Reader Comments

Post a new comment on this article

Referee Comments: Referee 2

Posted by PLOS_ONE_Group on 27 May 2008 at 08:57 GMT

Referee 2's review:

N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication, the manuscript has been revised in light of these comments and to address other editorial requirements.

Summary: This paper uses in vitro studies to describe the roles of 3 proteins in Fe uptake in M. tuberculosis, with some parallel genetic studies carried out with gene homologs in M. smegmatis. It appears technically sound and it contributes new and useful information. Hence it is appropriate for publication.


Probably the greatest weakness of the paper is its failure to adequately address J. Bact. 2006, 188, 424-430 by Rodriguez and Smith (reference 11). That paper identified Rv1348 and Rv1349 as components of an ABC transporter (i.e., carboxymycobactin importer), and suggested that they formed a heterodimer. This putative transporter was in turn compared to YbtP and YbtQ from Yersinia pestis (Mol. Microbiol. 1999, 32, 289-299). Because the authors appear to contradict the published account of Rodriguez and Smith, it is critical that they summarize the principal results from this paper and give more detailed commentary on how their own data add to the emerging model.

The constants measured for binding of ferrated/deferrated siderophores to the two siderophore bidning proteins are fairly similar. It may be an overstatement to say that Rv1348 has true specificity for ferrated siderophores, and Rv2895c for deferrated siderophores.

Also, I may have missed the appropriate data in the paper, but were the following controls done? If so, perhaps a word or two about the results would be helpful, as I missed them:

(1) pull-down assays for Rv1349/rRv2895c in the absence of siderophore, and in the presence of deferrated siderophore

(2) liposome reconstitution experiments with only rRv1349 and only rRv2895c, in addition to the rRv1349-rRv2895c combination

Finally, the authors analyzed the interior of their liposomes for carboxymycobactin content via the fluorescence emission of the lysed pellet fraction. Similar transport assays are often done by monitoring the flux of radioactive Fe. Can the authors comment on the error analysis involved in their procedure? Were control experiments done? For example, how much apparent uptake/efflux occurs in the absence of one or more of the proteins? Will other molecules, e.g., fluorescent non-siderophores, be transported? Is mycobactin transported? These data are so critical to the main findings of the paper, so fleshing out of details and addition of controls to this section would be most useful.

Who would find this paper of interest? And why?

Scientists working with TB and other Mycobacteria would find this paper of interest as it describes components of the Fe uptake apparatus of these organisms. Fe is an essential bionutrient and therefore a key element for biocontrol. Scientists interested in microbial metal trafficking would likewise find it of interest, as Mycobacteria have their own, sometimes unusual.