Abstract
Bacterial production of conjugated linoleic acid (CLA) has recently received great attention because of the potential health benefits of this fatty acid. Linoleic acid (LA) can be converted to CLA by several microorganisms, including bifidobacteria, possibly as a detoxification mechanism to avoid the growth inhibition effect of LA. In the present in vitro study, we investigated the gene expression landscape of the intestinal strain Bifidobacterium breve DSM 20213 when exposed to LA. Transcriptomic analysis using RNA-seq revealed that LA induced a multifactorial stress response in the test strain, including upregulation of genes involved in iron uptake and downregulation of genes involved in sugar and oligopeptide transport. We also observed reduced transcription of genes involved in membrane and pili biosynthesis. The upregulation of iron uptake was not related to any putative ability of LA to chelate Fe2+, but was somewhat linked to stress response. Furthermore, we demonstrated that LA increased reactive oxygen species (ROS) production in bacterial cells, activating an oxidative stress response. This response was proved by thioredoxin reductase transcription, and was primarily evident among bacteria cultured in the absence of cysteine. This is the first report of the potential mechanisms involved in bacterial LA transport and stress response in B. breve.
Highlights
The omega−6 fatty acid linoleic acid (LA) is a structural component of cell membranes, as well as a precursor of several types of eicosanoids that are involved in important physiological processes
We found that the relative intracellular MDA content significantly differed (p = 0.0117) between bacterial cells grown in MRS-cys-Linoleic acid (LA) (16.61 ± 4.03%) versus those grown in MRS-cys (5.88 ± 1.27%)
Bifidobacteria represent the dominant colonizers of the large intestine of infants during the first weeks of life [34], and play key roles in the human gut because of their glycan-degrading abilities [35] and their capacity to utilize human milk oligosaccharides (HMOs) [36,37]
Summary
The omega−6 fatty acid linoleic acid (LA) is a structural component of cell membranes, as well as a precursor of several types of eicosanoids that are involved in important physiological processes. Many CLA producers are lactic acid bacteria—in particular, various species of lactobacilli Within this group of bacteria, the putative linoleate isomerase is reportedly the key gene responsible for the bioconversion of LA into CLA [3], the mechanism remains unclear. O’Connell et al [7] used gas-liquid chromatography (GLC) to investigate the capacity of different bifidobacteria species to convert LA into CLA, and found that B. breve NCFB 2258 was the strain that best converted LA Both reports elucidated a strain-specific ability to convert LA into CLA. O’Connell et al [7] used an insertional mutation approach and found strong evidence that the mcrA gene was not involved in this process It is unclear why bacteria convert LA, but one of the best-supported hypotheses is that CLA production may be a detoxification mechanism adopted by the bacterial cells. We confirmed and verified our results using chemical and microbiological experiments
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