Fig. 1

Screening of recombinant strains. a Verification of gene kerBp. Lane M, DNA marker; Lane 1–2, PCR amplification of kerBp. b Mg²⁺ concentration gradient. Lane M, DNA marker; lane 1–10, Mg²⁺: 1 mM, 2 Mm, 3 mM, 4 mM, 5 mM, 6 mM, 7 mM, 8 mM, 9 mM, 10 mM. c Mn²⁺ concentration gradient. Lane M, DNA marker; lane 1–5, Mn²⁺: 0.1 mM, 0.2 Mm, 0.3 mM, 0.4 mM, 0.5 mM. d Rescreening results of shake flasks. e SDS-PAGE analysis of WT and variant T18. Lane M, protein MW markers; lane 1, supernatant of fermentation broth from B. subtilis WB600 harboring pMA5 as the control; lane 2, WT; lane 3, variant T18