ABSTRACT
A recent paper published in Gut Microbes, namely “Prevention of enteric bacterial infections and modulation of gut microbiota with conjugated linoleic acids producing Lactobacillus in mice”, misdescribed the MCRA recombinant hydroxyl fatty acid-producing Lactobacillus casei as conjugated linoleic acid producer.
We recently read the paper entitled “Prevention of enteric bacterial infections and modulation of gut microbiota with conjugated linoleic acids producing Lactobacillus in mice,” by Peng et al. published in Gut Microbes with interest. We were very interested in the descriptions of some of the recombinant Lactobacillus casei strains in the manuscript and, in particular, those containing the mcra gene (myosin-cross-reactive protein, MCRA) which were described as those which produce conjugated linoleic acid (CLA), however, from previous lines of evidence these strains do not produce CLA but rather the hydroxyl fatty acid.
In the paper, Peng et al. characterized a genetic-modified L. casei strain and evaluated its health-associated benefits on the host in murine model. The research is valid and important for probiotic development. Unfortunately, the overexpressed gene, myosin cross-reactive antigen gene (mcra) from L. rhamnosus GG, was claimed as linoleate isomerase, which in our opinion is incorrect.
MCRA was originally predicted as a fatty acid isomerase in Streptococcus pyogenes,Citation1 however, researchers failed to confirm this activity enzymatically.Citation2 Then in 2010, it was identified as a fatty acid hydratase, which converted linoleic acid to 10-hydroxy-cis-12-octadecenoic acid (10-HOE), and 10,13-dihydroxyoctadecanoic acid (10,13-DiHOA).Citation3 Subsequently, a number of publications has confirmed the presence of MCRA in numerous bacteria (especially in lactic acid bacteria such as L. plantarum,Citation4–Citation7 L. acidophilus,Citation8,Citation9 L. rhamnosus,Citation8 Bifidobacterium breve,Citation10,Citation11 etc), and that it is an oleate hydratase or linoleate hydratase and not a linoleate isomerase.
Indeed, CLA production in Lactobacillus, at least in L. plantarum, is generally a multiple-step reaction with multiple intermediates, such as 10-HOE, 10-oxo-cis-12-octadecenoic, 10-oxo-trans-11-octadecenoic acid, and 10-hydroxy-trans-11-octadecenoic acid. The reactions are catalyzed by a three component enzyme complex, including MCRA, short-chain dehydrogenase/oxidoreductase (DH) and acetoacetatedecarboxylase (DC).Citation4,Citation5
The source of the L. rhamnosus mcra gene for these experiments in the paper was L. rhamnosus GG which itself is not a CLA producer.Citation12 As such it lacks the genetic determinants necessary for CLA production. Moreover, the L. rhamnosus mcra gene used in the paper has been previously identified as linoleate hydratase,Citation8 where detailed information was presented including the products formed from oleic acid and linoleic acid, respectively. In contrast, in the original paper published by the authors,Citation13 where the recombinant L. casei was originally constructed, neither CLA nor fatty acid products were presented. Therefore, description of MCRA as a “linoleate isomerase” is not appropriate in the two publications. Indeed, this expressing clone would more likely make 10-HOE rather than CLA. If, however, the recombinant strain does produce CLA, it would mean that the L. casei host strain would have to have DH and DC as well which could further metabolize the10-HOE generated by MCRA. I would suggest that the authors take these comments into consideration.
In defense of the work, we would like to emphasize that 10-HOE is a novel functional fatty acid and has some protective effects on the host.Citation14,Citation15 In this respect, the results presented are valid and meaningful for 10-HOE and its producer but not for CLA in our opinion based on the evidence presented above.
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References
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