Synergism among lactic acid, sulfite, pH and ethanol in alcoholic fermentation of Saccharomyces cerevisiae (PE-2 and M-26)

Summary The industrial production of ethanol is affected mainly by contamination by lactic acid bacteria besides others factors that act synergistically like increased sulfite content, extremely low pH, high acidity, high alcoholic content, high temperature and osmotic pressure. In this research two strains of Saccharomyces cerevisiae PE-2 and M-26 were tested regarding the alcoholic fermentation potential in highly stressed conditions. These strains were subjected to values up to 200 mg NaHSO₃ l⁻¹, 6 g lactic acid l⁻¹, 9.5% (w/v) ethanol and pH 3.6 during fermentative processes. The low pH (3.6) was the major stressing factor on yeasts during the fermentation. The M-26 strain produced higher acidity than the other, with higher production of succinic acid, an important inhibitor of lactic bacteria. Both strains of yeasts showed similar performance during the fermentation, with no significant difference in cell viability.     

Comparison of pH and Bile Resistance of Lactobacillus acidophilus Strains Isolated from Rat, Pig, Chicken, and Human Sources

Summary To provide a useful screening method for selecting probiotics, we compared the pH and bile resistance of four strains of Lactobacillus acidophilus, KCTC3140, KCTC3146, KCTC3154, and KCTC3179, isolated from a rat, pig, chicken, and human, respectively. When we compared the pH resistance of these strains at pH 2, 3, 4, 5 and 7, we found that L. acidophilus isolated from the rat, chicken, and pig showed little or no decrease in viable cell numbers, except at 240 min, whereas the numbers of L. acidophilus KCTC3179 from the human decreased significantly. All four strains were slightly suppressed over time and showed bile resistance, even at 3%. At 5% oxgall, the number of KCTC3179 rapidly decreased at 30 min. These results indicate that lactic acid bacteria selected for probiotic use should be screened at pH 2 for 120 min and/or at an oxgall concentration of 5% for 30 min.     

Efficient production of ε-poly-l-lysine from glucose by two-stage fermentation using pH shock strategy

In this study, a pH shock strategy was employed to enhance ε-poly-l-lysine (ε-PL) production from glucose. In the conventional fermentation, in the early stage, only 13% of total ε-PL production is achieved in 25% of the entire fermentation period, which severely affected ε-PL productivity. To improve the efficiency of ε-PL production during fermentation, a novel two-stage fermentation, namely culture and fermentation stages, was proposed on the basis of the analysis of conventional pH shock fermentation. After optimization of parameters such as inoculum growth conditions, initial fermentation pH, and inoculum volume, the ε-PL production and productivity achieved using the novel fermentation process in a 5-L fermenter reached 32.22 g/L and 5.86 g/L/day, which were 32.3% and 36.6% higher, respectively, when compared with those obtained in conventional fermentation. Furthermore, evaluation of acid tolerance of mycelia collected from the pH shock fermentation showed that pH shock enhanced ε-PL production, which might be related to the acid tolerance of Streptomyces albulus and pH stress (pH 3.0). The results obtained could be useful for large-scale ε-PL production and to provide new information on ε-PL biosynthesis mechanism.     

“探究影响酶活性的条件”实验中的几项注意点

“探究影响酶活性的条件”是高中生物学课程中的一重要探究性实验,就如何使“探究温度对酶活性的影响”和“探究pH对酶活性的影响”的实验设计更科学、可行做了几点总结。     

Detection of ER stress in vivo by Raman spectroscopy

The endoplasmic reticulum (ER) is an organelle in which most membrane and secretory proteins are synthesized. If these proteins are not folded correctly, unfolded proteins accumulate in the ER lumen, causing a cellular situation known as ER stress. Recently, many studies on the relationship between ER stress and diseases have been reported. Thus, studies of ER stress in vivo should yield information that is useful in pathology. Model mice have been developed as a powerful tool to visualize ER stress in vivo, but this approach depends on transgenic technology. Here, we report on a method of detecting ER stress in vivo by Raman spectroscopy. Our experiments revealed that two specific Raman bands were reduced in both cultured cells and animal tissues in an ER stress dependent manner. This suggests that Raman spectroscopy could be a useful tool to detect ER stress in vivo without transgenic technology.     

The reduction of food web robustness by parasitism: fact and artefact

A robust food web is one which suffers few secondary extinctions after primary species losses. While recent research has shown that a food web with parasitism is less robust than one without, it still remains unclear whether the reduction in robustness is due to changes in network complexity or unique characteristics associated with parasitism. Here, using several published food webs, simulation experiments with different food web models and extinction scenarios were conducted to elucidate how such reduction can be achieved. Our results show that, regardless of changes in network complexity and preferential parasitism, the reduction in food web robustness is mainly due to the life cycle constraint of parasites. Our findings further demonstrate that parasites are prone to secondary extinctions and that their extinctions occur earlier than those involving free-living species. These findings suggest that the vulnerable nature of parasites to species loss makes them highly sensitive indicators of food web integrity.     

Enzymatic synthesis of dimeric glycomimetic ligands of NK cell activation receptors

This work reveals new structural relationships in the complex process of the interaction between activation receptors of natural killer cells (rat NKR-P1, human CD69) and novel bivalent carbohydrate glycomimetics. The length, glycosylation pattern and linker structure of receptor ligands were examined with respect to their ability to precipitate the receptor protein from solution, which simulates the in vivo process of receptor aggregation during NK cell activation. It was found that di-LacdiNAc triazole compounds show optimal performance, reaching up to 100% precipitation of the present protein receptors, and achieving high immunostimulatory activities without any tendency to trigger activation-induced apoptosis. In the synthesis of the compounds tested, two enzymatic approaches were applied. Whereas a β-N-acetylhexosaminidase could only glycosylate one of the two acceptor sites available with yields below 10%, the Y284L mutant of human placental β1,4-galactosyltransferase-1 worked as a perfect synthetic tool, accomplishing even quantitative glycosylation at both acceptor sites and with absolute regioselectivity for the C-4 position. This work insinuates new directions for further ligand structure optimisation and demonstrates the strong synthetic potential of the mutant human placental β1,4-galactosyltransferase-1 in the synthesis of multivalent glycomimetics and glycomaterials.