No abstract

Gluconobacter oxydans is well-known for its incomplete oxidizing capacity and has been widely applied in industrial production. However, genetic tools in G. oxydans are still scarce compared with model microorganisms, limiting its metabolic engineering. This study aimed to develop a clustered regularly interspaced short palindromic repeats interference (CRISPRi) system based on the typical type I-E endogenous CRISPR/CRISPR-associated proteins (Cas) system in G. oxydans WSH-003. The nuclease Cas3 in this system was inactivated naturally and hence did not need to be knocked out. Subsequently, the CRISPRi effect was verified by repressing the expression of fluorescent proteins, revealing effective multiplex gene repression. Finally, the endogenous CRISPRi system was used to study the role of the central carbon metabolism pathway, including the pentose phosphate pathway (PPP) and Entner–Doudoroff pathway (EDP), in G. oxydans WSH-003. This was done to demonstrate a metabolic engineering application. The PPP was found to be important for cell growth and the substrate conversion rate. The development of the CRISPRi system enriched the gene regulation tools in G. oxydans and promoted the metabolic engineering modification of G. oxydans to improve its performance. In addition, it might have implications for metabolic engineering modification of other genetically recalcitrant strains.

A sequential heuristic algorithm is presented for the one-dimensional cutting stock problem in which a set of items with specified length and demand are cut from the stock rods such that the waste is minimized. The algorithm generates a cutting pattern using items of a selected subset of the unassigned items, determines the frequency (number of times) at which the pattern can be used, deletes from the set of the unassigned items those that are assigned to the current pattern, and repeats until all items have been assigned. The selected subset is determined such that the frequency of the generated pattern can be as large as possible, provided that some constraints are observed to keep reasonable trim loss, and the cutting pattern is obtained from solving a bounded knapsack problem. The computational test on 18 classes of 1800 benchmark instances indicates that the algorithm performs better than two recently published algorithms for pattern reduction.

No abstract

Three crosslinked copolymer nanospheres were prepared by inverse microemulsion polymerization. Resistance temperature and resistance salinity of the copolymer CP(AM-AA-AMPS) [crosslinked poly(acrylamide-acrylic acid-2-acrylamide-2-methylacrylic sulfonic acid)] nano-spheres were superior to the CPAM (crosslinked polyacrylamide) nano-spheres and CP(AM-AA) [crosslinked poly(acrylamide-acrylic acid)] nano-spheres. The nanospheres had a tendency to plug the high-permeability layer and drive crude oil from the low-permeability layer. Meanwhile, these nanospheres displaced crude oil that existed in the pores or throats when they were conveyed in porous media. Consequently, deep profile control and oil displacement could be entirely actualized, and the ultimate goal of enhanced oil recovery could be achieved for high-temperature and high-salinity reservoirs.