Present investigation explores the potential of defatted rice bran (DRB) serving as sole carbon source and partial nitrogen source to support Lactococcus lactis growth and nisin production. To retain the nutrients in DRB, especially protein fractions, thermal pretreatment followed by enzymatic hydrolysis without washing step was applied for saccharification. A maximum of 45.64g reducing sugar mainly containing 30.26g glucose and 5.66g xylose from 100g DRB was attained in hydrolysates of DRB (HD). A novel strategy of xylR (xylose transcriptional regulator) overexpression followed by evolutionary engineering was proposed, which significantly increased the capacity of L. lactis to metabolize xylose. Subsequently, RT-PCR results indicated that xylR overexpression stimulated expression of xylose assimilation genes synergistically with exposure to xylose. In HD medium, the highest nisin titer of the engineered strain FEXR was 3824.53IU/mL, which was 1.37 times of that in sucrose medium by the original strain F44.
Keywords: Defatted rice bran; Lactococcus lactis; Nisin; Xylose utilization; xylR.
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