Positively regulated bacterial expression systems

Abstract

SummaryRegulated promoters are useful tools for many aspects related to recombinant gene expression in bacteria, including for high‐level expression of heterologous proteins and for expression at physiological levels in metabolic engineering applications. In general, it is common to express the genes of interest from an inducible promoter controlled either by a positive regulator or by a repressor protein. In this review, we discuss established and potentially useful positively regulated bacterial promoter systems, with a particular emphasis on those that are controlled by the AraC‐XylS family of transcriptional activators. The systems function in a wide range of microorganisms, including enterobacteria, soil bacteria, lactic bacteria and streptomycetes. The available systems that have been applied to express heterologous genes are regulated either by sugars (l‐arabinose, l‐rhamnose, xylose and sucrose), substituted benzenes, cyclohexanone‐related compounds, ε‐caprolactam, propionate, thiostrepton, alkanes or peptides. It is of applied interest that some of the inducers require the presence of transport systems, some are more prone than others to become metabolized by the host and some have been applied mainly in one or a limited number of species. Based on bioinformatics analyses, the AraC‐XylS family of regulators contains a large number of different members (currently over 300), but only a small fraction of these, the XylS/Pm, AraC/PBAD, RhaR‐RhaS/rhaBAD, NitR/PnitA and ChnR/Pb regulator/promoter systems, have so far been explored for biotechnological applications.

Regulation of the rhaEWRBMA Operon Involved in l -Rhamnose Catabolism through Two Transcriptional Factors, RhaR and CcpA, in Bacillus subtilis

“…Moreover, in E. coli, the regulatory system of the rhaB promoter comprising RhaS, RhaR, and CRP is applied to the heterologous expression system, in which the expression of the target gene situated downstream of the rhaB promoter is capable of being strictly controlled by the addition of rhamnose or glucose (53). Similarly to this, it is possible that, in the cells of B. subtilis and related species, the expression of the introduced gene under the control of the rhaEW promoter can be finely regulated by RhaR and CcpA in the presence of rhamnose or glucose.…”

Modular system for assessment of glycosyl hydrolase secretion in Geobacillus thermoglucosidasius

“…Furthermore, the extent of expression from the lactate dehydrogenase (ldhA) promoter used in these examples is influenced by the redox conditions associated with the transition from aerobic to anaerobic growth, which may not be universally useful (Bartosiak-Jentys et al, 2012). Positively regulated protein expression systems in bacteria are common and rely on gene expression controlled by inducible promoters (Brautaset et al, 2009). Such promoters give tractable expression when induced with specific agents or conditions (e.g.…”

Mining Environmental Plasmids for Synthetic Biology Parts and Devices

“…The bottom line is that in the very competitive environments where these bacteria thrive, expression of extra genes must be tightly controlled for being triggered only when and where they are needed. This scenario is thus an excellent ground in which to mine pairs of transcriptional factors (TFs)/cognate chemical inducers which can be reformatted for creating new conditional expression systems (98). This approach is helping to overcome the dearth of alternative inducible devices for synthetic biology circuits (Fig.…”