Transcriptome analysis of Pichia pastoris in response to ethanol stress / 生物工程学报

Effective expression of pIFN-α in recombinant Pichia pastoris was conducted in a 5 L fermentor. Ethanol accumulation during the late glycerol feeding period inhibited heterologous protein expression. Comparative transcriptome analysis was thus performed to compare the gene transcription profiles of Pichia pastoris KM71H in high and low ethanol concentration environments. The results showed that during the glycerol cultivation stage, 545 genes (265 up-regulated and 280 down-regulated) were differentially expressed with ethanol stress. These genes were mainly involved in protein synthesis, energy metabolism, cell cycle and peroxisome metabolism. During the methanol induction stage, 294 genes (171 up-regulated and 123 down-regulated) were differentially expressed, which were mainly related to methanol metabolism, amino acid metabolism and protein synthesis. Ethanol stress increased protein misfolding and reduced structural integrity of ribosome and mitochondria during cultivation stage, and led to the failure of endoplasmic reticulum stress removal and damaged amino acid metabolism during induction stage in Pichia pastoris.

Enhanced production of curdlan by Alcaligenes faecalis by selective feeding with ammonia water during the cell growth phase of fermentation / 生物工程学报

Curdlan is a water insoluble exopolysaccharide produced by Alcaligenes faecalis under nitrogen-limiting conditions. After excretion, the polysaccharide is attached the cell wall. Thus enhancement of biomass production during the cell growth phase is important to curdlan production. A strategy of increasing nitrogen source to improve biomass production was adopted for curdlan production by Alcaligenes faecalis (ATCC 31749). In the batch fermentation of curdlan, a relatively higher NH4Cl level of 3.6 g/L with continuous glucose feeding increased the cell density leading to improvement of curdlan production. However, excessive NH4Cl would inhibit curdlan production and biomass production was not improved significantly. In addition, feeding of ammonia water at the initial phase replaced NaOH solution to control pH at 7.0. Subsequently, feeding of NaOH solution was resumed to control pH at 5.6 for curdlan production after ammonia was consumed. As a result, biomass production and curdlan yield were both enhanced remarkably. Feeding of ammonia water during the first 24 h led to biomass production of 18.8 g/L. However, higher cell density did not lead to increase in curdlan production. The maximum curdlan production (72 g/L) was obtained by feeding ammonia water for the first 14 h, during which the cell density was about 11.9 g/L.