Abstract
Bifidobacterium longum strain BBMN68 is sensitive to low concentrations of oxygen. A transcriptomic study was performed to identify candidate genes for B. longum BBMN68’s response to oxygen treatment (3%, v/v). Expression of genes and pathways of B. longum BBMN68 involved in nucleotide metabolism, amino acid transport, protein turnover and chaperones increased, and that of carbohydrate metabolism, translation and biogenesis decreased to adapt to the oxidative stress. Notably, expression of two classes of ribonucleotide reductase (RNR), which are important for deoxyribonucleotide biosynthesis, was rapidly and persistently induced. First, the class Ib RNR NrdHIEF was immediately upregulated after 5 min oxygen exposure, followed by the class III RNR NrdDG, which was upregulated after 20 min of exposure. The upregulated expression of branched-chain amino acids and tetrahydrofolate biosynthesis-related genes occurred in bifidobacteria in response to oxidative stress. These change toward to compensate for DNA and protein damaged by reactive oxygen species (ROS). In addition, oxidative stress resulted in improved B. longum BBMN68 cell hydrophobicity and autoaggregation. These results provide a rich resource for our understanding of the response mechanisms to oxidative stress in bifidobacteria.
Highlights
Enzymes such as NADH oxidase, NADH peroxidase, catalase and superoxide dismutase play key roles in removing reactive oxygen species (ROS) in many anaerobic microorganisms[9,10]
A previous study, using a proteomic approach to analyze changes in the cellular protein profiles of BBMN68 exposed to an inhibitory to sublethal concentration of oxygen (3%, v/v), revealed some key proteins involved in the response of BBMN68 to oxygen[16]
We used RNA-Seq transcriptome profiling to investigate the mechanism governing the response to oxygen in the potentially probiotic B. longum strain BBMN68
Summary
Enzymes such as NADH oxidase, NADH peroxidase, catalase and superoxide dismutase play key roles in removing ROS in many anaerobic microorganisms[9,10]. Bifidobacteria employ a particular set of proteins, mainly molecular chaperones and proteases, to protect the cells from damage caused by the accumulation of unfolded and/or misfolded proteins. These chaperones and proteases play key roles in several post-translational events to prevent protein denaturation, aggregation and misfolding caused by stresses, such as oxidative stress[19,20]. Next-generation RNA-sequencing (RNA-Seq) analysis and validation of physiological characteristics were employed to study the oxidative stress response and resistance mechanism in B. longum strain BBMN68
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