Photoheterotrophic Metabolism of Acrylamide by a Newly Isolated Strain of Rhodopseudomonas palustris

Abstract

Acrylamide, a neurotoxin and suspected carcinogen, is produced by industrial processes and during the heating of foods. In this study, the microbial diversity of acrylamide metabolism has been expanded through the isolation and characterization of a new strain of Rhodopseudomonas palustris capable of growth with acrylamide under photoheterotrophic conditions. The newly isolated strain grew rapidly with acrylamide under photoheterotrophic conditions (doubling time of 10 to 12 h) but poorly under anaerobic dark or aerobic conditions. Acrylamide was rapidly deamidated to acrylate by strain Ac1, and the subsequent degradation of acrylate was the rate-limiting reaction in cell growth. Acrylamide metabolism by succinate-grown cultures occurred only after a lag period, and the induction of acrylamide-degrading activity was prevented by the presence of protein or RNA synthesis inhibitors. 13 Acrylamide is a toxic three-carbon compound containing an amide group and an ␣,␤-unsaturated olefin bond. It exerts its toxic effects by forming adducts to nucleophilic moieties such as sulfhydryl groups on proteins (4). Acrylamide is potent neurotoxin (30) and suspected to be a carcinogen (21, 27). Although acrylamide is not typically found in nature, it is widely used in industrial processes as a polymerizing agent, hardener, and as a flocculent in water treatment. Accordingly, acrylamide released from industrial processes has resulted in the contamination of both soils and aquatic environments (6). Recently, it was discovered that acrylamide is formed in starchy foods after being cooked at the high temperatures required for frying and baking (26,27). These foods, which have undetectable levels before cooking, have acrylamide levels as high as 2.3 mg/kg after cooking (25). The formation of acrylamide is believed to be a product of the reaction between asparagine and glucose during the cooking process (14, 24).In spite of acrylamide's toxicity in the monomer form, some microorganisms are able to utilize acrylamide as their sole carbon source for growth (16,17,22,32,33). All studies conducted to date show that there is an initial deamidation step that converts acrylamide to acrylic acid (acrylate) (15,17,22,33). The subsequent fate of acrylate has not been well defined for acrylamideutilizing bacteria but probably involves pathways and enzymes that have been characterized to various degrees for other bacteria capable of acrylate catabolism. In aerobic acrylate-utilizing bacteria, acrylate metabolism has been shown to proceed via hydroxylation to ␤-hydroxypropionate, which is further oxidized to CO 2 (1, 2). Highlighting a different fate for acrylate under anaerobic conditions, Clostridium propionicum is capable of fermenting acrylate to acetate and propionate (10). Acrylate has also been shown to serve as a terminal electron acceptor for Desulfovibrio acrylicus, producing propionate which is not further metabolized as a growth substrate (31). Cell extracts of C. propionicum have been shown to dehydrate (R)-lactate to acrylate (20)...

Transfer and degradation of polyacrylamide-based flocculants in hydrosystems: a review

“…For AMD degrading-bacteria, AA is probably reduced to generate energy for bacterial growth but the catabolic pathway is not clear. Wampler and Ensign (2005) suggested that AA is degraded to β-hydropropionate via hydroxylation reaction, then oxidized to CO 2 or reduced to propionic acid. Recently, Charoenpanich and Tani (2014) have studied the response of an acrylamidedegrader Enterococcus aerogenes to AMD using proteome analysis.…”

Evaluation of acrylamide-removing properties of two Lactobacillus strains under simulated gastrointestinal conditions using a dynamic system

“…In this last respect, bacteria capable of utilizing acrylamide in vitro as the sole carbon and nitrogen source have been isolated (Wampler and Ensign, 2005). Furthermore, recent studies have shown that some lactic acid bacteria such as Lactobacillus reuteri NRRL 14171 and Lactobacillus casei Shirota, possess the capability to remove acrylamide in aqueous solution by physically binding of the toxin to the bacterial cell wall (Serrano-Niño et al, 2015;.…”

Removal of Acrylamide by Microorganisms

“…Since 1982, microbial degradation of acrylamide has been explored extensively with a diversity of isolates (Table 1), mainly Bacillus, Pseudomonas and Rhodococcus [3,[46][47][48][49][50][51][52][53][54][55]. Further, numerous other microorganisms including the representatives of Arthrobacter, Xanthomonas, Rhodopseudomonas, Rastonia, Geobacillus, and a newly family of Enterobacteriaceae [49,[56][57][58][59][60][61][62]. Aspergillus oryzae, a filamentous fungal has also been documented as an acrylamide degrader [63].…”

“…Recently a new strain of Rhodopseudomonas palustris was found capable of using acrylamide under photoheterotrophic conditions but grew poorly under anaerobic dark or aerobic conditions. A study of acrylamide metabolism by nuclear magnetic resonance showed the rapid deamidation of acrylamide to acrylate and further to propionate [57]. More recently, the denitrifying bacterium, Ralstonia eutropha TDM-3 isolated from the wastewater treatment system associated with the manufacture of polyacrylonitrile fiber consumed acrylamide to concentration of 1446 mg/l, above which it was toxic [58].…”