YSI 2900 Aids Research Into E.coli Overflow Metabolism

YSI’s 2900 range of biochemical analysers is proving itself across a great range of applications and subject areas. The YSI 2900 model will measure two compatible chemistries and the YSI 2950 model up to six from a broad range of chemistries, including glucose, lactose, lactate, glutamate, glutamine, ammonium and ethanol.

The YSI 2900M Monitoring and Control system incorporates the Sitini Online Sampler to draw samples from a bioreactor automatically and deliver them to the 2900 for testing. Because of the speed and accuracy of analysis with the YSI 2900 investigations are now possible that would have proven difficult, if not impossible, using other measuring techniques. 

A case in point involves an investigation into Escherichia coli (E. coli) culturing. E. coli are important organisms that have been crucial to the development of the biotechnology industry as they can be used for producing a range of ‘products’, form biofuels to recombinant proteins. 
Excessive E, coli growth rates, however, can be self limiting by what is called ‘overflow metabolism’; acetate is excreted and this inhibits growth. By monitoring and limiting the addition of glucose to the culture medium or bioreactor, the E. Coli growth rate and hence the overflow metabolism, can be controlled. However, this and similar approaches can also result in reduced yield of recombinant protein and plasmid DNA per cell.
An approach has now been published which uses a different principle1; the idea being to increase the efficiency of aerobic metabolism. The technique is ingenious: respiratory activity was enhanced by aerobically expressing Vitreoscilla stercoraria haemoglobin (VHb), encoded with the gene vgh. The logic then is that VHb will increase the consumption of NADH in the respiratory chain, leading to increased activity of the tricarboxylic acid  (TCA) cycle. This should cause increased consumption of acetyl Co-A and hence a decrease in acetate production.
In order to analyse whether this did indeed occur the researchers turned to the YSI 2900 biochemical analyser. Two E. coli strains (W3110 and MG1655 ) were compared in batch mode using a low (7 g/L) glucose concentration. The best strain was also tested under high (45 g/L) glucose  concentration in order to achieve high cell densities in batch mode.
By using their VHb strategy the researchers found acetate production decreased by 50% in MG1655 and more than 90% in W3110. In neither case was growth rates or biomass yields effected. VHb expression in mutant strains with higher TCA activity and reduced acetate formation resulted in a significant increase in both growth and glucose consumption  rates, without increased acetate production.
Thanks in part to the efficiency of the YSI biochemical analyser it has now been shown that enhancing the efficiency of aerobic metabolism is a valuable approach to avoid overflow metabolism in E. coli. 
1.Reference: ‘Aerobic expression of Vitreoscilla hemoglobin efficiently reduces overflow metabolism in Escherichia coli’ (March 2014)

Date added: 2015-05-25 15:31:16