Optimizational production of phenyllactic acid by a Lactobacillus buchneri strain via uniform design with overlay sampling methodology

A Lactobacillus buchneri GBS3 strain isolated from the traditional Chinese pickles was used for the production of 3-phenyllactic acid(PLA), an important compound with antimicrobial activities against a wide species of grampositive and gram-negative bacteria and some fungi. The growth performance of this strain in the de Man, Rogosa and Sharpe(MRS) medium, the production of metabolites of valuable organic acids, and the biosynthesis of PLA using this strain as the whole-cell biocatalyst and phenylpyruvic acid(PPA) as the precursor, were investigated experimentally. The uniform design method with overlay sampling was developed for the optimization of the biotransformation conditions. The results showed that although it produced naturally lactic acid with the maximum concentration of 1.84 g·L^(-1) and PLA with the concentration of 0.015 g·L^(-1) after 66 to 72 h cultivation in MRS broth by fermentation, the present strain displayed an effective utilization ability by transforming PPA to PLA. By the uniform design method with overlay sampling for the design and optimization of transformation conditions, a maximum yield of 10.93 g·L^(-1) PLA with the mole conversion ratio of 83.07% from PPA to PLA was achieved under the optimized condition, i.e., 20 g·L^(-1) glucose, 270 g·L^(-1) cells, 13 g·L^(-1) PPA, pH 8.0 and the reaction time of 15 h, indicating that Lactobacillus buchneri GBS3 was an interesting strain for the biosynthesis of PLA via the microbial transformation. The prediction of PLA yield under different conditions was achieved successfully based on the limited information of only a small number of experiments by the uniform design with overlay sampling. Therefore, the present methodology is effective and helpful for the optimization of the biosynthesis processes of PLA.

Photoinhibition of Leaves with Different Photosynthetic Carbon Assimilation Characteristics in Maize (<i>Zea mays</i>)

Strong light decreases the rate of photosynthesis and assimilates production of crop plants. Plants with different carbon reduction cycles respond differently to strong light stress. However, variation in photoinhibition in leaves with different photosynthetic characteristics in maize is not clear. In this experiment, we used the first leaves (with an incomplete C4 cycle) and fifth leaves (with a complete C4 cycle) of maize plants as well as the fifth leaves (C3 cycle) of tobacco plants as a reference to measure the photosynthetic rate (PN) and chlorophyll a parameters under strong light stress. During treatment, PN, the maximal fluorescence (Fm), the maximal quantum yield of PSII photochemistry (Fv/Fm), and the number of active photosystem II (PSII) reaction centers per excited cross-section (RC/CSm) declined dramatically in all three types of leaves but to different degrees. PN, Fm, Fv/Fm, and RC/CSm were less inhibited by strong light in C4 leaves. The results showed that maize C4 leaves with higher rates of photosynthesis are more tolerant to strong light stress than incomplete C4 leaves, and the carbon reduction cycle is more important to photoprotection in C4 leaves, while state transition is critical in incomplete C4 leaves.

Different Effects of Malate on the Activities of Photosystem II in Detached Leaves of Maize and Tobacco

Malate is the first stable product after CO2 is fixed in NADP-dependent malic enzyme (NADP-ME) type of C4 plants, which transfers CO2 and the reducing equivalent from mesophyll cell (MC) to vascular bundle sheath cell (BSC) chloroplasts and affects the redox state of BSC. The aim of this experiment is to investigate the effect of exogenous malate on the activity of photosystem II (PS II) in C4 and C3 plants. The leaf discs from the 5th fully expanded leaves of maize (NADP-ME type C4 plants) and the 10th fully expanded leaves of tobacco (C3 plants) were treated with malate of 50, 100 μM and the chlorophyll fluorescence parameters were measured. Malate treatments decreased the photochemical reaction efficiency (FV/FM) in maize leaves, as a result of rising in initial fluorescence (FO) and decreasing in maximal fluorescence (FM). The number of active PS II reaction center (RC) per excited cross section (RC/CS) declined in malate-treated maize, suggesting that malate inactivated PS II RC. Malate treatments also increased Wk, representing the severity of oxygen-evolving complex (OEC) damage, and decreased the rate of photosynthetic oxygen evolution. We conclude that exogenous malate regulates the activity and structure of PS II in C4 plant maize. No significant changes in the activity of PS II were observed in malate-treated C3 plant tobacco. It is suggested that the short term malate treatment will inhibit PS II of leaves which have C4 anatomy and C4 enzymes.

Bi-/multi-modal pore formation of PLGA/hydroxyapatite composite scaffolds by heterogeneous nucleation in supercritical CO_2 foaming

Scaffolds with multimodal pore structure are essential to cells differentiation and proliferation in bone tissue engineering. Bi-/multi-modal porous PLGA/hydroxyapatite composite scaffolds were prepared by supercritical C02 foaming in which hydroxyapatite acted as heterogeneous nucleation agent. Bimodal porous scaffolds were prepared under certain conditions, i.e. hydroxyapatite addition of 5%, depressurization rate of 0.3 MPa. min-1, soaking temperature of 55 ℃, and pressure of 9 MPa. And scaffolds presented specific structure of small pores （122 μM ± 66 μm） in the cellular walls of large pores （552 μm ±127 μm）. Furthermore, multimodal porous PLGA scaffolds with micro-pores （37 μM ± 11μM） were obtained at low soaking pressure of 7.5 MPa. The interconnected porosity of scaffolds ranged from （52.53 ± 2.69）% to （83.08±2.42）% by adjusting depressurization rate, while compression modulus satisfied the requirement of bone tissue engineering. Solvent-free CO2 foaming method is promising to fabricate bi-/multi-modal porous scaffolds in one step, and bioactive particles for osteogenesis could serve as nucleation agents.