Exploring anaerobic environments for cyanide and cyano-derivatives microbial degradation

Abstract

Cyanide is one of the most toxic chemicals for living organisms described so far. Its toxicity is mainly based on the high affinity that cyanide presents toward metals, provoking inhibition of essential metalloenzymes. Cyanide and its cyano-derivatives are produced in a large scale by many industrial activities related to recovering of precious metals in mining and jewelry, coke production, steel hardening, synthesis of organic chemicals, and food processing industries. As consequence, cyanide-containing wastes are accumulated in the environment becoming a risk to human health and ecosystems. Cyanide and related compounds, like nitriles and thiocyanate, are degraded aerobically by numerous bacteria, and therefore, biodegradation has been offered as a clean and cheap strategy to deal with these industrial wastes. Anaerobic biological treatments are often preferred options for wastewater biodegradation. However, at present very little is known about anaerobic degradation of these hazardous compounds. This review is focused on microbial degradation of cyanide and related compounds under anaerobiosis, exploring their potential application in bioremediation of industrial cyanide-containing wastes.

Role of the Dihydrodipicolinate Synthase DapA1 on Iron Homeostasis During Cyanide Assimilation by the Alkaliphilic Bacterium Pseudomonas pseudoalcaligenes CECT5344

“…Chemical treatments to remove cyanide from industrial wastewaters are very expensive and generate products that are also toxic. Therefore, biological treatments to remove cyanide from cyanide-containing wastewaters have been applied successfully (Dubey and Holmes, 1995;Dash et al, 2009;Cabello et al, 2018;Luque-Almagro et al, 2018). Considering that cyanide inhibits aerobic respiration, microorganisms that grow with cyanide contain a cytochrome bd-type cyanide-insensitive alternative oxidase (Jünemann, 1997).…”

“…These "cyanotrophic" microorganisms also require a cyanide degradation route. In this sense, several pathways for cyanide degradation that include hydrolytic, oxidative or substitution/addition reactions have been described (Cabello et al, 2018;Luque-Almagro et al, 2018). However, most of these degradative pathways operate at neutral pH, while an alkaline pH is required to avoid the volatilization of cyanhydric acid.…”

Putative small RNAs controlling detoxification of industrial cyanide-containing wastewaters by Pseudomonas pseudoalcaligenes CECT5344

“…Cyanide is a natural compound that is produced by living organism with offensives or defensive purposes. Cyanogenic organisms that are capable to produce cyanide include bacteria, algae, fungi and plants [1,2]. Numerous genera of cyanogenic bacteria have been described like Chromobacterium , Burkholderia and Pseudomonas , and several of their genomes have been sequenced recently [3,4,5].…”

“…In this sense, cyanogenic bacteria constitute a source of cyanide for metal bioleaching, forming soluble metal–cyanide complexes from solid materials [6,7,8]. By contrast, only a few genera of bacteria have been described to metabolize cyanide through different oxidative, reductive, hydrolytic or substitution/transfer pathways [2,9,10,11,12], and/or organic nitriles, which are assimilated by nitrilases or nitrile hydratases [2,13]. Most cyanide-degrading microorganisms grow best around neutral pH, which could be an inconvenience to assimilate cyanide because at neutral pH cyanide evaporates as cyanhydric acid (pKa 9.3).…”

Interplay of nucleophilic catalysis with proton transfer in the nitrile reductase QueF from Escherichia coli

“…Enzymatic transformations of the nitrile group are important biologically, for example, in secondary and xenobiotic metabolisms of plants and microorganisms. [1][2][3] They also have significant applications in synthetic chemistry wherein nitriles often represent important intermediates. 4,5 The nitrile group is converted by hydrolytic enzymes to an amide or to a carboxylic acid [6][7][8][9] and by reductive enzymes to an amine.…”