Reviewer 1's Review

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The manuscript by Zhou et al. describes a screen to identify genes
required for expression of the Pseudomonas aeruignosa type III secretion system
(T3SS). The authors demonstrate the following; (i) transposon insertions in
spuE, spuH, and spuF result in a significant reduction in T3SS gene expression
(a previous study found that these gene products encode components of a
spermidine uptake transporter), (ii) spuE and spuE-H deletion mutants have the
same phenotype as the transposon insertion mutants, (iii) microarray analyses
demonstrate that disruption of the spermidine transporter specifically disrupts
T3SS gene expression without significantly effecting the expression of any other
genes, (iv) exogenous spermidine stimulates T3SS gene expression, (v)
disruption of the spermidine transporter reduces T3SS gene expression and
T3SS-dependent cytoxicity following co-culture with liver tissue, and (vi)
spermidine biosynthetic mutants have no affect on T3SS gene expression.
These experiments address an important issue, that being mechanisms that
control T3SS gene expression. This general topic has broad appeal for those
interested in gene regulation, pathogenesis, type III secretion, and pathogenesis.
In general the data largely support the arguments put forth. There are a few
instances in which the data may have been subject to over interpretation and
some of the experiment require additional controls.

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N.B. These are the general comments made by the reviewer when reviewing this paper in light of which the manuscript was revised. Specific points addressed during revision of the paper are not shown.