The commonness and difference among the Lactobacillus feruloyl esterases expressed in Escherichia coli

Background: Construction of recombinant Escherichia coli strains carrying feruloyl esterase genes for secretory expression offers an attractive way to facilitate enzyme purification and one-step produce ferulic acid from agricultural waste. It was found that the Lactobacillus crispatus feruloyl esterase could be secreted into extracellular environment of E. coli. Whether other Lactobacillus feruloyl esterases share the same secretory characteristic is worth investigation.Results: A total of ten feruloyl esterases derived from nine Lactobacillus species were used to analyze their commonness and compare their difference when heterologously expressed in E. coli BL21 (DE3). Extracellular activity determination showed all these Lactobacillus feruloyl esterases could be secreted out of E. coli cells. However, protein analysis indicated that they could be classified as three types. The first type presented a low secretion level, including feruloyl esterases derived from Lb. acidophilus and Lb. johnsonii. The second type showed a high secretion level, including feruloyl esterases derived from Lb. amylovorus, Lb. crispatus, Lb. gasseri and Lb. helveticus. The third type also behaved a high secretion level but easy degradation, including feruloyl esterases derived from Lb. farciminis, Lb. fermentum and Lb. reuteri. Moreover, these recombinant E. coli strains could directly release ferulic acid from de-starched wheat bran. Conclusions: Recombinant E. coli strains expressing feruloyl esterase of Lb. amylovorus, Lb. crispatus and Lb. helveticus displayed high secretion level and stable extracellular activity. Furthermore, the highest yield of ferulic acid was 140 µg on the basis of 0.1 g de-starched wheat bran after 72 h cultivation of E. coli expressing Lb. amylovorus feruloyl esterase. These results provided a solid basis for the production of feruloyl esterase and ferulic acid.