Cyanate Assimilation by the Alkaliphilic Cyanide-Degrading Bacterium Pseudomonas pseudoalcaligenes CECT5344: Mutational Analysis of the cyn Gene Cluster.

Lara Paloma Sáez,Conrado Moreno-Vivián,María Dolores Roldán,Purificación Cabello,María Isabel Ibáñez,Víctor Manuel Luque-Almagro

doi:10.3390/ijms20123008

Lara Paloma Sáez, Conrado Moreno-Vivián + Show 4 more

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https://doi.org/10.3390/ijms20123008

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Abstract

The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 can grow with cyanate, cyanide, or cyanide-containing industrial residues as the sole nitrogen source, but the assimilation of cyanide and cyanate takes place through independent pathways. Therefore, cyanide degradation involves a chemical reaction between cyanide and oxaloacetate to form a nitrile that is hydrolyzed to ammonium by the nitrilase NitC, whereas cyanate assimilation requires a cyanase that catalyzes cyanate decomposition to ammonium and carbon dioxide. The P. pseudoalcaligenes CECT5344 cynFABDS gene cluster codes for the putative transcriptional regulator CynF, the ABC-type cyanate transporter CynABD, and the cyanase CynS. In this study, transcriptional analysis revealed that the structural cynABDS genes constitute a single transcriptional unit, which was induced by cyanate and repressed by ammonium. Mutational characterization of the cyn genes indicated that CynF was essential for cynABDS gene expression and that nitrate/nitrite transporters may be involved in cyanate uptake, in addition to the CynABD transport system. Biodegradation of hazardous jewelry wastewater containing high amounts of cyanide and metals was achieved in a batch reactor operating at an alkaline pH after chemical treatment with hydrogen peroxide to oxidize cyanide to cyanate.

Highlights

Cyanide is a toxic chemical that inhibits different metalloproteins by its binding to the metal cofactors
The alkaliphilic cyanide-degrading bacterium P. pseudoalcaligenes CECT5344 harbors a cyn gene cluster (Figure 1A) that includes the cynF gene encoding a putative transcriptional regulator of the Fis family and the structural cynABDS genes, which are transcribed in the opposite direction to cynF and code for the periplasmic component, the inner membrane subunit and the cytosolic ATPase protein of a putative ABC-type cyanate transporter, and the enzyme cyanase, respectively [43]
Considering that P. pseudoalcaligenes CECT5344 possesses the cyn genes required for cyanate assimilation, the cioAB genes involved in cyanide tolerance, and the nitC1 gene cluster needed for the assimilation of cyanide and nitriles, this strain is a good candidate to be used in the detoxification of industrial wastewaters containing both cyanide and cyanate as co-contaminants

Summary

Introduction

Cyanide is a toxic chemical that inhibits different metalloproteins by its binding to the metal cofactors. The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 grows with free cyanide or metal–cyanide complexes as the sole nitrogen source under alkaline conditions (pH 9.5–10), avoiding cyanide volatilization [7,9,10]. In this bacterium, the cyanide degradation pathway requires a malate:quinone oxidoreductase that converts malate into oxaloacetate, which reacts chemically with cyanide, forming a cyanohydrin (hydroxynitrile) that is further hydrolyzed by the nitrilase NitC encoded by the nit1C gene cluster, generating ammonium [11,12]

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