Purification and characterization of the low molecular weight xylanase from Bacillus cereus L-1.

Xylanase is widely used in various industries such as food processing, paper, textiles, and leather tanning. In this study, Bacillus cereus L-1 strain was isolated and identified as capable of producing low molecular weight xylanase through 16 s rRNA sequencing. Maximum xylanase yield of 15.51 ± 2.08 U/mL was achieved under optimal fermentation conditions (5% inoculum, 20 g/L xylan, pH 6.0, for 24 h). After purification via ammonium sulfate precipitation and High-S ion exchange chromatography, electrophoretic purity xylanase was obtained with a 28-fold purification and specific activity of 244.97 U/mg. Xylanase had an optimal pH of 6.5 and temperature of 60 °C and displayed thermostability at 30 °C and 40 °C with 48.56% and 45.97% remaining activity after 180 min, respectively. The xylanase retained more than 82.97% of its activity after incubation for 24 h at pH 5.0 and was sensitive to metal ions, especially Mg2+ and Li+. Purified xylanase showed a molecular weight of 23 kDa on SDS-PAGE, and partial peptide sequencing revealed homology to the endo-1,4-beta-xylanase with a molecular weight of 23.3 kDa through LC/MS-MS (liquid chromatography-tandem mass spectrometry). This study suggests that the purified xylanase is easier to purify and enriches low molecular weight xylanases from bacteria source.

Bitter and astringent substances in green tea: composition, human perception mechanisms, evaluation methods and factors influencing their formation.

Green tea is popularly known for its pleasant flavor and health-care functions. Bitterness and astringency are the two important quality attributes of green tea that enrich tea flavor. Although many research works have focused on the flavor formation of green tea, the review articles about bitterness and astringency is limited. This review article summarizes the major components of bitter and astringent substances in green tea, their sensory perception mechanism, factors influencing the formation of these substances, and the evaluation methods of bitterness and astringency. This review will shed light on the subsequent studies in tea flavor, and provide deeper insight for the research of bitterness and astringency in other foods.

NH4+ Toxicity, Which Is Mainly Determined by the High NH4+/K+ Ratio, Is Alleviated by CIPK23 in Arabidopsis.

Ammonium (NH4+) toxicity is always accompanied by ion imbalances, and NH4+ and potassium (K+) exhibit a competitive correlation in their uptake and transport processes. In Arabidopsis thaliana, the typical leaf chlorosis phenotype in the knockout mutant of calcineurin B-like interacting protein kinase 23 (CIPK23) is high-NH4+-dependent under low-K+ condition. However, the correlation of K+ and NH4+ in the occurrence of leaf chlorosis in the cipk23 mutant has not been deeply elucidated. Here, a modified hydroponic experimental system with different gradients of NH4+ and K+ was applied. Comparative treatments showed that NH4+ toxicity, which is triggered mainly by the high ratio of NH4+ to K+ (NH4+/K+ ≥ 10:1 for cipk23) but not by the absolute concentrations of the ions, results in leaf chlorosis. Under high NH4+/K+ ratios, CIPK23 is upregulated abundantly in leaves and roots, which efficiently reduces the leaf chlorosis by regulating the contents of NH4+ and K+ in plant shoots, while promoting the elongation of primary and lateral roots. Physiological data were obtained to further confirm the role CIPK23 in alleviating NH4+ toxicity. Taken all together, CIPK23 might function in different tissues to reduce stress-induced NH4+ toxicity associated with high NH4+/K+ ratios by regulating the NH4+-K+ balance in Arabidopsis.