Hydrolysis of 4-Hydroxybenzoic Acid Esters (Parabens) and Their Aerobic Transformation into Phenol by the Resistant Enterobacter cloacae Strain EM

Abstract

Enterobacter cloacae strain EM was isolated from a commercial dietary mineral supplement stabilized by a mixture of methylparaben and propylparaben. It harbored a high-molecular-weight plasmid and was resistant to high concentrations of parabens. Strain EM was able to grow in liquid media containing similar amounts of parabens as found in the mineral supplement (1,700 and 180 mg of methyl and propylparaben, respectively, per liter or 11.2 and 1.0 mM) and in very high concentrations of methylparaben (3,000 mg liter ؊1 , or 19.7 mM). This strain was able to hydrolyze approximately 500 mg of methyl-, ethyl-, or propylparaben liter ؊1 (3 mM) in less than 2 h in liquid culture, and the supernatant of a sonicated culture, after a 30-fold dilution, was able to hydrolyze 1,000 mg of methylparaben liter ؊1 (6.6 mM) in 15 min. The first step of paraben degradation was the hydrolysis of the ester bond to produce 4-hydroxybenzoic acid, followed by a decarboxylation step to produce phenol under aerobic conditions. The transformation of 4-hydroxybenzoic acid into phenol was stoichiometric. The conversion of approximately 500 mg of parabens liter ؊1 (3 mM) to phenol in liquid culture was completed within 5 h without significant hindrance to the growth of strain EM, while higher concentrations of parabens partially inhibited its growth.

Occurrence, fate and risk assessment of parabens and their chlorinated derivatives in an advanced wastewater treatment plant

“…Previous study has shown PHBA was refractory to anaerobic biological treatment [39], leading to little change of PHBA in anaerobic tank and anoxic tank. Additionally, it is reported that the first step of parabens degradation was the hydrolysis of the ester bond to produce PHBA under aerobic condition [40]. Therefore, this result suggests that some PHBA, the main microbial degradation metabolite of parabens, was formed by degradation of parabens during the activated sludge treatment, which resulted in the increase of PHBA levels in oxic tank and secondary clarifier.…”

Phytochemical Composition of <i>Tridax procumbens</i> Linn Leaves: Potential as a Functional Food

“…Caffeic acid has anti-diabetic [50], antioxidant [62], anti-inflammatory and photo-protective [63] activities. 4-Hydroxybenzoic acid esters (also called parabens), are widely used as antimicrobial agents in a large variety of food, pharmaceutical, and cosmetic products due to their excellent antimicrobial activities, low toxicity and stability over a wide pH range [64]. 4-Hydroxybenzoic acid has antifungal, anti-mutagenic, anti-sickling, estrogenic and antimicrobial [62] activities.…”

prbA , a Gene Coding for an Esterase Hydrolyzing Parabens in Enterobacter cloacae and Enterobacter gergoviae Strains

“…At the beginning and end of the 2-h incubation, aliquots were removed and heated immediately to 80°C for 10 min in order to prevent further enzymatic degradation of the parabens. The amount of parabens remaining in the samples and the appearance of p-hydroxybenzoic acid was then analyzed by high-performance liquid chromatography as previously described (26). The presence of homologues of prbA in selected strains was determined by touchdown PCR with the primers and conditions specified above.…”

“…The amplified gene was ligated into the pGEM-T Easy vector and transformed into competent E. coli DH5␣ cells. The hydrolysis of 600 mg of methyl paraben liter Ϫ1 (4.0 mM) in TSB growth medium was monitored at 37°C as previously described (26).…”

“…Recently, we described the Enterobacter cloacae strain EM, which was isolated from a contaminated batch of a commercial mineral supplement normally well stabilized with a mixture of 1,700 mg of methyl paraben liter Ϫ1 (11.2 mM) and 180 mg of propyl paraben liter Ϫ1 (1.0 mM). This strain demonstrated a very high resistance to the parabens attributed to the action of an esterase (26). Here, we report the cloning and sequencing of the gene named prbA coding for this esterase, which is responsible for the hydrolysis of the parabens, and the presence of close homologues of this enzyme in Enterobacter gergoviae strains, which also show a high resistance to parabens.…”