Genome shuffling and ribosome engineering of Streptomyces virginiae for improved virginiamycin production.

The production of virginiamycin (VGM) from Streptomyces virginiae was improved by genome shuffling and ribosome engineering companied with a high-throughput screening method integrating deep-well cultivation and the cylinder-plate detecting. First, a novel high-throughput method was developed to rapidly screen large numbers of VGM-producing mutants. Then, the starting population of genome shuffling was obtained through ultraviolet (UV) and microwave mutagenesis, and four mutants with higher productivity of VGM were selected for genome shuffling. Next, the parent protoplasts were inactivated by UV and heat when a fusant probability was about 98%. Streptomycin resistance was used as an evolutionary pressure to extend positive effects on VGM synthesis. Finally, after five rounds of genome shuffling, a genetically stable strain G5-103 was obtained and characterized to be able to yield 251 mg/L VGM, which was 3.1- and 11.6-fold higher than that of the mutant strain UV 1150 and the wild-type strain, respectively.

The effect of stachydrine on the expression of caspase-12 in rats with unilateral ureteral obstruction.

PURPOSE: We studied the effect of stachydrine on the expression of caspase-12 and 9 in rats with unilateral ureteral obstruction. MATERIALS AND METHODS: An animal model of renal interstitial fibrosis was established using unilateral ureteral obstruction with enalapril as the positive control. Rats were randomly divided into 6 groups, including sham treated, model, enalapril, and high, medium and low stachydrine. On day 14 postoperatively the rats were sacrificed. Serum was collected to determine serum creatinine and blood urea nitrogen. Tubular injury index was measured by hematoxylin and eosin staining. Renal interstitial collagen deposition was analyzed semiquantitatively by Masson staining. Expression of the apoptotic factors caspase-12 and 9 in renal tissues was determined by immunohistochemistry. RESULTS: The renal tubular interstitial damage index, degree of renal interstitial fibrosis, serum creatinine, blood urea nitrogen, and expression of caspase-12 and 9 in the treatment groups were significantly decreased compared to the model group (p <0.05 and <0.01, respectively). Serum creatinine, blood urea nitrogen, renal tubular injury, collagen deposition, and expression of caspase-12 and 9 in the high stachydrine group were significantly decreased compared with the enalapril group (p <0.05). CONCLUSIONS: Stachydrine interfered with the endoplasmic reticulum stress mediated apoptosis pathway by decreasing caspase-12 expression and inhibiting caspase-9 activation. Ultimately renal tubular epithelial cell apoptosis was suppressed and renal interstitial fibrosis development was postponed.

Effect of stachydrine on endoplasmic reticulum stress-induced apoptosis in rat kidney after unilateral ureteral obstruction.

Our study aimed at determining the effect of stachydrine on the PERK, CHOP, and caspase-3 in rat kidney with RIF. Rats were randomly divided into control group, model group, enalapril group, high stachydrine group, medium stachydrine group, and low stachydrine group. RIF models of five groups were developed by unilateral ureteral obstruction except the control group. The rats were sacrificed 12 days after surgery and blood samples were collected. Serum creatinine (Scr) and blood urea nitrogen (BUN) levels were detected. Renal tubular damage index was determined by HE staining. The area percentage of RIF was determined by the Masson method. Expressions of PERK, CHOP, and caspase-3 in kidney were determined by immunohistochemistry. Tubulointerstitial injury index, RIF, serum Scr, BUN level, and expressions of PERK, CHOP, and caspase-3 were different between the model and treatment groups (P < 0.05; P < 0.01). The expressions of PERK, CHOP, and caspase-3 in nephridial tissue were reduced (P < 0.05), tubulointerstitial injury and RIF were reduced (P < 0.05), and Scr and BUN were lower (P < 0.05) in the high stachydrine group than those in the enalapril group. The expressions of PERK, CHOP, and caspase-3 were reduced in the endoplasmic reticulum stress-related apoptosis pathway after stachydrine treatment. Consequently, apoptosis was prevented, and RIF was inhibited.

Development of a stepwise aeration control strategy for efficient docosahexaenoic acid production by Schizochytrium sp.

The effect of aeration on the performance of docosahexaenoic acid (DHA) production by Schizochytrium sp. was investigated in a 1,500-L bioreactor using fed-batch fermentation. Six parameters, including specific growth rate, specific glucose consumption rate, specific lipid accumulation rate, cell yield coefficient, lipid yield coefficient, and DHA yield coefficient, were used to understand the relationship between aeration and the fermentation characteristics. Based on the information obtained from the parameters, a stepwise aeration control strategy was proposed. The aeration rate was controlled at 0.4 volume of air per volume of liquid per minute (vvm) for the first 24 h, then shifted to 0.6 vvm until 96 h, and then switched back to 0.4 vvm until the end of the fermentation. High cell density (71 g/L), high lipid content (35.75 g/L), and high DHA percentage (48.95%) were achieved by using this strategy, and DHA productivity reached 119 mg/L h, which was 11.21% over the best results obtained by constant aeration rate.