Enhanced l-Lysine into 1,5-Diaminopentane Conversion via Statistical Optimization of Whole-Cell Decarboxylation System.

The global lysine companies in the feed industry have steadily built their production facilities due to the high demand for l-lysine in animal farms, and in recent years there have been excessive supply problems and the world market price of l-lysine has fallen. In this study, the conversion of 1,5-diaminopentane (DAP) by decarboxylation of l-lysine was strategically chosen to enhance the value of lysine. The decarboxylation is enzymatically accessible, and Hafnia alvei, which is the producer of l-lysine decarboxylase, was applied as a whole-cell form. In the designed whole-cell biocatalytic system, the major four reaction factors were selected by fundamental investigation and then statistical optimization was performed to estimate the optimum condition. The predicted conversion was assessed at about 94.6% at the optimum conditions (125.1 mM l-lysine and 71.5 g/L acetone concentration at 35.2 °C for 8.4 h). Under the determined conditions, DAP conversions by using analytical, feed and industrial crude l-lysine were found to be 98.3%, 92.5% and 72.4%, respectively. These results could be suggested to solve the problem of excessive supplied lysine and also to provide guidance for improved enzymatic conversion by statistical optimization.

Toxic effects of individual and combined effects of BTEX on Euglena gracilis.

BTEX is a group of volatile organic compounds consisting of benzene, toluene, ethylbenzene and xylenes. Environmental contamination of BTEX can occur in the groundwater with their effects on the aquatic organisms and ecosystem being sparsely studied. The aim of this study was to evaluate the toxic effects of individual and mixed BTEX on Euglena gracilis (E. gracilis). We examined the growth rate, morphological changes and chlorophyll contents in E. gracilis Z and its mutant SMZ cells treated with single and mixture of BTEX. BTEX induced morphological change, formation of lipofuscin, and decreased chlorophyll content of E. gracilis Z in a dose response manner. The toxicity of individual BTEX on cell growth and chlorophyll inhibition is in the order of xylenes>ethylbenzene>toluene>benzene. SMZ was found more sensitive to BTEX than Z at much lower concentrations between 0.005 and 5 µM. The combined effect of mixed BTEX on chlorophyll contents was shown to be concentration addition (CA). Results from this study suggested that E. gracilis could be a suitable model for monitoring BTEX in the groundwater and predicting the combined effects on aqueous ecosystem.

Genotoxicity of hydroquinone in A549 cells.

Hydroquinone (HQ) is found in natural and anthropogenic sources including food, cosmetics, cigarette smoke, and industrial products. In addition to ingestion and dermal absorption, human exposure to HQ may also occur by inhaling cigarette smoke or polluted air. The adverse effects of HQ on respiratory systems have been studied, but genotoxicity HQ on human lung cells is unclear. The aim of this study was to investigate the cytotoxicity and genotoxicity of HQ in human lung alveolar epithelial cells (A549). We found that HQ induced a dose response in cell growth inhibition and DNA damage which was associated with an increase in oxidative stress. Cytotoxicity results demonstrated that HQ was most toxic after 24 h (LC50 = 33 µM) and less toxic after 1 h exposure (LC50 = 59 µM). Genotoxicity of HQ was measured using the Comet assay, H2AX phosphorylation, and chromosome aberration formation. Results from the comet assay revealed that DNA damage was highest during the earlier hours of exposure (1 and 6 h) and thereafter was reduced. A similar pattern was observed for H2AX phosphorylation suggesting that damage DNA may be repaired in later exposure hours. An increase in chromosomal aberration corresponded with maximal DNA damage which further confirmed the genotoxic effects of HQ. To investigate whether oxidative stress was involved in the cytotoxic and genotoxic effects of HQ, cellular glutathione and 8-Oxo-deoguanisone (8-Oxo-dG) formation were measured. A decrease in the reduced glutathione (GSH) and an increase oxidized glutathione (GSSG) was observed during the early hours of exposure which corresponded with elevated 8-Oxo-dG adducts. Together these results demonstrate that HQ exerts its cytotoxic and genotoxic effects in A549 lung cells, probably through DNA damage via oxidative stress.

Altered expression of genes related to zinc homeostasis in early mouse embryos exposed to di-2-ethylhexyl phthalate.

Numerous studies have shown that di-2-ethylhexyl phthalate (DEHP) is teratogenic in animals but the mechanism of developmental toxicity is not well understood. One hypothesis is altered zinc homeostasis. The present study has investigated the effect of DEHP exposure on several key genes in zinc metabolism (MT-I, MT-II, ZnT-1) for early mouse embryos exposed in utero. Time- and dose-dependent effects were examined using expression polymerase chain reaction (PCR) (relative to ACTB) and Western blot analysis of the maternal liver, embryonic brain, and visceral yolk sac at 9 days post-coitus (d.p.c.). Maternal exposure to 800 mg/kg DEHP increased the abundance of MT-I and MT-II transcripts in maternal liver at 3.0, 4.5 and 6.0 h after administration. MT-I and MT-II protein induction was confirmed by Western blot analysis. On the other hand, this exposure down-regulated both transcripts (MT-I, MT-II), as well as transcripts for a zinc transporter (ZnT-1), in the embryonic brain, but not the visceral yolk sac. To examine dose-response relationships, the experiment was repeated for DEHP exposures of 50, 200 and 800 mg/kg. The effect to MT-I and MT-II expression in the maternal liver became significant at the 200 mg/kg dose level. The contrasting effect to MT-I, MT-II and ZnT-1 expression in the embryo was also dose-dependent, and a benchmark computation for the dose resulting in a 5% change in the mean (BMD5) was estimated as 11.6 mg/kg for MT-I, 8.9 mg/kg for MT-II, and 6.6 mg/kg for ZnT-1. We conclude that DEHP exposure to pregnant dams at reasonably low levels during organogenesis stages can alter the expression of several key genes in embryonic zinc homeostasis.