One-pot synthesis of cellobiose from sucrose using sucrose phosphorylase and cellobiose phosphorylase co-displaying Pichia pastoris as a reusable whole-cell biocatalyst.

Cellobiose has received increasing attention in various industrial sectors, ranging from food and feed to cosmetics. The development of large-scale cellobiose applications requires a cost-effective production technology as currently used methods based on cellulose hydrolysis are costly. Here, a one-pot synthesis of cellobiose from sucrose was conducted using a recombinant Pichia pastoris strain as a reusable whole-cell biocatalyst. Thermophilic sucrose phosphorylase from Bifidobacterium longum (BlSP) and cellobiose phosphorylase from Clostridium stercorarium (CsCBP) were co-displayed on the cell surface of P. pastoris via a glycosylphosphatidylinositol-anchoring system. Cells of the BlSP and CsCBP co-displaying P. pastoris strain were used as whole-cell biocatalysts to convert sucrose to cellobiose with commercial thermophilic xylose isomerase. Cellobiose productivity significantly improved with yeast cells grown on glycerol compared to glucose-grown cells. In one-pot bioconversion using glycerol-grown yeast cells, approximately 81.2 g/L of cellobiose was produced from 100 g/L of sucrose, corresponding to 81.2% of the theoretical maximum yield, within 24 h at 60 °C. Moreover, recombinant yeast cells maintained a cellobiose titer > 80 g/L, even after three consecutive cell-recycling one-pot bioconversion cycles. These results indicated that one-pot bioconversion using yeast cells displaying two phosphorylases as whole-cell catalysts is a promising approach for cost-effective cellobiose production.

Deciphering the colonic fermentation characteristics of agavin and digestion-resistant maltodextrin in a simulated batch fermentation system.

Gut microbial fermentation of soluble dietary fibers promotes general and substrate-specific health benefits. In this study, the fermentation characteristics of two soluble branched-dietary fibers, namely, agavin (a type of agave fructans) and digestion-resistant maltodextrin (RD) were investigated against cellulose, using a simulated colonic fermenter apparatus employing a mixed culture of swine fecal bacteria. After 48 h of complete fermentation period, the microbial composition was different among all groups, where Bifidobacterium spp. and Lactobacillus spp. dominated the agavin treatment, while the members of the families Lachnospiraceae and Prevotellaceae dominated the RD treatment. Agavin treatment exhibited a clearly segregated two-phased prolonged fermentation trend compared to RD treatment as manifested by the fermentation rates. Further, the highest short-chain fatty acids production even at the end of the fermentation cycle, acidic pH, and the negligible concentration of ammonia accumulation demonstrated favorable fermentation attributes of agavin compared to RD. Therefore, agavin might be an effective and desirable substrate for the colonic microbiota than RD with reference to the expressed microbial taxa and fermentation attributes. This study revealed a notable significance of the structural differences of fermentable fibers on the subsequent fermentation characteristics.

Comparison of the prebiotic properties of native chicory and synthetic inulins using swine fecal cultures.

Inulin-type fructans are known to exert different effects on the fermentation profile depending on the average and range of the degree of polymerization (DP). Here, swine fecal cultures were used to investigate the prebiotic properties of native chicory inulin (NIN), extracted from the chicory root, and synthetic inulin (SIN), which has a narrower DP distribution than NIN. Both NIN and SIN showed prebiotic effects, but NIN exhibited a significant decrease in pH and increase in the production of propionate and butyrate compared to SIN. There were also differences in the production of succinate and lactate, the precursors of propionate and butyrate, and the relative abundance of associated genes. Furthermore, NIN induced the growth of certain species of Bifidobacterium and Lactobacillus more strongly than SIN. These results suggest that NIN and SIN exhibit different prebiotic properties due to differences in DP, and that NIN might be more beneficial to host health.

Response to Comment on "A bacterium that degrades and assimilates poly(ethylene terephthalate)".

Yang et al suggest that the use of low-crystallinity poly(ethylene terephthalate) (PET) exaggerates our results. However, the primary focus of our study was identifying an organism capable of the biological degradation and assimilation of PET, regardless of its crystallinity. We provide additional PET depolymerization data that further support several other lines of data showing PET assimilation by growing cells of Ideonella sakaiensis.

A bacterium that degrades and assimilates poly(ethylene terephthalate).

Poly(ethylene terephthalate) (PET) is used extensively worldwide in plastic products, and its accumulation in the environment has become a global concern. Because the ability to enzymatically degrade PET has been thought to be limited to a few fungal species, biodegradation is not yet a viable remediation or recycling strategy. By screening natural microbial communities exposed to PET in the environment, we isolated a novel bacterium, Ideonella sakaiensis 201-F6, that is able to use PET as its major energy and carbon source. When grown on PET, this strain produces two enzymes capable of hydrolyzing PET and the reaction intermediate, mono(2-hydroxyethyl) terephthalic acid. Both enzymes are required to enzymatically convert PET efficiently into its two environmentally benign monomers, terephthalic acid and ethylene glycol.

Isothermal Crystallization Process of Poly(l-lactic acid)/Poly(d-lactic acid) Blends after Rapid Cooling from the Melt.

We observed the crystallization process in poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) blends using in situ simultaneous small- and wide-angle X-ray scattering measurements with a high-speed temperature control cell. In situ X-ray scattering measurements revealed that density fluctuations larger than the long spacing periods grew during crystallization above 130 °C. In particular, the time evolution of the density fluctuations has a strong dependence on the crystallization temperature. The density fluctuations will promote the crystal nucleation and growth processes of the stereocomplex and increase with increasing crystallization temperature, which is strongly correlated with the complexation of PLLA and PDLA chains. On the other hand, below 120 °C, the kinetics of stereocomplex formation might be hindered by the decreased mobility, and no density fluctuations were observed in the case of homo crystal growth of PLLA or PDLA.

Catalytic Generation of Oxalate through a Coupling Reaction of Two CO(2) Molecules Activated on [(Ir(eta(5)-C(5)Me(5)))(2)(Ir(eta(4)-C(5)Me(5))CH(2)CN)(&mgr;(3)-S)(2)].

Electrochemical reduction of [(Ir(eta(5)-C(5)Me(5)))(3)(&mgr;(3)-S)(2)](BPh(4))(2) ([Ir(3)S(2)](BPh(4))(2)) in CO(2)-saturated CH(3)CN at -1.30 V (vs Ag/AgCl) produced C(2)O(4)(2)(-) and [(Ir(eta(5)-C(5)Me(5)))(2)(Ir(eta(4)-C(5)Me(5))CH(2)CN)(&mgr;(3)-S)(2)](+) ([Ir(3)S(2)CH(2)CN](+)). The crystal structure of [Ir(3)S(2)CH(2)CN](BPh(4)) by X-ray analysis revealed that a linear CH(2)CN group is linked at the exo-position of a C(5)Me(5) ligand, and the C(5)Me(5)CH(2)CN ligand coordinates to an Ir atom with an eta(4)-mode. The cyclic voltammogram of [Ir(3)S(2)CH(2)CN](+) in CH(3)CN under CO(2) exhibited a strong catalytic current due to the reduction of CO(2), while that of [Ir(3)S(2)](2+) did not show an interaction with CO(2) in the same solvent. The reduced form of [Ir(3)S(2)CH(2)CN](+) works as the active species in the reduction of CO(2). The IR spectra of [Ir(3)S(2)CH(2)CN](+) in CD(3)CN showed a reversible adduct formation with CO(2) and also evidenced the oxalate generation through the reduced form of the CO(2) adduct under the controlled potential electrolysis of the solution at -1.55 V. A coupling reaction of two CO(2) molecules bonded on adjacent &mgr;(3)-S and Ir in [Ir(3)S(2)CH(2)CN](0) is proposed for the first catalytic generation of C(2)O(4)(2)(-) without accompanying CO evolution.