Development of a novel expression system in lactic acid bacteria controlled by a broad-host-range promoter P <subscript>srfA</subscript> .

Background: Latic acid bacteria (LAB) are exploited for development of gene expression system owing to its health promoting properties and a high degree of safety status. Most of the expression systems were constructed in Lactobacillus lactis with inducible promoters. It is necessary to exploit novel promoters to develop LAB host platforms which are indispensable in dairy and health application to satisfy the production demand of increased number of target-genes. Previously, promoter P srfA had been displayed broad host range and used to construct auto-inducible expression system in B. subtilis and E. coli. In this work, the feasibility of P srfA in LAB was estimated.

Results: Plasmid with the green fluorescent protein (GFP) inserting downstream of P srfA was transformed into L. casei 5257, L. plantarum 97, L. fermentum 087 and Weissella confusa 10, respectively. The recombinant strains grew well and displayed different fluorescence which could be detected by spectrophotometer and laser scanning confocal microscope. Moreover, the promoter activity was strain- specifically influenced by particular carbon and nitrogen sources. Heterologous laccase CotA could be expressed by P srfA in L. casei 5257-05 and L. plantarum 97-06. By adjusting the pH value from 4.5 to 6.5 during incubation, the CotA activity detected from L. plantarum 97-05 and L. casei 5257-05 was increased by 137.7% and 61.5%, respectively. Finally, the fermentation pH was variably up-regulated along with the production of NADH oxidase which was controlled by the P srfA and its derivative mutated with core regions.

Conclusions: These data suggested that P srfA was valid for gene expression in different species of LAB. Moreover, P srfA could be used as an attractive candidate for fine-tuning gene expression in a broad range of prokaryotic expression plants.

(© 2022. The Author(s).)