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Polyethylene terephthalate (PET) plastic is the most widely used type of plastic that produces waste and causes various environmental and health problems. The treatment of PET plastic waste with chemically and mechanically recycling approaches still has shortcomings, so biological processing using microorganisms or enzymes has new potential. Two bacterial isolates from the Indonesian Culture Collection of National Research and Innovation Agency (InaCC, BRIN), namely isolate InaCC B538 and InaCC B947, were further observed for their potential in PET plastic degradation. Firstly, both isolates were determined by the molecular marker 16S rDNA. The potential of both isolates was measured with following method: 10 days of degradation using PET and PCL substrates, esterase enzyme activity assay, and observation of the PET plastic surface using Scanning Electron Microscope (SEM). Species identification was performed using DNA sequencing of 16S rDNA. InaCC B538 and InaCC B947 were closely related to Bacillus altitudinis TBMAX41 and Alcaligenes faecalis AN-13, respectively. InaCC B947 isolate has a better potential in degrading PET plastic and PCL with a degradation percentage of 0.32% for PET plastic and 3.22% for PCL film for 10 days, respectively, and esterase activity of 0.06 U/ml; while InaCC B538 did not cause weight loss of PET and 2.49% for PCL, respectively, with esterase activity of 0.04 U/ml. The degradation of PET plastic by the isolates InaCC B947 was able to cause damage to the plastic surface leading to the degradation of PET plastic.

Protein structure has a direct impact on thermostability. Deviations in the primary sequence can affect structural changes, leading to alterations in thermostability properties. However, the molecular basis of protein thermostability is unspecified; thus, elucidation of key factors that role particular protein thermostability is required when engineering proteins to be thermostable. To address this challenge, the amino acid composition, hydrophobicity/hydrophilicity ratio, cysteine bridges, and intrinsic features of two structurally homologous but different thermostability, poly(ethylene terephthalate) hydrolase (PETase) were compared. According to the findings, thermostable and thermolabile PETases have similar folds, compactness, and disulfide bridges. Interestingly, an abundance gap of aromaticity, hydrophobic cluster area, polar amino acid and hydrogen bond network compositions demonstrated dominant trends of variations for both PET hydrolases, indicating a pivotal role of these features in the thermostability of PET hydrolase. Furthermore, increased hydrophobic amino acid frequency in the inner surface of thermostable proteins contributed significantly to thermostability by forming more internal hydrophobic interactions and a less hydrophobic patch. There are no consistent trends in insertions and deletions between both PETases. Taken together, these observations demonstrate that hydrophobicity and hydrogen bond networks are essential factors in thermostability of thermostable PETase.