Enhancement of ε-poly-lysine production in ε-poly-lysine-tolerant Streptomyces sp. by genome shuffling.

ε-Poly-L-lysine (ε-PL) has been widely used as food additive. However, the self-inhibition of ε-PL on cell growth limits the accumulation of ε-PL in the wild-type strain. Here, we screened ε-PL-tolerant strain of Streptomyces sp. with higher ε-PL productivity by genome shuffling and studied the mechanism for the improvement. The initial mutant library was constructed by diethyl sulfate mutagenesis. After four rounds of protoplast fusion, a shuffled strain F4-22 with 3.11 g/L ε-PL productivity in shake flask, 1.81-fold in comparison with that of parent strain, was obtained. The higher aspartokinase activity was induced in F4-22 whereas no obvious changes have been found in ε-PL synthetic and degrading enzymes which indicated that the upstream reregulation of the precursor lysine synthesis rather than lysine polymerization or ε-PL degradation in shuffled strain accounted for the higher productivity. The activities of key enzymes in the central metabolic pathway were also enhanced in F4-22 which resulted in increased vigor of the strain and in delayed strain lysis during fermentation. These improved properties of shuffled strain led to the success of combining general two-stage fermentation into one-stage one in 5-L bioreactor with 32.7 % more ε-PL production than that of parent strain. The strategy used in this study provided a novel strain breeding approach of producers which suffered from ε-PL-like self-inhibition of the metabolites.

Endophytic Fungi Volatile Organic Compounds as Crucial Biocontrol Agents Used for Controlling Fruit and Vegetable Postharvest Diseases.

Fruits and vegetables are an important part of the human diet, but during transportation and storage, microbial pathogens attack and spoil fruits and vegetables, causing huge economic losses to agriculture. Traditionally used chemical fungicides leave chemical residues, leading to environmental pollution and health risks. With the emphasis on food safety, biocontrol agents are attracting more and more attention due to their environmental friendliness. Endophytic fungi are present in plant tissues and do not cause host disease. The volatile organic compounds (VOCs) they produce are used to control postharvest diseases due to their significant antifungal activity, as well as their volatility, safety and environmental protection characteristics. This review provides the concept and characterization of endophytic fungal VOCs, concludes the types of endophytic fungi that release antifungal VOCs and their biological control mechanisms, as well as focuses on the practical applications and the challenges of applying VOCs as fumigants. Endophytic fungal VOCs can be used as emerging biocontrol resources to control postharvest diseases that affect fruits and vegetables.

Pathogenic factors of cognitive dysfunction after liver transplantation: an observational study.

OBJECTIVES: Neurocognitive complications significantly reduce long-term health-related quality of life in patients undergoing liver transplantation; however, few studies have focused on their perioperative cognitive status. The authors designed a prospective observational study to determine the incidence and risk factors of posttransplant cognitive dysfunction. METHODS: This study included patients with end-stage liver disease who were on the liver transplantation waiting list. We performed an investigation with a neuropsychological battery before and 1 week after the successful transplant, analyzed the changes, and further explored the complicated perioperative factors that contribute to cognitive dysfunction. RESULTS: A total of 132 patients completed all the investigations. Compared with healthy controls and preoperative cognitive performance, 54 patients experienced deterioration, 50 patients remained unchanged, and 28 patients showed rapid improvement. Logistic regression analysis showed that age [odds ratio (OR) = 1.15, 95% confidence interval (CI, 1.07-1.22), P  < 0.001], the model for end-stage liver disease (MELD) score [OR = 1.07, 95% CI (1.03-1.13), P  = 0.038], systemic circulation pressure [OR = 0.95, 95% CI (0.91-0.99), P  = 0.026] within the first 30 min after portal vein opening, and total bilirubin concentration [OR = 1.02, 95% CI (1.01-1.03), P  = 0.036] on the seventh day post-transplant were closely related to the deterioration of cognitive function. CONCLUSION: The incidences of deterioration, maintenance, and improvement in cognitive function were 40.9%, 37.9%, and 21.2%, respectively. Increasing age, higher MELD score, lower perfusion pressure in the early stage of the new liver, and higher total bilirubin concentration postoperatively may be independent pathogenic factors.