Project description:Poly(ethylene terephthalate) (PET)-degrading bacterium Ideonella sakaiensis produces hydrolytic enzymes that convert PET, via mono(2-hydroxyethyl) terephthalate (MHET), into the monomeric compounds, terephthalic acid (TPA) and ethylene glycol (EG). Understanding PET metabolism is critical if this bacterium is to be engineered for bioremediation and biorecycling. TPA uptake and catabolism in I. sakaiensis have previously been studied, but EG metabolism remains largely unexplored despite its importance. First, we identified two alcohol dehydrogenases (IsPedE and IsPedH) and one aldehyde dehydrogenase (IsPedI) in I. sakaiensis as the homologs of EG metabolic enzymes in Pseudomonas putida KT2440. IsPedE and IsPedH exhibited EG dehydrogenase activities with Ca2+ and a rare earth element (REE) Pr3+, respectively. We further found an upregulated dehydrogenase gene when the bacterium was grown on EG, whose gene product (IsXoxF) displays a minor EG dehydrogenase activity with Pr3+. IsPedE displayed a similar level of activity toward various alcohols. In contrast, IsPedH was more active toward small alcohols, whereas IsXoxF was the opposite. Structural analysis with homology models revealed that IsXoxF had a larger catalytic pocket than IsPedE and IsPedH, which could accommodate relatively bulkier substrates. Pr3+ regulated the protein expression of IsPedE negatively; IsPedH and IsXoxF were positively regulated. Taken together, these results indicated that the combination of IsPedH and IsXoxF complements the function of IsPedE in the presence of REEs. IsPedI exhibited dehydrogenase activity toward various aldehydes with the highest activity toward glycolaldehyde (GAD). This study demonstrated a unique alcohol oxidation pathway of I. sakaiensis, which could be efficient in EG utilization.
Project description:Synthetic plastics, like polyethylene terephthalate (PET), have become an essential part of modern life. Many of these products are remarkably persistent in the environment, and the accumulation in the environment is recognised as a major threat. Therefore, an increasing interest has been paid to screen for organisms able to degrade and assimilate the plastic. Ideonella sakaiensis was isolated from a plastisphere, a bacterium that solely was thriving on the degradation on PET films. The processes affected by the presence of PET, terephthalic acid, ethylene glycol, ethyl glycolate, and sodium glyoxylate monohydrate was elucidated by differential proteomes. The exposure of PET and its monomers seem to affect two major pathways, the TCA cycle and the β-oxidation pathway, since multiple of the conditions resulted in an increased expression of proteins directly or indirectly involved in these pathways, underlying the importance in the degradation of PET by I. sakaiensis.
Project description:Synthetic plastics, like polyethylene terephthalate (PET), have become an essential part of modern life. Many of these products are remarkably persistent in the environment, and the accumulation in the environment is recognised as a major threat. Therefore, an increasing interest has been paid to screen for organisms able to degrade and assimilate the plastic. Ideonella sakaiensis was isolated from a plastisphere, a bacterium that solely was thriving on the degradation on PET films. The processes affected by the presence of PET, terephthalic acid, ethylene glycol, ethyl glycolate, and sodium glyoxylate monohydrate was elucidated by differential proteomes. The exposure of PET and its monomers seem to affect two major pathways, the TCA cycle and the β-oxidation pathway, since multiple of the conditions resulted in an increased expression of proteins directly or indirectly involved in these pathways, underlying the importance in the degradation of PET by I. sakaiensis.
Project description:The accumulation of macro-, micro- and nano-plastic wastes in the environment is a major global concern, as these materials are resilient to degradation processes. However, microorganisms have evolved their own biological means to metabolize these petroleum-derived polymers, e.g., Ideonella sakaiensis has recently been found to be capable of utilizing polyethylene terephthalate (PET) as its sole carbon source. This study aims to prove its potential capacity to biodegrade two commercial PET materials, obtained from food packaging containers. Plastic pieces of different crystallinity were simultaneously introduced to Ideonella sakaiensis during a seven-week lasting investigation. Loss in weight, appearance of plastics, as well as growth of Ideonella sakaiensis-through quantitative real-time PCR-were determined. Both plastics were found enzymatically attacked in a two-stage degradation process, reaching biodegradation capacities of up to 96%. Interestingly, the transparent, high crystallinity PET was almost fully degraded first, followed by the colored low-crystallinity PET. Results of quantitative real-time PCR-based gene copy numbers were found in line with experimental results, thus underlining its potential of this method to be applied in future studies with Ideonella sakaiensis.
Project description:Polyethylene terephthalate (PET), the most abundantly produced polyester plastic, can be depolymerized by the Ideonella sakaiensis PETase enzyme. Based on multiple PETase crystal structures, the reaction has been proposed to proceed via a two-step serine hydrolase mechanism mediated by a serine-histidine-aspartate catalytic triad. To elucidate the multi-step PETase catalytic mechanism, we use transition path sampling and likelihood maximization to identify optimal reaction coordinates for the PETase enzyme. We predict that deacylation is likely rate-limiting, and the reaction coordinates for both steps include elements describing nucleophilic attack, ester bond cleavage, and the "moving-histidine" mechanism. We find that the flexibility of Trp185 promotes the reaction, providing an explanation for decreased activity observed in mutations that restrict Trp185 motion. Overall, this study uses unbiased computational approaches to reveal the detailed reaction mechanism necessary for further engineering of an important class of enzymes for plastics bioconversion.