Endogenous phenazine-1-carboxamide encoding gene PhzH regulated the extracellular electron transfer in biocorrosion of stainless steel by marine Pseudomonas aeruginosa

Abstract

Extracellular electron transfer (EET) is believed to be a bottleneck in microbiologically influenced corrosion (MIC), also known as biocorrosion, by electro-active microbes. However, there is a lack of any direct evidence at the genetic level to confirm this so far in the literature. In this work, water-soluble electron transfer mediator molecule phenazine‑1‑carboxamide (PCN) produced by Pseudomonas aeruginosa was found to mediate the EET between P. aeruginosa and 2205 DSS (duplex stainless steel), thus regulating the corrosion rate. The phzH gene in P. aeruginosa encodes the enzyme which converts PCA (phenazine‑1‑carboxamide) to PCN. A P. aeruginosa mutant strain with phzH knockout (ΔphzH strain) and a strain with phzH restored (phzH-complemented mutant, phzH-comp.) were genetically engineered to confirm that phzH regulates EET-MIC of 2205 DSS by P. aeruginosa. Various electrochemical corrosion data in this work demonstrated that the corrosion rate decreased considerably after knocking out phzH and it largely recovered after phzH was restored. For the first time, it was demonstrated that a gene responsible for the production of an electron transfer mediator in P. aeruginosa regulated MIC, thus confirming at the genetic level that EET is a bottleneck in the MIC by P. aeruginosa.