Continuous, high level production and excretion of a plasmid-encoded protein by Escherichia coli in a two-stage chemostat

The stable continuous overproduction of a plasmidencoded protein, beta-lactamase, for at least 50 days by Escherichia coli K-12, RB791(pKN), with release into the culture medium has been demonstrated in two-stage chemostats. The second-stage culture was continuously induced with 0.1 mM IPTG. Continuous expression of beta-lactamase could not be sustained with this strain in a single-stage chemostat because of cell death and selection for lac(-1) cells. beta-Lactamase production in the second stage was sensitive to the second-stage dilution rate and the distribution of the limiting substrate (i.e., glucose) between the first and second stages. The fraction of viable, excreting cells and the average copy number in the induced culture was measurably higher under those conditions of dilution rate and substrate distribution which yielded high beta-lactamase levels. The best operating conditions found at 20 degrees C were a first-stage dilution rate of 0.12 h(-1), a second-stage dilution rate of 0.03 h(-1), and equal glucose feed supplied to each stage. Enzymatically active beta-lactamase was produced at a level of 25% of total cellular protein with 90% excretion yielding 300 mg beta-lactamase/L that was 50% pure at an OD(600) < 6. (c) 1993 Wiley & Sons, Inc.     

Localization of neuropeptide Y and atrial natriuretic peptide in the endothelial cells of human umibilical blood vessels

The localization of neuropeptide Y (NPY) and atrial natriuretic peptide (ANP) in the endothelial cells of human umbilical blood vessels was studied using the pre-embedding peroxidase-antiperoxidase (PAP) technique for electron microscopy and avidin-biotin-complex (ABC) immunostaining for endothelial cells cultured from umbilical vein. Subpopulations of NPY- and ANP-immunoreactive endothelial cells were present in term umbilical vein and artery. The umbilical vein contained more positive cells than the artery. The percentage of NPY- and ANP-immunoreactive umbilical vein cells in culture was 32% and 44%, respectively, out of a total of 3013 cells examined. The possibility that these potent vasoactive substances located in the endothelial cells of the non-innervated umbilical vessels are involved in the local regulation of blood flow is discussed.     

花生种子活力与贮藏蛋白质降解的关系

花生种子吸胀2d后,子叶中肽链内切酶活性上升,贮藏蛋白质开始降解。高活力种子肽链内切酶活性在吸胀2d后迅速上升,至4d时达到高峰,而中等活力种子的肽链内切酶活性上升速度绶慢。高活力种子萌发时贮藏蛋白质降解速度高于中等活力种子。中等活力种子经PEG和PUT处理可提高种子活力,也促进了种子贮藏蛋白质降解能力的提高。     

Growth kinetics for shelf-life prediction: Theory and practice

Summary Predictive microbiology can be used to determine and predict the shelf-life of perishable foods under commercial distribution conditions based on microbial growth kinetics. This paper presents general microbial growth kinetics with the Monod model and the Gompertz function. Additional models are given to describe effects of food composition (e. g.a _w) and environmental conditions (e.g. temperature, gas atmosphere) as well as their interaction on the growth kinetic parameters (lag time and specific growth rate). These models can be used to predict the time to reach a critical level under any constant conditions within the range tested. A combination of microbial kinetics with an engineering accumulation approach can be used to predict the final microbial level in a food, or the loss of shelf-life, for any known time-temperature sequence, if there is no history effect or the history effect is negligible. A time-temperature indicator, could be used for predicting the remaining shelf-life of perishable foods under any distribution condition based on microbial growth kinetics.Mention of brand or firm names does not constitute an endorsement by the US Department of Agriculture over others of a similar nature not mentioned.     

Scrapie I. Transmission and Pathogenesis

Homogenized brain, extracts, and residues of brain from normal and scrapie sheep were inoculated into 116 sheep. Of 72 sheep inoculated with scrapie material 27 developed the disease, whereas four of 44 inoculated with ;normal' brain material showed symptoms similar to those of scrapie. The scrapie agent survived extraction for 18 hours with diethyl ether followed by water for 24 hours. Similarly the agent survived extraction in a Soxhlet apparatus with 95 per cent ethanol containing 2.0 per cent 4 M HC1 for 24 hours. There was no evidence of demyelination in sections of brain and spinal cord supporting the view that allergic encephalomyelitis is not responsible for the scrapie symptoms. Liver function, as measured by the bromsulfalein test, remained normal until just before death. These results preclude that liver dysfunction contributes to the disease but do not exclude the possibilities of other metabolic derangements.