Characterization of Klebsiella sp. strain S1: a bacterial producer of secoisolariciresinol through biotransformation.

Secoisolariciresinol (SECO) is a lignan of potential therapeutic value for diseases such as cancer, but its use has been limited by the lack of ideal production methods, even though its precursors are abundant in plants, such as flaxseeds. Here, we report the characterization of a bacterial strain, S1, isolated from the human intestinal flora, which could produce secoisolariciresinol by biotransformation of precursors in defatted flaxseeds. This bacterium was a Gram-negative and facultatively anaerobic straight rod without capsules. Biochemical assays showed that it was negative for production of oxidase, lysine decarboxylase, ornithine decarboxylase, arginine dihydrolase, and β-glucolase. The G + C content of genomic DNA was 57.37 mol%. Phylogenetic analysis by 16S rRNA and rpoB gene sequences demonstrated S1's close relatedness to Klebsiella. No homologues were found for wzb or wzc (capsular genes), which may explain why Klebsiella sp. strain S1 does not have the capsule and was isolated from a healthy human individual. Based on the percentages of homologous genes with identical nucleotide sequences between the bacteria in comparison, we found that clear-cut genetic boundaries had been formed between S1 and any other Klebsiella strains compared, dividing them into distinct phylogenetic lineages. This work demonstrates that the intestinal Klebsiella, well known as important opportunistic pathogens prevalent in potentially fatal nosocomial infections, may contain lineages that are particularly beneficial to the human health.