Cyanide degradation by Pseudomonas pseudoalcaligenes CECT5344 involves a malate : quinone oxidoreductase and an associated cyanide-insensitive electron transfer chain

Abstract

The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 is able to grow with cyanide as the sole nitrogen source. Membrane fractions from cells grown under cyanotrophic conditions catalysed the production of oxaloacetate from L-malate. Several enzymic activities of the tricarboxylic acid and glyoxylate cycles in association with the cyanide-insensitive respiratory pathway seem to be responsible for the oxaloacetate formation in vivo. Thus, in cyanide-grown cells, citrate synthase and isocitrate lyase activities were significantly higher than those observed with other nitrogen sources. Malate dehydrogenase activity was undetectable, but a malate : quinone oxidoreductase activity coupled to the cyanide-insensitive alternative oxidase was found in membrane fractions from cyanide-grown cells. Therefore, oxaloacetate production was linked to the cyanide-insensitive respiration in P. pseudoalcaligenes CECT5344. Cyanide and oxaloacetate reacted chemically inside the cells to produce a cyanohydrin (2-hydroxynitrile), which was further converted to ammonium. In addition to cyanide, strain CECT5344 was able to grow with several cyano derivatives, such as 2-and 3-hydroxynitriles. The specific system required for uptake and metabolization of cyanohydrins was induced by cyanide and by 2-hydroxynitriles, such as the cyanohydrins of oxaloacetate and 2-oxoglutarate.

A Cyanide-Induced 3-Cyanoalanine Nitrilase in the Cyanide-Assimilating Bacterium Pseudomonas pseudoalcaligenes Strain CECT 5344

“…13 also assimilates 3-cyanoalanine, and this compound is the inducer of the nitrilase activity (47). In contrast, it has been reported that in Pseudomonas pseudoalcaligenes CECT 5344 3-cyanoalanine does not induce the cyanide assimilation pathway (40), and here we demonstrate that the inducer of the nit4 gene is clearly cyanide (Fig. 1B and 6A) and that 3-cyanoalanine is much more efficiently assimilated in the presence of cyanide (Fig.…”

“…A putative nitrilase gene homologous to the gene encoding the 3-cyanoalanine nitrilase described in plants (nit4) was detected among the four putative nitrilase genes in the genome of P. pseudoalcaligenes CECT 5344 (38). Moreover, P. pseudoalcaligenes CECT 5344 has been reported to be able to assimilate 3-cyanoalanine (40). Since there are not published antecedents concerning either the assimilation pathway of 3-cyanoalanine in this strain or its role in cyanide assimilation, the presence of a putative 3-cyanoalanine nitrilase activity was studied.…”

“…In Pseudomonas pseudoalcaligenes CECT 5344, it was described that 2-oxoacids chemically react with free-cyanide-producing 2-hydroxynitriles, which can be theoretically converted into ammonium by either a nitrilase or a nitrile hydratase-amidase system (40). Nevertheless, the precise pathway for cyanide assimilation is unknown.…”

“…Targeted disruption of nit4 gene in P. pseudoalcaligenes CECT 5344. As stated before, the strain CECT 5344 was described to be able to use 3-cyanoalanine as the sole nitrogen source (40). Then, in order to check the putative role of Nit4 in the assimilation of cyanide and this nitrile, the phenotype of a mutant in the corresponding gene was studied.…”

Biodesulphurization of thiophene as a sulphur model compound in crude oils by Pseudomonas aeruginosa supported on polyethylene

“…However, few studies have evaluated the influence of inorganic supports on the BDS activity and using polymers as the support for bacterial strain for BDS never have been observed [32,33]. Pseudomonas species are able to grow with cyanide as the sole nitrogen source and several enzyme activities of these bacterial strains were significantly higher than those observed with other nitrogen sources [34]. Also the bacterial cells exhibited a greater extent and rate of biodegradation in the presence of ferricyanide as the terminal electron acceptor compared to the individual cells [35].The purpose of this study is to investigate biodesulphurization ability of P. aeruginosa supported on polyethylene in the presence of potassium hexacyanoferrate(III) in thiophene biodegradation as an aromatic sulphur model compound of crude oil.…”