Detoxification of sugarcane bagasse hydrolysate with different adsorbents to improve the fermentative process.

Second generation ethanol has the prospect of becoming an important bioenergy alternative. The development of this technology is associated with the lignocellulosic materials' use, with emphasis on agricultural and agroindustrial by-products from which fermentable sugar can be produced. The acid hydrolysis depolymerizes the hemicellulose releasing mainly xylose. Subsequently, the cellulose can be converted into glucose by enzymatic hydrolysis. However, the acid hydrolysis produces toxic compounds, such as furan derivatives, phenolics, and organic acids, which are harmful to fermentative microorganisms. This study investigated different acid concentrations in the sulfuric acid hydrolysis of sugarcane bagasse (1- 5% m/v) and the use of adsorbents with the prerogative to improve the acid hydrolysate (AH) quality for microbial ethanolic fermentation. Cell growth and fermentative yield of Saccharomyces cerevisiae (PE-2) and Scheffersomyces stipitis (NRRL Y-7124) were evaluated. AH was used as a source of pentoses (17.7 g L-1) and molasses (ME) sugarcane as source of hexoses (47 g L-1). The following adsorbents were used: activated charcoal, clay, hydrotalcite and active and inactive cells of PE-2 and NRRL Y-7124, at concentrations ranging (1 - 8% m/v). Results of cell growth and chemical characterization allowed to select the most effective adsorbents with emphasis for active cells that removed 66% furfural and 51% 5-(hydroxymethyl) furfural) (5-HMF) and alcoholic productivity of 23.5 g L-1 in AH and ME substrates, in the presence of mixed culture. These results indicate the application of active yeast cells in the detoxification of acid hydrolysates of the sugarcane bagasse previously to the fermentation.

Timely Addition of Glutathione for Its Interaction with Deoxypentosone To Inhibit the Aqueous Maillard Reaction and Browning of Glycylglycine-Arabinose System.

The inhibitory effects of glutathione (GSH) and oxiglutathione (GSSG) on Maillard browning were compared, and it was clarified that free sulfhydryl was the key substance for the inhibition. The Amadori rearrangement product (ARP) derived from glycylglycine (Gly-Gly) and arabinose (Ara) was prepared by aqueous Maillard reaction, and LC-MS/MS was used to investigate the reaction products of GSH and purified ARP. Reaction between GSH and deoxypentosone (DP) was found to alter the pathway of aqueous Maillard reaction, which reduced the production of glyoxal, methylglyoxal, and furfural and thereby inhibited the formation of melanoidins. To determine the optimal conditions for browning inhibition, a stepwise increase of temperature was used to prepare Maillard reaction products (MRPs). The results showed that the optimum browning inhibitory effect was obtained by adding GSH after Gly-Gly and Ara heating at 80 °C for 60 min.

Permeation of aldopentoses and nucleosides through fatty acid and phospholipid membranes: implications to the origins of life.

Permeation of aldopentoses and nucleosides through fatty acid and phospholipid membranes was investigated by way of molecular dynamics simulations. Calculated permeability coefficients of membranes to aldopentoses, which exist predominantly in the pyranose form, are in a very good agreement with experimental results. The unexpected preferential permeation of ribose, compared to its diastereomers, found by Sacerdote and Szostak, is explained in terms of inter- and intramolecular interactions involving hydroxyl groups. In aqueous solution, these groups favor the formation of intermolecular hydrogen bonds with neighboring water molecules. Inside the membrane, however, they form intramolecular hydrogen bonds, which in ribose are arranged in a chain. In its diastereomers this chain is broken, which yields higher free energy barrier to transfer through membranes. Faster permeation of ribose would lead to its preferential accumulation inside cells if sugars were converted sufficiently quickly to nonpermeable derivatives. An estimate for the rate of such reaction was derived. Preferential accumulation of ribose would increase the probability of correct monomers' incorporation during synthesis of nucleic acids inside protocells. The same mechanism does not apply to nucleosides or their activated derivatives because sugars are locked in the furanose form, which contains fewer exocyclic hydroxyl groups than does pyranose. The results of this study underscore concerted early evolution of membranes and the biochemical processes that they encapsulated.

Dissecting and engineering metabolic and regulatory networks of thermophilic bacteria for biofuel production.

Interest in thermophilic bacteria as live-cell catalysts in biofuel and biochemical industry has surged in recent years, due to their tolerance of high temperature and wide spectrum of carbon-sources that include cellulose. However their direct employment as microbial cellular factories in the highly demanding industrial conditions has been hindered by uncompetitive biofuel productivity, relatively low tolerance to solvent and osmic stresses, and limitation in genome engineering tools. In this work we review recent advances in dissecting and engineering the metabolic and regulatory networks of thermophilic bacteria for improving the traits of key interest in biofuel industry: cellulose degradation, pentose-hexose co-utilization, and tolerance of thermal, osmotic, and solvent stresses. Moreover, new technologies enabling more efficient genetic engineering of thermophiles were discussed, such as improved electroporation, ultrasound-mediated DNA delivery, as well as thermo-stable plasmids and functional selection systems. Expanded applications of such technological advancements in thermophilic microbes promise to substantiate a synthetic biology perspective, where functional parts, module, chassis, cells and consortia were modularly designed and rationally assembled for the many missions at industry and nature that demand the extraordinary talents of these extremophiles.

Lagrangian molecular dynamics using selected conformational degrees of freedom, with application to the pseudorotation dynamics of furanose rings.

Using internal conformational degrees of freedom for biopolymers as natural variables, and introducing a Lagrangian dynamics approach, one can simulate time-dependent processes over a much longer time scale than in classical Newtonian molecular dynamics (MD) techniques. Two factors contribute to this: a substantial reduction in the number of degrees of freedom and a very large increase in the size of the time step. We present the Lagrangian equations of motion for repuckering transitions in model furanose (F), ribose (R), and 2'-deoxyribose (dR) ring systems using the pseudorotation phase angle as the single dynamic variable. As in most Lagrangian analyses, the effective masses for the R and dR models are dependent on conformation, and we test the behavior of this variable mass (VM) model. Since the variation in effective mass is small, the VM model is compared with a simplified constant mass (CM) model, which is shown to be an excellent approximation. The equations of motion for the CM and VM models are integrated with the leapfrog and the iterative leapfrog algorithms, respectively. The Lagrangian dynamics approach reduces the number of degrees of freedom from about 40 to 1, and allows the use of time steps on the order of 20 fs, about an order of magnitude greater than is used in conventional MD simulations.