Evaluation of different biomass materials as feedstock for fermentable sugar production

Production of the polysaccharide curdlan by anAgrobacteriumstrain grown on a plant biomass hydrolysate

Production of the commercially available polysaccharide curdlan by Agrobacterium sp. strain ECP-1, isolated as a mutant strain from ATCC 31749, on a medium containing a hydrolysate of the plant prairie cordgrass with selected ammonium phosphate concentrations was investigated for a period of 144 h. Although several ammonium phosphate concentrations supported curdlan production by the strain, the optimal concentration after 120 or 144 h was 3.3 mmol·L–1. Only ammonium phosphate concentrations of 1.1 or 8.7 mmol·L–1failed to support curdlan production by the strain after 120 or 144 h. Biomass production by strain ECP-1 on the hydrolysate-containing medium after 120 or 144 h was comparable, independent of the ammonium phosphate concentration present. The curdlan yield from the cordgrass hydrolysate indicated that the grass was an effective plant biomass substrate for polysaccharide production.

Fungal cellulase/xylanase production and corresponding hydrolysis using pretreated corn stover as substrates

Three pretreated corn stover (ammonia fiber expansion, dilute acid, and dilute alkali) were used as carbon source to culture Trichoderma reesei Rut C-30 for cellulase and xylanase production. The results indicated that the cultures on ammonia fiber expansion and alkali pretreated corn stover had better enzyme production than the acid pretreated ones. The consequent enzymatic hydrolysis was performed applying fungal enzymes on pretreated corn stover samples. Tukey's statistical comparisons exhibited that there were significant differences on enzymatic hydrolysis among different combination of fungal enzymes and pretreated corn stover. The higher sugar yields were achieved by the enzymatic hydrolysis of dilute alkali pretreated corn stover.

Bioethanol production from the macroalgae Sargassum spp

Macroalgae, an abundant and carbon-neutral renewable resource, with several species rich in carbohydrates are suitable for bioethanol production. This study focused on the pretreatment, enzyme saccharification and fermentation of Sargassum spp., a brown macroalgae for bioethanol production. The optimal acid pretreatment condition achieved in terms of glucose and reducing sugar yields was 3.4-4.6% (w/v) H2SO4 concentration, 115°C and 1.50h. The pretreated biomass was hydrolyzed with cellulase enzyme system supplemented with β-glucosidase. After fermentation by Saccharomyces cerevisiae at 40°C, pH of 4.5 for 48 h, the ethanol conversion rate of the enzyme hydrolysate reached 89%, which was markedly higher than the theoretical yield of 51% based on glucose as substrate. Since all the glucose was consumed during fermentation, other sugar sources might be present in the hydrolysate. The macroalgae, Sargassum spp., showed significant potential as a renewable feedstock for the production of bioethanol.

Automated assay for screening the enzymatic release of reducing sugars from micronized biomass

Background

To reduce the production cost of bioethanol obtained from fermentation of the sugars provided by degradation of lignocellulosic biomass (i.e., second generation bioethanol), it is necessary to screen for new enzymes endowed with more efficient biomass degrading properties. This demands the set-up of high-throughput screening methods. Several methods have been devised all using microplates in the industrial SBS format. Although this size reduction and standardization has greatly improved the screening process, the published methods comprise one or more manual steps that seriously decrease throughput. Therefore, we worked to devise a screening method devoid of any manual steps.

Results

We describe a fully automated assay for measuring the amount of reducing sugars released by biomass-degrading enzymes from wheat-straw and spruce. The method comprises two independent and automated steps. The first step is the making of "substrate plates". It consists of filling 96-well microplates with slurry suspensions of micronized substrate which are then stored frozen until use. The second step is an enzymatic activity assay. After thawing, the substrate plates are supplemented by the robot with cell-wall degrading enzymes where necessary, and the whole process from addition of enzymes to quantification of released sugars is autonomously performed by the robot. We describe how critical parameters (amount of substrate, amount of enzyme, incubation duration and temperature) were selected to fit with our specific use. The ability of this automated small-scale assay to discriminate among different enzymatic activities was validated using a set of commercial enzymes.

Conclusions

Using an automatic microplate sealer solved three main problems generally encountered during the set-up of methods for measuring the sugar-releasing activity of plant cell wall-degrading enzymes: throughput, automation, and evaporation losses. In its present set-up, the robot can autonomously process 120 triplicate wheat-straw samples per day. This throughput can be doubled if the incubation time is reduced from 24 h to 4 h (for initial rates measurements, for instance). This method can potentially be used with any insoluble substrate that is micronizable. A video illustrating the method can be seen at the following URL: http://www.youtube.com/watch?v=NFg6TxjuMWU