Yibo Zhu

Jiangnan University, Wuxi, Jiangsu Sheng, China

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Publications (5)10.92 Total impact

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    ABSTRACT: In the present study, we investigated the mode of cell response induced by D-limonene in Saccharomyces cerevisiae. D-limonene treatment was found to be accompanied by intracellular accumulation of reactive oxygen species (ROS). Since ROS impair cell membranes, an engineered strain with enhanced membrane biosynthesis exhibited a higher tolerance to D-limonene. Subsequent addition of an ROS scavenger significantly reduced the ROS level and alleviated cell growth inhibition. Thus, D-limonene-induced ROS accumulation plays an important role in cell death in S. cerevisiae. In D-limonene-treated S. cerevisiae strains, higher levels of antioxidants, antioxidant enzymes, and nicotinamide adenine dinucleotide phosphate (NADPH) were synthesized. Quantitative real-time PCR results also verified that D-limonene treatment triggered upregulation of genes involved in the antioxidant system and the regeneration of NADPH at the transcription level in S. cerevisiae. These data indicate that D-limonene treatment results in intracellular ROS accumulation, an important factor in cell death, and several antioxidant mechanisms in S. cerevisiae were enhanced in response to D-limonene treatment.
    Applied Microbiology and Biotechnology 05/2013; · 3.69 Impact Factor
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    ABSTRACT: AIMS: Enhancement of the tolerance of Saccharomyces cerevisiae to monoterpenes has the potential to improve the de novo biosynthesis of these chemicals as well as the efficient utilization of monoterpene-containing citrus waste. The aims of the current work are to demonstrate the mechanisms by which ergosterol, an important component of cell membranes, protects S. cerevisiae from D-limonene stress and to provide some useful information for further metabolic engineering of the yeast. METHODS AND RESULTS: S. cerevisiae cells were treated with a sub-lethal dose of D-limonene for 2 h, then ergosterol was added to investigate the physiological responses of S. cerevisiae. In D-limonene treated cells, the membrane fluidity, permeability and saturated fatty acid ratio increased, whereas the intracellular ergosterol concentration decreased sharply. Addition of ergosterol restored membrane and intracellular ergosterol to normal levels. Exogenous ergosterol triggered nearly all of the genes that encode the biosynthesis of ergosterol. CONCLUSIONS: In S. cerevisiae, the cell membrane is the target of D-limonene. Intracellular ergosterol availability is correlated with the D-limonene tolerance of the cells. IMPACT OF STUDY: The results indicate that modification of the ergosterol biosynthesis pathway could be a promising strategy for constructing a robust yeast strain with enhanced tolerance. © 2012 The Authors Journal of Applied Microbiology © 2012 The Society for Applied Microbiology.
    Journal of Applied Microbiology 10/2012; · 2.20 Impact Factor
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    ABSTRACT: Bacillus megaterium is widely used as companion bacterium in the two-step biosynthesis of 2-keto-l-gulonic acid (2-KLG) by Ketogulonicigenium vulgare. To screen efficiently target companion strains from large numbers of random mutants, a screen method based on spectrophotometry and 24-well microtiter plates was developed and validated on an integrated library of 450 transposon random insertional mutants and two sporulation-defective mutants. The co-culture processes were classified into three groups (low, intermediate and high performance) by K-mean clustering analysis. In addition, mutant m71 was successfully screened out from the library. The substrate conversion ratio of m71 and K. vulgare co-culture process after 72 h was decreased by about 38% compared with that of the wild-type co-culture process in 750 ml flasks. These results indicated that the proposed high throughput method is feasible for screening target companions for the co-culture process of 2-KLG biosynthesis.
    Process Biochemistry. 09/2012; 47(9):1428–1432.
  • Yibo Zhu, Jingwen Zhou, Jian Chen
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    ABSTRACT: Co-culturing Bacillus megaterium and Ketogulonigenium vulgare is widely applied to 2-keto-gulonic acid production. For optimizing the process, numerous researchers studied on the symbiotic molecular mechanism of the co-culture process. The research was promoted greatly owing to omics technologies, bioinformatics, high throughput technologies and physiology. Recently, the proteomic, metabolomic, comparative genomics and transcriptomics were performed to the research. These omics data provided us the interaction network of the artificial ecosystem in multilevel. Combining with the physiological validation based on the high throughput method, we can elucidate the molecular mechanism in detail, which will facilitate us to develop strategies for metabolic engineering. The paper reviewed the recent developments of symbiotic molecular mechanism research in this co-culture process and its applications. In addition, we proposed the future research needs.
    ACTA MICROBIOLOGICA SINICA 08/2012; 52(8):940-7.
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    ABSTRACT: Bacillus spp. is widely used as the companion bacterium in the two-step biosynthesis of 2-keto-L-gulonic acid (2-KLG), which is the direct precursor in the production of vitamin C by Ketogulonigenium vulgare. To understand the effects of sporulation and spore stability on 2-KLG production, the spo0A and spoVFA deletion mutants of Bacillus megaterium were constructed. The sorbose conversion rates of spo0A and spoVFA mutant co-culture systems were 33% and 70% lower, respectively, than that of the wild-type co-culture system. In addition, K. vulgare cell numbers in the two mutant systems declined by 15% and 49%, respectively, compared to the value in the wild-type system. Correlation analysis indicated that the 2-KLG concentration is positively related to sorbose dehydrogenase activity and the K. vulgare cell number. This study demonstrated that sporulation and spore stability of the wild-type companion play key roles in the enhancement of K. vulgare propagation and 2-KLG biosynthesis.
    Bioresource Technology 03/2012; 107:399-404. · 5.04 Impact Factor