Utilizing a highly responsive gene, yhjX, in E. coli based production of 1,4-butanediol

The role of yhjX, a predicted major facilitator superfamily protein, was examined in context of E. coli response to 1,4-butanediol (1,4-BDO). E. coli DH1 and MG1655, two commonly used metabolic engineering hosts, were both sensitive to the presence of 1,4-BDO in the growth medium, but to different extents. The strains also showed differences in the transcriptional response of the yhjX gene that was highly induced in response to 1,4-BDO. yhjX deletion improved growth of the E. coli strains in the control defined medium but did not significantly impact 1,4-BDO sensitivity. Overexpression of yhjX using a plasmid-borne copy and lactose-inducible promoter also did not result in an improvement in 1,4-BDO tolerance. However, the large differential expression of yhjX in response to this diol provided the foundation to develop a biosensor for the detection of 1,4-BDO using a fluorescent gene under the control of the yhjX promoter. A basic PyhjX:GFP biosensor in E. coli DH1 allows the detection of 4-7% 1,4-BDO in the extracellular medium and provides a tool for high throughput engineering for improving 1,4-BDO production strains.