Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, India.
Appl Microbiol Biotechnol. 2012 Mar;93(6):2543-9. doi: 10.1007/s00253-011-3642-3. Epub 2011 Oct 27.
Expression of proteins unneeded for growth diverts cellular resources from making necessary protein and leads to a reduction in the growth rate of an organism. This reduction in growth rate is termed as cost. Cost plays an important role in determining the selected expression of a protein in a particular environment. Characterization of cost is important in biotechnology industries where microorganisms are used to produce foreign proteins. We have used the lactose system in Escherichia coli to quantify the cost of growth on glycerol in the presence of isopropyl-β-D-thiogalactopyranoside (IPTG), an inducer of the lactose system. The effect of the concentration of the carbon source, glycerol, and the inducer of Lac enzymes, IPTG, is studied. The results show that the cost is dependent on the glycerol concentration with a decreasing trend with increasing concentration of glycerol. Also as expected, the cost increases and saturates at a higher concentration of IPTG. The studies also demonstrate that the cost is higher in early exponential phase relative to late exponential phase during the growth as has been reported in the literature. Hill equation fit yielded a typical Monod-type expression for growth on glycerol with and without IPTG. An apparent half-saturation constant was defined which was used to characterize the burden on growth due to protein expression.
表达不需要生长的蛋白质会使细胞资源从制造必需蛋白质中转移出来，导致生物体的生长速度减慢。这种生长速度的降低称为代价。代价在决定特定环境中蛋白质的选择表达方面起着重要作用。在生物技术行业中，微生物被用来生产外源蛋白质，因此对代价的特征进行研究非常重要。我们使用大肠杆菌的乳糖系统来量化在异丙基-β-D-硫代半乳糖苷（IPTG）存在下生长在甘油上的代价，IPTG 是乳糖系统的诱导物。研究了碳源甘油和 Lac 酶诱导物 IPTG 的浓度的影响。结果表明，代价与甘油浓度有关，随着甘油浓度的增加而呈下降趋势。正如预期的那样，代价随着 IPTG 浓度的增加而增加并达到饱和。研究还表明，正如文献中报道的那样，在生长过程中，与晚期指数期相比，早期指数期的代价更高。Hill 方程拟合对有和没有 IPTG 时甘油上的生长产生了典型的 Monod 型表达。定义了一个表观半饱和常数，用于描述由于蛋白质表达对生长的负担。
