Production of Recombinant Proteins in Bacillus subtilis

The classical way of protein purification starting from a large number of cells producing the protein using its authentic expression signals has been replaced by recombinant technology, where the protein of interest is overproduced in a regulated way. This often means that the recombinant gene is fused to a controllable promoter, which is activated by addition of an inducer to initiate transcription. In most cases, the inducer is a small molecule that is either taken up by the cells or diffuses through the cytoplasmic membrane such as isopropyl thiogalactose (IPTG), xylose, glycine. Overproduction of recombinant proteins is always a two-step process starting with a growth regimen to obtain a high cell density followed by the expression phase. First, cells are grown into the appropriate medium into the appropriate growth phase (with bacteria normally into the mid- or late-exponential growth phase) and then cells will be induced.