Suchergebnisse

Clostridium tyrobutyricum (C. tyrobutyricum) is a fermentation strain used to produce butyric acid. A promising new biofuel, n-butanol, can be produced by catalysis of butyrate, which can be obtained through microbial fermentation. Butyric acid has various uses in food additives and flavor agents, antiseptic substances, drug formulations, and fragrances. Its use as a food flavoring has been approved by the European Union, and it has therefore been listed on the EU Lists of Flavorings. As butyric acid fermentation is a cost-efficient process, butyric acid is an attractive feedstock for various biofuels and food commercialization products. (12)C(6+) irradiation has advantages over conventional mutation methods for fermentation production due to its dosage conformity and excellent biological availability. Nevertheless, the effects of these heavy-ion irradiations on the specific productiveness of C. tyrobutyricum are still uncertain. We developed non-structured mathematical models to represent the heavy-ion irradiation of C. tyrobutyricum in biofermentation reactors. The kinetic models reflect various fermentation features of the mutants, including the mutant strain growth model, butyric acid formation model, and medium consumption model. The models were constructed based on the Markov chain Monte Carlo model and logistic regression. Models were verified using experimental data in response to different initial glucose concentrations (0–180 g/L). The parameters of fixed proposals are applied in the various fermentation stages. Predictions of these models were in accordance well with the results of fermentation assays. The maximum butyric acid production was 56.3 g/L. Our study provides reliable information for increasing butyric acid production and for evaluating the feasibility of using mutant strains of C. tyrobutyricum at the pre-development phase.

The crystal structures and properties of boron-silicon (B-Si) compounds under pressure have been systematically explored using particle swarm optimization structure prediction method in combination with first-principles calculations. Three new stoichiometries, B2Si, BSi, and BSi2, are predicted to be stable gradually under pressure, where increasing pressure favors the formation of silicon rich B-Si compounds. In the boron-rich compounds, the network of boron atoms changes from B12 icosahedron in the ambient phases to the similar buckled graphenelike layers in the high-pressure phases, which crystalize in the same P¯3m1 symmetry but with different numbers of boron layers between adjacent silicon layers. Phonon calculations show that these structures might be retained to ambient conditions as metastable phases. Further electron-phonon coupling calculations indicate that the high-pressure phases of boron-rich compounds might superconduct at 1 atm, with the highest Tc value of 21 K from the Allen-Dynes equation in P¯3m1 B2Si, which is much higher than the one observed in boron doped diamond-type silicon. Moreover, further fully anisotropic Migdal-Eliashberg calculations indicate that B2Si is a two-gap anisotropic superconductor and the estimated Tc might reach up to 30 K at 1 atm. On the silicon-rich side, BSi2 is predicted to be stable in the CuAl2-type structure. Our current results significantly enrich the phase diagram of the B-Si system and will stimulate further experimental study. ; The work was supported by Fostering Program of Major Research Plan of NSFC (91963115), National Key R & D Program of China (2018YFA0703400), National Natural Science Foundation of China (No. 51732010, 11674176, 11874224), Funding Program for Recruited Oversea Scholars of Hebei Province (Grant No. CL201729), and the Ph.D. Foundation by Yanshan University (Grant No. B970). A.B. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (Grant No. FIS2016-76617-P) and the Department of Education, Universities and Research of the Basque Government and the University of the Basque Country (Grant No. IT756-13). ; Peer reviewed