable-resources-based technologies for biomass bioconversion are essential for biorefineries to become environmentally and economically sustainable systems. Studies are being carried out to substitute freshwater with seawater to reduce the water footprint. Accordingly, this review addresses a comprehensive discussion about seawater-based biorefineries focusing on lignocellulosic biomass conversion in biofuel and value-added products.

Efficient enzymatic saccharification of alkaline and ionic liquid-pretreated bamboo by highly active extremozymes produced by the co-culture of two halophilic fungi

Herein, we studied two strains of halophilic fungi (Aspergillus flavus and Aspergillus penicillioides) as potential potent sources of hydrolases under solid-state fermentation conditions. We found that the co-culture of these two fungal species was associated with maximal CMCase, FPase, xylanase, and β-xylosidase activity under optimized fermentation conditions. These enzymes functioned optimally at pH values from 9.0 to 10.0, at temperatures from 50 °C to 60 °C, and in the presence of 15-20% NaCl. These enzymes were also stable in metal salt solutions and the presence of ionic liquids. Reducing sugar yields following the cellulase-hemicellulase co-treatment of untreated, alkaline-pretreated, and ionic liquid-pretreated bamboo were higher than those associated with separate cellulase and hemicellulase treatments, thus confirming the synergistic activity of cellulase-hemicellulase co-treatment in the context of bamboo saccharification. These results indicate that these two fungi are promising hydrolase producers that can facilitate the bioconversion of bamboo biomass.

Improving β-glucosidase and xylanase production in a combination of waste substrate from domestic wastewater treatment system and agriculture residues

Cellulase and hemicellulase activities are considered to the major bottlenecks in the lignocellulosic biorefinery process, especially in an enzyme cocktail lacking β-glucosidase (BGL) and xylanase (XYL). In view of this issue, higher levels of BGL and XYL activities were obtained in the presence of wastewater and activated sludge as an induction medium mixed with 5% of rice straw by Hypocrea sp. W₆₃. The analysis of the ionic content showed that a relatively low sludge dose could enhance the production of BGL and XYL. Most importantly, compared to a medium using freshwater, the proportion of 1:10 sludge to wastewater, which contained nutrient elements, led to 3.4-fold BGL and 3.7-fold XYL production improvements. This research describes the reuse of substrates that are largely and continuously generated from domestic wastewater treatment systems and agriculture residues, which consequently leads to the development of a simultaneous enzyme production process for sustainable biorefinery practices.