To accomplish this we tested a selection of yeast extracts and peptones both separately and in combination, for growth and expression of two E. coli model-strains. That there is some merit in testing ingredients separately is demonstrated in an experiment where combining the least performing peptone and yeast extract also resulted in the lowest expression level.
However, this is not always the case and potentially great combinations can be overlooked as demonstrated by the example of N-Z-SoyTMBL4. In both model systems this non-animal peptone was one of the least performing products for growth and expression, if tested as the sole source of nitrogen. However, in combination with the right yeast extract it actually became one of the best performing nitrogen sources.
By screening combinations of peptones and yeast extracts, both for growth and expression in two different model-systems, we were able to formulate our new HyExpressTM line of non-animal nitrogen sources that have a very high probability of working for various E. coli based expression systems.