extraction and estimation of total siderophore, pyoverdine, and pyochelin from pseudomonas aeruginosa

Assessment of Siderophore Production from &lt;em&gt;Pseudomonas aeruginosa&lt;/em&gt; Isolates

Organisms require iron to perform various vital functions, such as electron transport and DNA replication1. Pseudomonas aeruginosa, a Gram-negative opportunistic pathogen, is known to possess a variety of virulence factors to establish infection in the host, among which one mechanism is siderophore formation2. During iron-depleting conditions, P. aeruginosa releases specialized molecules called siderophores, which quench iron from the surrounding environment. Siderophores chelate iron extracellularly, and the resulting ferric-siderophore complex is actively transported back to the cell3.
P. aeruginosa is known to produce two siderophores, pyoverdine and pyochelin. Pyoverdine is known to have a higher iron chelating affinity (1:1), whereas pyochelin is known to have a lesser iron chelating affinity (2:1)4. Pyochelin is also called a secondary siderophore because it has a lower iron chelating affinity5. The production and regulation of siderophores are actively controlled by Quorum Sensing (QS) systems in P. aeruginosa6.
Besides iron quenching, siderophores are also involved in regulating virulence factors and play an active role in biofilm formation7. Siderophores serve additional crucial roles, including involvement in cell signaling, defense against oxidative stress, and facilitation of interactions between microbial communities8. Siderophores are typically categorized based on the specific functional groups through which they chelate iron. The three primary bidentate ligands in this classification are catecholate, hydroxamate, and &#945;-hydroxycarboxylate3. Pyoverdines are hallmarks of fluorescent Pseudomonas species such as P. aeruginosa and P. fluorescens5. They consist of a mixed green fluorescent chromophore coupled to an oligopeptide containing 6-12 amino acids. Several non-ribosomal peptide synthetases (NRPs) are involved in their synthesis9. Four genes involved in pyoverdine production and regulation are pvdL, pvdI, pvdJ, and pvdD10. Pyoverdine is also responsible for infection and virulence in mammals11. P. aeruginosa is noted to produce pyochelin in moderate iron-limiting conditions, while pyoverdine is produced during severe iron-limiting environments12. Two operons involved in pyochelin production are pchDCBA and pchEFGHI13. It is noted that in the presence of pyocyanin, pyochelin (catecholate) induces oxidative damage and inflammation and generates hydroxyl radicals, which are harmful to host tissues11.
The Chrome Azurol Sulfonate (CAS) assay is widely adopted due to its comprehensiveness, high sensitivity, and greater convenience compared to microbiological assays, which, although sensitive, can be overly specific14. The CAS assay can be conducted on agar surfaces or in a solution. It relies on the color change that occurs when the ferric ion transitions from its intense blue complex to orange. The CAS colorimetric assay quantifies the depletion of iron from a Fe-CAS-surfactant ternary complex. This particular complex, consisting of metal, organic dye, and surfactant, has a blue color and exhibits an absorption peak at 630 nm.
This report presents a method for the qualitative detection of siderophore production, where one can detect the production of siderophores on an agar plate. A method for the quantitative estimation of total siderophore production in a microtiter plate and the detection and quantitative analysis of two siderophores, pyoverdine and pyochelin, from P. aeruginosa, is also provided.

Author Spotlight: Quantifying Siderophores and Pyochelin for Infection Control 

Qualitative and Quantitative Analysis of Siderophore Production from Pseudomonas aeruginosa

Siderophores form complexes with iron and transport it into the cell during iron-limiting conditions. Siderophores are potent virulence factors which help in establishing severe infection in the host, and are known to play a role in regulating quorum sensing in Pseudomonas aeruginosa. Our research aims to quantitatively estimate siderophore production in Pseudomonas.Siderophores are extracellular molecules, so total siderophores, along with pyoverdine and pyochelin are quantified using cell-free supernatant. As pyochelin is not detected in small volume, extraction is performed from a large volume of cell-free supernatant. Recently, LCMS and biosensors have been developed for quantification of pyochelin.LCMS is a costly setup for small laboratories, whereas biosensors are capable of quantification of pyochelin only. This simple and illustrated protocol uses minimum laboratory reagents and instrumentation, and allows siderophore's estimation from cell-free supernatant using less time.

Watch this Scientific Journal Video about Extraction and Estimation of Total Siderophore, Pyoverdine, and Pyochelin from Pseudomonas aeruginosa at JoVE.com

Extraction and Estimation of Total Siderophore, Pyoverdine, and Pyochelin from Pseudomonas aeruginosa  

Extraction and Estimation of Total Siderophore, Pyoverdine, and Pyochelin from Pseudomonas aeruginosa

extraction-estimation-total-siderophore-pyoverdine-pyochelin-from

Research

JoVE Journal

Biology

605 Views.  The Maharaja Sayajirao University of Baroda. Extraction and Estimation of Total Siderophore, Pyoverdine, and Pyochelin from Pseudomonas aeruginosa

Video: Extraction and Estimation of Total Siderophore, Pyoverdine, and Pyochelin from Pseudomonas aeruginosa  

Pseudomonas aeruginosa (P. aeruginosa) is known for its production of a diverse range of virulence factors to establish infections in the host. One such mechanism is the scavenging of iron through siderophore production. P. aeruginosa produces two different siderophores: pyochelin, which has lower iron-chelating affinity, and pyoverdine, which has higher iron-chelating affinity. This report demonstrates that pyoverdine can be directly quantified from bacterial supernatants, while pyochelin needs to be extracted from supernatants before quantification.
The primary method for qualitatively analyzing siderophore production is the Chrome Azurol Sulfonate (CAS) agar plate assay. In this assay, the release of CAS dye from the Fe3+-Dye complex leads to a color change from blue to orange, indicating siderophore production. For the quantification of total siderophores, bacterial supernatants were mixed in equal proportions with CAS dye in a microtiter plate, followed by spectrophotometric analysis at 630 nm. Pyoverdine was directly quantified from the bacterial supernatant by mixing it in equal proportions with 50 mM Tris-HCl, followed by spectrophotometric analysis. A peak at 380 nm confirmed the presence of pyoverdine. As for Pyochelin, direct quantification from the bacterial supernatant was not possible, so it had to be extracted first. Subsequent spectrophotometric analysis revealed the presence of pyochelin, with a peak at 313 nm.

This protocol provides both qualitative and quantitative analyses of total siderophores, pyoverdine, and pyochelin from Pseudomonas aeruginosa.

Pseudomonas aeruginosa (P. aeruginosa) is known for its production of a diverse range of virulence factors to establish infections in the host. One such ...