S29: Differential Response of Bifidobacterium animalis ssp. lactis Strains to Hydrogen Peroxide Stress

Consumer interest in probiotic foods containing bifidobacteria is increasing, but industry efforts to secure high cell viability in foods is undermined by the sensitivity of these anaerobes to oxidative stress during food production or storage. To address this limitation, we investigated transcriptional responses of two fully sequenced Bifidobacterium animalis ssp. lactis strains, BL04 and DSM10140, to hydrogen peroxide (H₂O₂) exposure. Although the genome sequences for these strains are virtually identical, they display different levels of intrinsic and inducible H₂O₂ resistance. For transcriptomics, late log phase cells were exposed to a sub-lethal H₂O₂ concentration for 5 or 60 min, then mRNA was isolated, converted to cDNA, and hybridized to an Affymetrix microarray. Data analysis by the limma/eBayes method found significant (P<0.05) changes in 158 genes in BL04 after 5 min, and 30 differentially expressed genes after 60 min. Surprisingly, no significant changes in gene expression were detected in DSM10140 at either time. Examination of genomic data for each strain suggested differences in H₂O₂ stress resistance might be related to membrane lipid composition, due to genetic mutations in genes for long chain fatty acid-coA ligase. To address this hypothesis, membrane fatty acids were isolated and analyzed by GC-MS.  Results confirmed the two strains had significantly different lipid profiles.  In particular, the BL04 membrane contained higher percentages of C14:0 and C16:0, and lower percentages of C16:1n7 and C18:1n9. These differences could affect membrane fluidity and, potentially, transduction of stress signals, either of which could explain the observed contrasts in H₂O₂ stress resistance.