The Discovery and Biological Mechanisms of a Widespread Phenazine's Oxidation

Abstract

During the 2017 Microbial Diversity course at the Marine Biological Laboratory in Woods Hole, MA, Scott Saunders and Yinon Bar-On started enrichment cultures in hopes of discovering biological oxidation of phenazine-1-carboxylic acid (PCA). I took these enrichment cultures and described their PCA oxidation activity. From one of the mixed cultures, I isolated a bacterial strain that recapitulated the behavior of the enrichment. I identified it as a strain of Citrobacter portucalensis via a whole-genome analysis and called the strain "MBL" in reference to the Marine Biological Laboratory. Using a combination of analytical chemistry, quantitative fluorescence measurements, and genetic engineering, I showed that C. portucalensisMBL couples PCA oxidation to each mode of anaerobic respiration it employs with nitrate, fumarate, dimethyl sulfoxide (DMSO), and trimethylamine-N-oxide (TMAO) as terminal electron acceptors(TEAs). I further found that most of the PCA oxidation activity depends on electron flux through the quinone/quinol pool but can be driven by certain terminal reductase complexes when no quinones are available, particularly in the case of nitrate reductases. Every bacterial strain I tested catalyzed PCA oxidation when provided the appropriate TEA. My described mechanism for bacterial PCA oxidation is generalizable and implies that this previously undocumented phenomenon should occur wherever PCA is produced in rhizosphere environments.