On 2017 Dec 04, Anthony Michael commented:

This paper tackles an interesting problem: whether Salmonella needs to be able to N-acetylate the polyamines spermidine or spermine for successful intracellular replication in human cells. Acetylation of endogenous spermidine in Salmonella might be required to prevent excess/ deleterious accumulation of spermidine. Acetylation by Salmonella of host-derived spermine might detoxify a potentially physiologically disruptive metabolite.

  Until this paper, the tetraamine spermine has never been reproducibly detected in Enterobacteria, however, the authors find that spermine is present in Salmonella at 8.0 mM and is 40 times more abundant than spermidine in Salmonella cells. Such a high molar ratio of spermine to spermidine has never been found in any organism, not even in seminal fluid, where spermine phosphate is sufficiently concentrated to result in some crystallization. This is an extraordinary discovery if reproducible, although it is more likely that some technical problem lies at the heart of this unique finding.

   It should be noted that the authors grew the Salmonella in LB medium, a rich, putrescine- and spermidine-containing medium. To determine the native polyamines of a given bacterial species, it is necessary to grow the bacterium in polyamine-free, chemically-defined medium because most bacteria can take up polyamines from the environment. There is barely detectable spermine in LB medium, and so the presence of spermine at 8 mM is all the more remarkable (this is likely a higher concentration of spermine than found in the human host cells, which have a dedicated spermine synthase not found in Salmonella). I suggest the authors use LC-MS to detect the mass of tetrabenzoylated spermine in their benzoylated extracts of Salmonella. Finally, the authors have not demonstrated that the spermidine N-acetyltransferase (speG) gene deletion results in any change in N-acetylspermidine levels. As the Salmonella speG protein has not been previously biochemically characterized, it would be prudent to seek orthogonal proof that the changes ascribed to the speG gene deletion are due to its enzymatic activity as a spermidine N-acetyltransferase. If spermine is reproducibly found to be present in Salmonella at 8.0 mM, I am more than happy to admit that everything that I know is wrong.

On 2017 Dec 04, Anthony Michael commented:

This paper tackles an interesting problem: whether Salmonella needs to be able to N-acetylate the polyamines spermidine or spermine for successful intracellular replication in human cells. Acetylation of endogenous spermidine in Salmonella might be required to prevent excess/ deleterious accumulation of spermidine. Acetylation by Salmonella of host-derived spermine might detoxify a potentially physiologically disruptive metabolite.

  Until this paper, the tetraamine spermine has never been reproducibly detected in Enterobacteria, however, the authors find that spermine is present in Salmonella at 8.0 mM and is 40 times more abundant than spermidine in Salmonella cells. Such a high molar ratio of spermine to spermidine has never been found in any organism, not even in seminal fluid, where spermine phosphate is sufficiently concentrated to result in some crystallization. This is an extraordinary discovery if reproducible, although it is more likely that some technical problem lies at the heart of this unique finding.

   It should be noted that the authors grew the Salmonella in LB medium, a rich, putrescine- and spermidine-containing medium. To determine the native polyamines of a given bacterial species, it is necessary to grow the bacterium in polyamine-free, chemically-defined medium because most bacteria can take up polyamines from the environment. There is barely detectable spermine in LB medium, and so the presence of spermine at 8 mM is all the more remarkable (this is likely a higher concentration of spermine than found in the human host cells, which have a dedicated spermine synthase not found in Salmonella). I suggest the authors use LC-MS to detect the mass of tetrabenzoylated spermine in their benzoylated extracts of Salmonella. Finally, the authors have not demonstrated that the spermidine N-acetyltransferase (speG) gene deletion results in any change in N-acetylspermidine levels. As the Salmonella speG protein has not been previously biochemically characterized, it would be prudent to seek orthogonal proof that the changes ascribed to the speG gene deletion are due to its enzymatic activity as a spermidine N-acetyltransferase. If spermine is reproducibly found to be present in Salmonella at 8.0 mM, I am more than happy to admit that everything that I know is wrong.