Fig. 2: Bifidobacterium species produce aromatic lactic acids via an ALDH.
a, In vitro production of ILA, PLA and 4-OH-PLA by Bifidobacterium species type strains in modified MRS medium (MRSc) with 2% (w/v) glucose or a mix of HMOs as sole carbohydrate source. For the type strains of B. adolescentis, B. animalis ssp. animalis, B. animalis ssp. lactis, B. dentium and B. catenulatum, no or very poor growth (OD600nm < 0.4) was observed with HMOs as the carbohydrate source. Means of three biological replicates are shown. b, Neighbour-joining phylogenetic tree of all genes in the Bifidobacterium species type strains annotated as LDH-encoding genes (ldh). The four clusters are designated types 1–4. c, Production of ILA, PLA and 4-OH-PLA by E. coli LMG194 cells transformed with an inducible vector lacking (empty vector) or containing the type 4 ldh (Type4_ldh+) from B. longum ssp. infantis DSM 20088 in LB medium 5 h post-induction of gene expression by addition of l-arabinose and supplementation with the aromatic pyruvic acids (indolepyruvic acid, phenylpyruvic acid and 4-hydroxyphenylpyruvic acid). Bars show mean ± s.d. of three biological replicates. d, Growth curves of B. longum ssp. longum 105-A (WT), its isogenic insertional type 4 ldh mutant (Type4_ldh mutant) and the type 4 ldh mutant strain complemented with the type 4 ldh gene (complemented). Curves show mean ± s.d. of three biological replicates and doubling times reported as mean ± s.d.. e, Production of ILA, PLA, 4-OH-PLA and lactic acid by wild type, Type4_ldh mutant and the complemented strain in early stationary phase cultures as indicated in d. Bars show mean ± s.d. of three biological replicates. Statistical significance was evaluated by one-way ANOVA. ND, not detected.
