Relative rates and mechanisms of biodegradation of diester plasticizers mediated by Rhodococcus rhodochrous

Abstract

Di-ester plasticizers undergo slow degradation resulting in the release of recalcitrant, toxic metabolites in the environment. It is demonstrated here that the first and rate-limiting step in their co-metabolism by Rhodococcus rhodochrous is the hydrolysis of one ester bond. This mechanism is different than one proposed earlier for direct biodegradation of di-2-ethylhexyl phthalate. Also, using butyl butyrate as a reference compound to compare the relative rates of hydrolysis of different di-ester plasticizers, biodegradation rates were found to be strongly influenced by steric hindrances and solubility. Esterase activity associated with the hydrolysis of these bonds was located in the envelope of the bacterial cell. The esterase activity was not induced by specific substrates and was detected at all stages of growth. These considerations are important for the hydrolysis of recalcitrant plasticizers by a process of co-metabolism, which leads to a slow but steady overall rate of biodegradation. This suggests that as the growing reservoir of plasticizers in the environment slowly undergoes biotransformation, recalcitrant toxic metabolites will be continuously released.Les plastifiants diester subissent une dégradation lenteà la suite du rejet de métabolites toxiques récalcitrants dans l'environnement. Il aété démontré dans ces pages que la premièreétape, cinétiquement limitante, de leur cométabolisme par la bactérie Rhodococcus rhodochrous est l'hydrolyse d'une liaison ester. Ce mécanisme est différent de celui proposé précédemment concernant la biodégradation directe du phtalate d'éthyl-2-hexyle. Aussi, en employant le butyrate de butyle comme composé de référence afin de comparer les vitesses relatives de l'hydrolyse de différents plastifiants diester, on a observé que les vitesses de biodégradationétaient fortement influencées par les encombrements stériques et la solubilité. L'activité de l'estérase liéeà l'hydrolyse de ces liaisons se situait dans l'enveloppe de la cellule bactérienne. L'activité de l'estérase n'a pasété induite par des substrats particuliers et aété détectéeà toutes lesétapes de la croissance. Ces considérations sont importantes en vue de l'hydrolyse de plastifiants récalcitrants au moyen d'un procédé de cométabolisme, qui permet d'obtenir une vitesse de biodégradation lente, mais stable dans l'ensemble. Cette observation porteà croire que tant et aussi longtemps que le bassin croissant de plastifiants rejetés dans l'environnement sera soumisà une biotransformation lente, il y aura rejet perpétuel de métabolites toxiques récalcitrants.

Leaching of the plasticizer di(2-ethylhexyl)phthalate (DEHP) from plastic containers and the question of human exposure

“…Therefore, replacement compounds for DEHP must be well designed and thoroughly studied prior to widespread commercialization to avoid the types of problems observed with DEHP, such as its persistence in the environment and accumulation of toxic metabolites. DEHP has especially been shown to be rather resistant to biodegradation by microbes, likely due to the positioning of the two ester groups to one another, as well as the branching on the side chains (Erythropel et al 2013;Erythropel et al 2012;Gartshore et al 2003;Nalli et al 2002;Sauvageau et al 2009). Similarly, its most problematic metabolite MEHP is possibly even more recalcitrant than its parent compound (Amir et al 2005;Ejlertsson et al 1996;Erythropel et al 2012;Jonsson et al 2003).…”

“…2) is through de-esterification (i.e., hydrolysis of an ester bond) to its monoester (MEHP) followed by a second de-esterification step to its corresponding organic acid (phthalic acid). This is sometimes preceded by β-oxidation of the side chains or trans-esterification of the molecule, but these latter pathways result only in different lengths of the side chains (Liang et al 2008;Sauvageau et al 2009;Staples et al 1997). De-esterification is achieved by enzymatic degradation by esterases which are produced by many common microbes.…”

A Bibliometric Analysis of Research Trends in Biodegradation of Plastics

“…The top five authors are Cooper DG (n = 11, total citations = 315, h_index =8), Nicell JA (n = 9, total citations = 236, h_index = 7), Briassoulis D (n = 6, total citations = 510, h_index = 6), Degli-Innocenti, F (n = 5, total citations = 191, h_index = 5), and Tosin, M (n = 5, total citations = 189, h_index = 5)-Table 3. Most of the Cooper DG publications are focused on the application of microorganisms, such as Bacillus subtilis, Rhodococcus rhodochrous, Rhodotorula rubra, and aerobic mesophilic microorganisms, consisting of bacteria, fungi, and yeast, for the degradation of different plastic materials [31][32][33][34]. H_index is a true indicator of researchers' contribution and attainment but it is not suitable for assessing multidisciplinary fields [35,36].…”

Tuning the properties of polyhydroxybutyrate films using acetic acid via solvent casting

“…Thermal processing assisted by additives is the most cost effective and industrially relevant approach for large-scale production of PHB films. However, most of the additives that improve thermal processing can also reduce biodegradation rates, increase cost, generate toxic degradation products 17 18 or cause health hazards related to leaching of plasticizers 13 14 15 16 17 18 19 20 21 . Recent works are exploring eco-friendly plasticizers 22 23 , green polymer blend, composites 24 25 and additives 26 to overcome these drawbacks, but some of the issues with using additives still exists.…”