Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2011
Publication Date: 2/1/2012
Citation: Kruczek, C., Wachtel, M., Alabady, M., Payton, P.R., Colmer-Hamood, J., Hamood, A. 2012. Serum albumin alters the expression of Pseudomonas aeruginosa Iron Controlled Genes. Microbiology. 158:323-367. Interpretive Summary: Pseudomonas aeruginosa, which causes serious infections in immunocompromised patients, produces numerous virulence factors including exotoxin A and the siderophore pyoverdine. As production of these virulence factors is influenced by the host environment, we examined the effect serum has on global transcription within P. aeruginosa at different phases of growth. At early exponential phase, serum significantly enhanced expression of 154 genes, most repressed by iron and which carry binding sequences for the ferric uptake regulator Fur or the Fur-regulated sigma factor PvdS. Transcriptional fusion analyses confirmed serum enhances expression of toxA, pvdA, and their regulatory genes regA and pvdS, yet does not interfere with the repression of these genes by iron. The effect on regA expression does not occur through Fur but requires functional PvdS. While complement inactivation failed to eliminate this effect albumin absorption reduced the effect of serum on pvdS and regA expression. Albumin does not mediate this effect in its role as an iron-binding protein, since holotransferrin did not affect pvdA, pvdS, or regA expression. We propose serum albumin plays a critical role in P. aeruginosa virulence during early phases of infection by enhancing the expression iron16 controlled genes through a Fur-independent mechanism not related to albumin-associated iron.
Technical Abstract: The objectives of this study were to examine the effect serum on global transcription within P. aeruginosa at different phases of growth and the role of iron in this regulation. Results presented in this study suggest a novel mechanism through which serum regulates the expression of different P. aeruginosa genes. The essential feature of this mechanism is its occurrence at early stages of growth and under iron-limited conditions. As shown by the results of the microarray analysis and confirmed by the transcriptional and translational fusion analyses, most of the serum-regulated genes are involved in either iron acquisition iron transport or iron storage. However, regulation of these genes by serum is opposite to their regulation by iron. Several of these serum-regulated genes also contain a Fur box within their upstream regions. Many genes that do not contain the Fur box contain and IS box and are regulated by PvdS, which carries a Fur box. Dispite this, their regulation by serum does not appear to be directly related to either iron or Fur. The loss of functional Fur did not interfere with the regulation of PAO1 pvdS or regA by serum. Our results showed that the phenomenon did not occur in response to the depletion of the intracellular pool of iron. Similarly, serum did not interfere with the repression of these genes by exogenous iron. Additionally, serum did not interfere with the repression of these two genes by the potential exogenous iron-chelator, NE. Furthermore, the base medium that we utilized for different serum-related experiments was the iron-deficient TSB-DC. Therefore, it is unlikely that the observed serum-induced regulation of these genes is due to an iron-chelating activity witin the serum.