Computational Analysis and Heterologous Expression of BBI-like Proteins from Food-Grade Bifidobacterium Species Reveal Possibly a Key Factor in Conjugated Linoleic Acid Bioconversion

Bifidobacteria are well-known probiotics that can produce multiple health-promoting bioactivities, including the bioconversion of conjugated linoleic acid (CLA). However, there is a lack of insights into the genetic diversity of functional proteins in Bifidobacterium at the species level, particularly owing to the vastly different CLA conversion capabilities of these strains. Here, we performed a comprehensive bioinformatics analysis and the in vitro expression of bbi-like sequences that are widely distributed among CLA-producing Bifidobacterium strains. The BBI-like protein sequences from all four species of bifidobacterial CLA-producing strains were predicted to be stable integral membrane proteins with a transmembrane topology number of seven or nine. All BBI-like proteins were found to be expressed in the Escherichia coli BL21(DE3) hosts with a pure c9, t11-CLA-producing activity. Furthermore, their activities significantly differed in the same genetic background, and their sequence differences were indicated to be important potential factors contributing to the high activity levels in CLA-producing Bifidobacterium breve strains. The use of microorganisms, such as food-grade or industrial-grade strains, to obtain single CLA isomers will accelerate CLA-related food and nutrition research and further enrich the scientific theory of bifidobacteria as probiotics.