Derivative of the K12 strain with additional defects in the expression of recA and endAI. The recA mutation leads to the inability to homologously recombine DNA, resulting in the stabilisation of transferred recombinant plasmids. The endAI mutation considerably reduces endonuclease I activity, facilitating the isolation of DNA from cells.

The gene arsR including its promoter was transferred to the DH5α strain. The gene stems from the E. coli-specific plasmid R773 and encodes for a transcriptional regulator with binding sites for arsenic compounds. Furthermore, reporter genes were inserted into the recipient organisms using a vector. These are the luxCDABE genes required for the expression of luciferase from Photorhabdus luminescens.

This system employs the pSB403-arsR plasmid in the test bacteria. The vector background of this plasmid is the pRK415 plasmid, which is in turn derived from the RK2 plasmid from Klebsiella aerogenes. It contains an oriV, which enables a broad host range replication in Gram-negative bacteria, an oriT to start the plasmid transfer during a triparental conjugation and a tetracycline-resistance gene cartridge. The luxCDABE genes were inserted into pRK415 and the resulting plasmid was named pSB403. The expression of luxCDABE genes leads to emission of light.