Next generation sequencing based transcriptomic analysis of oxidative stress response in Bifidobacterium longum BBMN68

Bifidobacterium longum strain BBMN68 is resistant to low concentrations of oxygen. In this study, a transcriptomic study was performed to detail the cellular response of B. longum strain BBMN68 to oxidative stress. Oxygen and its intermediate metabolites, reactive oxygen species (ROS), induced abundant changes in gene expression at the mRNA level. Increased expression was found for genes involved in ROS detoxification and the redox homeostasis system, protein and DNA synthesis and repair, the Fe–S cluster assembly system, and biosynthesis of branched-chain amino acids and tetrahydrofolate. Among them, two classes of ribonucleotide reductase (RNR), which are important for deoxyribonucleotide biosynthesis, were rapidly and persistently induced: first, the class Ib RNR NrdHIEF and then the class III RNR NrdDG. The increased resistance to oxygen and hydrogen peroxide conferred by NADH oxidase was confirmed by its heterogeneous overexpression in B. longum strain NCC2705. In addition, cell-membrane and cell-wall compositions were modified, probably by an increase in cyclopropane fatty acids and a decrease in polysaccharides, respectively, resulting in improved cell hydrophobicity and autoaggregation; this subsequently reduced the permeation of dissolved oxygen into the cell. Taken together, the proposed cell model of B. longum responses to oxygen stress suggests that this bacterium employs a complex molecular defense mechanism against oxygen-induced stresses.