Evaluation of polyester polyurethane-degrading capability of bacteria isolated from landfill sites

References

1. 1 3276 N-H stretching vibration of urethane 28-30 2,3 2976, and 2864 CH2 stretching vibrations 29-33 4 1727 C=O stretching vibration of free urethane 28, 29,34,35 5 1640 C=O stretching vibration of amides 30 6 1600 C=O hydrogen in urethane 36 7 1537 N-H bending vibration of urethane 29, 30, 34,37,38 8 1375 CH2 and CH3 in carbon backbone 35 9 1222 C-N stretching vibration of urethane 11, 28 10 1085 C-O stretching in C-O-C=O of urethane 29,30,33
2. Scanning electron microscopy (SEM) analysis Scanning Electron Microscopy (SEM) was used to assess the morphological modifications on the surface of the PU cubes. This technique enables a qualitative evaluation of surface degradation after biological treatment by observing cracks or holes on the degraded polymers. SEM images of the PU foam in NB, and inoculated NB are presented in Figure 6. Figure 6: Scanning electron microscopy view (×50, 250, and 500 magnification) of the PU foam immersed in NB, and inoculated NB after three months of incubation at 37℃, with shaking for 30 minutes/day
3. Discussion Bacillus velezensis is an aerobic, Gram-positive, endospore- forming, and free-living soil bacterium first described by Ruiz-Garcia et al., 2005. 39 In recent years, the bacterium has gained scientific interest as a potential biocontrol agent against phytopathogens, and as a microbial inhibitor. It also shows potential for food preservation due to its ability to produce antimicrobials, volatile organic compounds, bioactive enzymes, and plant growth -promoting substances. 40-42 Moreover, Bacillus velezensis exhibits promising probiotic properties, including high bile salt tolerance, absence of antibiotic resistance and virulence factors, and a high success rate of colonization in the intestinal mucosa. Additionally, it demonstrates the ability to degrade mycotoxins such as zearalenone. 43 Additionally, the ability to form endospores is a significant advantage for Bacillus velezensis, allowing it to survive in unfavorable environments, such as high temperatures, desication, and exposure to gastric juices. A study conducted by Gui Z et al., 6 demonstrated that Bacillus velezensis GUIA, isolated from a deep-sea environments, is capable of degrading waterborne polyurethane (Impranil), with the oxidoreductase Oxr-1 identified as the key enzyme responsible for degradation. Zeng et al., 44 reported that Bacillus velezensis MB01B, isolated from landfill soil, can degrade commercial PUR materials, including Impranil, TPU film and PUR desk mats. Bacillus velezensis D 3.2.1 and M 1.2.1 have the ability of degrading Impranil stronger than other bacteria in some previous studies. 45,46 Changes of chemical groups durin g plastic biodegradation can provide insight into which part of the polymer molecule is being degraded. Polyester polyurethane contains both urethane and ester bonds within its molecular structure, so degradation occurs primarily through the cleavage of these bonds. Several studies have reported a decrease in the abundance of carbonyl groups detected by FTIR, indicating that the degradation predominantly affects Nguyen et al. / Indian Journal of Microbiology Research 2025;12(3):364–371 369 the soft segments of the polymer. 16,26,38,47 Consistent with this observation, the functional groups within the frequency range of 1730 cm -1 to 1000 cm -1 shows significant changes in this work. The FTIR spectrum of the orginal Impranil has a large absorption peak at 1730 cm -1 related to C=O stretch in the ester fraction. 38,46,48 A complete loss of this peak is observed in the FTIR spectra of inoculated NB containing 1% or 3% Impranil. This result indicates the hydrolysis of the ester bond in the urethane linkage. This finding aligns with the results reported in other studies. 8,38,49,52 A sharp increase in the peak at 1530 cm -1 , which is typically attributed to the nitrogen of the urethane moieties, is clearly observed in both 1% and 3% Impranil samples. According to Oprea, 53 an increase in this peak is associated with urethane bond hydrolysis. However, other studies have suggested that a decrease in this peak results from urethane bond degradation. 10,33,49,54,55 A sharp increase in the peak at 1400 cm -1 , associated with the CH2 bond, is clearly observed in FTIR spectra. 56,57 This observation aligns with the study conducted by Nakkabi et al., 46 on the biodegradation of polyester polyurethanes by Bacillus subtilis. In addressing the degradation of PU, the cleavage of the urethane bond appears to be a key factor. A decrease in the band at 1240 cm -1 , corresponding to the C-O- C elongation vibration of the urethane group, is observed in the sample supplemented with 1% Impranil. 16,49,50 A reduced intensity of the peaks around 1140 cm -1 and 1170 cm -1 , corresponding to C-O stretching, indicates a change in the ester component. 8,20,54 The results show that both the ester and urethane components in Impranil structure are degraded by the strain D 3.2.1 isolated from soil in a plastic landfill. Evaluating PU foam degradation is much more challenging than Impranil, as the substrate is a highly complex system based on crosslinked architectures with various components and additives. Thanks to its alveolar structure, microorganisms can easily attach to, colonize the surface of PU foam, initiating microbial biodegradation. In most plastic degradation studies, solid substrates are generally pre-treated with UV irradiation, thermal and chemical treatments to modify the polymers and facilitate the plastic degradation by microorganisms. 2,58 However, the PU foam used in this work was not subjected to any pretreatments, such as physical and chemical agents, to alter its structural and morphological characteristics and facilitate microbial degradation. Therefore, the time during which the PU substrate was immersed in the culture medium inoculated with the bacterium needs to be longer to obtain chemical and physical changes as indicators of the biodegradation process. The strain D 3.2.1 was isolated from landfill soil. Microbial biodegradation of PU plastics is primarily mediated by the enzymatic action of hydrolases, including esterases, ureases, proteases, and amidases. Esterases hydrolyze the ester bonds in the soft segment of polyester-based PU plastics, resulting in the release of carboxylic acid and alcohol end-groups. Ureases are capable of degrading urethane bonds in selected polyurea-urethane polymer, releasing two amines and carbon dioxide. Proteases and amidases are two additional enzymes involved in PU degradation, these enzymes hydrolyze peptide or amide bonds and have also been reported to attack urethane bonds. 7,20,27,59-61 One of the major challenges in the enzymatic degradation of PU is that only the ester bonds in the soft segments of polyester-based PU are typically hydrolyzed, with few reports on the biodegradation of urethane bonds. 26 In the study, the FTIR results from PU foam indicate that the urethane components (the peak at 1085 cm -1 ) were degraded by the strain D 3.2.1 isolated from soil after three months of incubation in NB. The finding is consistent with the study led by Orts et al. 11 The fibrous structure of the PU foam facilitates the attachment and colonization of the bacterium on the substrate, thereby enhancing the biodegradation rate. However, this structure makes it relatively difficult to observe morphological changes in the SEM images. The fiber density of the PU foam in inoculated NB appears to be lower than that of the foam immersed in NB. Based on the FTIR analysis, the biodegradation process in the experimental lot has only just begun after three months of incubation at 37℃. Consequently, significant morphological changes in the PU foam may not be clearly visible yet.
4. Conclusion The bacterial strain (Bacillus velezensis D 3.2.1), isolated from landfill soil, was evaluated for its polyester polyurethane-degrading activity. FTIR analysis confirms that this strain is capable of degrading ester and urethane bonds in a liquid substrate (Impranil). On a solid substrate (PU foam), only urethane component was attacked by the bacterial strain. These findings highlight the potential use of microorganisms isolated from natural environments for polyester polyurethane degradation, offering a promising alternative to mitigate the global plastic crisis. However, further research is needed to identify the key enzymes involved in polyester polyurethane degradation and to optimize enzymatic conditions for industrial-scale applications.
5. Source of Funding This research was financially supported by the Nong Lam University - Ho Chi Minh City research funding (the research code: CS-CB23-CNTY-02).
6. Conflict of Interest The authors declare no conflict of interest with the present study.
7. Data Availability Statement The data that support the findings of this study are available from the corresponding author upon reasonable request. References
8. Chalmin P. The history of plastics: from the Capitol to the Tarpeian Rock. Field Actions Sci Rep. 2019;(Spec Issue 19):6–11. 370 Nguyen et al. / Indian Journal of Microbiology Research 2025;12(3):364–371
9. Crystal Thew XE, Lo SC, Ramanan RN, Tey BT, Nguyen DH, Wei OC. Enhancing plastic biodegradation process: strategies and opportunities. Crit Rev Biotechnol. 2023;44(3):477–94.
10. Kumar L. A review on biodegradation of post-production and post- consumer polyurethane wastes. Int J Adv Multidiscip Res. 2002;9(5):110–25.
11. Ritchie H. How much of global greenhouse gas emissions come from plastics [Internet]. OurWorldinData.org; 2023. Available from: https://ourworldindata.org/ghg-emissions-plastics.
12. Brunner I, Fischer M, Rüthi J, Stierli B, Frey B. Ability of fungi isolated from plastic debris floating in the shoreline of a lake to degrade plastics. PLoS One. 2018;13(8):e0202047.
13. Gui Z, Liu G, Liu X, Cai R, Liu R, Sun C. A deep-sea bacterium is capable of degrading Polyurethane. Microbiol Spectr. 2023;11(3):e0007323.
14. Howard GT, Norton WN, Burks T. Growth of Acinetobacter gerneri P7 on polyurethane and the purification and characterization of a polyurethanase enzyme. Biodegradation. 2021; 23(4):561–73.
15. Kim JH, Choi SH, Park MG, Park DH, Son KH, Park HY. Polyurethane biodegradation by Serratia sp. HY-72 isolated from the intestine of the Asian mantis Hierodula patellifera. Front Microbiol. 2022;13:1005415.
16. Mukherjee K, Tribedi P, Chowdhury A, Ray T, Joardar A, Giri S, et al. Isolation of a Pseudomonas aeruginosa strain from soil that can degrade polyurethane diol. Biodegradation. 2011;22(2):377–88.
17. Oceguera-Cervantes A, Carrillo-García A, López N, Bolaños-Nuñez S, Cruz-Gómez MJ, Wacher C, et al. Characterization of the polyurethanolytic activity of two Alicycliphilus sp. strains able to degrade polyurethane and N-methylpyrrolidone. Appl Environ Microbiol. 2007;73(19):6214–23.
18. Orts JM, Parrado J, Pascual JA, Orts A, Cuartero J, Tejada M, et al. Polyurethane foam residue biodegradation through the Tenebrio molitor digestive tract: microbial communities and enzymatic activity. Polymers. 2023;15(1):204.
19. Salgado CA, Silva JG, Almeida FA, Vanetti MCD. Biodegradation of polyurethanes by Serratia liquefaciens L135 and its polyurethanase: in silico and in vitro analyses. Environ Pollut. 2023;333:122016.
20. Kemona A, Piotrowska M. Polyurethane recycling and disposal: methods and prospects. Polymers. 2020;12(8):1752.
21. de Souza FM, Kahol PK, Gupta RK. Introduction to polyurethane chemistry. In: Polyurethane chemistry: Renewable polyols and isocyanates. American Chemical Society; 2021. pp. 1-24.
22. Maestri C, Plancher L, Duthoit A, Hébert RL, Di Martino P. Fungal biodegradation of polyurethanes. J Fungi. 2023;9(7):760.
23. Rajan A, Ameen F, Jambulingam R, Shankar V. Biodegradation of polyurethane by fungi isolated from industrial wastewater—a sustainable approach to plastic waste management. Polymers. 2024;16(10):1411.
24. Russell JR, Huang J, Anand P, Kucera K, Sandoval AG, Dantzler KW, et al. Biodegradation of polyester polyurethane by endophytic fungi. Appl Environ Microbiol. 2011;77(17):6076–84.
25. Wu KY, Yang TX, Yang M, Wu JQ, Li X, Chen XD, et al. Preliminary identification of soil fungi for the degradation of polyurethane film. Arch Microbiol. 2023;205(4):145.
26. Peng YH, Shih YH, Lai YC, Liu YZ, Liu YT, Lin NC. Degradation of polyurethane by bacterium isolated from soil and assessment of polyurethanolytic activity of a Pseudomonas putida strain. Environ Sci Pollut Res Int. 2014;21(16):9529–37.
27. Schmidt J, Wei R, Oeser T, Dedavid E Silva LA, Breite D, Schulze A, et al. Degradation of polyester polyurethane by bacterial polyester hydrolases. Polymers (Basel). 2017;9(2):65.
28. Shah Z, Krumholz L, Aktas DF, Hasan F, Khattak M, Shah AA. Degradation of polyester polyurethane by a newly isolated soil bacterium, Bacillus subtilis strain MZA-75. Biodegradation. 2013;24(6):865–77.
29. Rowe L, Howard GT. Growth of Bacillus subtilis on polyurethane and the purification and characterization of a polyurethanase-lipase enzyme. Int Biodeterior Biodegradation. 2002;50(1):33–40.
30. Yazhini VS, Prabha ML, Issac R. Characterization and molecular identification of poly urethane degrading bacteria. J Pure Appl Microbiol. 2021;15(3):1291–300.
31. Zarezadeh E, Tangestani M, Jafari AJ. A systematic review of methodologies and solution for recycling polyurethane foams to safeguard environment. Heliyon. 2024;10:e40724.
32. Marchesi JR, Sato T, Weightman AJ, Martin TA, Fry JC, Hiom SJ, et al. Design and evaluation of useful bacterium-specific PCR primers that amplify genes coding for bacterial 16S rRNA. Appl Environ Microbiol. 1998;64(2):795–9.
33. Biffinger JC, Barlow DE, Pirlo RK, Babson DM, Fitzgerald LA, Zingarelli S, et al. A direct quantitative agar-plate based assay for analysis of Pseudomonas protegens Pf-5 degradation of polyurethane films. Int Biodeterior Biodegradation. 2014;95(Pt B):311–9.
34. Liu J, He J, Xue R, Xu B, Qian X, Xin F, et al. Biodegradation and up-cycling of polyurethanes: progress, challenges, and prospects. Biotechnol Adv. 2021;48:107730.
35. Dulyanska Y, Cruz-Lopes L, Esteves B, Guiné R, Domingos I. FTIR monitoring of polyurethane foams derived from acid-liquefied and base-liquefied polyols. Polymers. 2024;16(15):2214.
36. Francés AB, Banon MVN. Effect of silica nanoparticles on polyurethane foaming process and foam properties. In: IOP Conference Series: Materials Science and Engineering. Bristol, UK: IOP Publishing; 2014. p. 012020.
37. Smith BC. Infrared spectroscopy of polymers XIII: polyurethanes. Spectroscopy. 2023;38(7):14–6.
38. Mora-Murillo LD, Orozco-Gutierrez F, Vega-Baudrit J, González- Paz RJ. Thermal-mechanical characterization of polyurethane rigid foams: effect of modifying bio-polyol content in isocyanate prepolymers. J Renew Mater. 2017;5(3-4):220–30.
39. Paberza A, Fridrihsone-Girone A, Abolins A, Cabulis U. Polyols from recycled poly(ethylene terephthalate) flakes and rapeseed oil for polyurethane foams. Polimery. 2015;60(9):572–8.
40. Plancher L, Nguyen GTM, Hébert R, Maestri C, Mélinge Y, Ledésert B, et al. Oxidative biodegradation of a solid-solid polyether-urethane phase change material by Penicillium and Aspergillus. Mater Today Commun. 2021;29:102949.
41. Beneš H, Černá R, Ďuračková A, Petra L. Utilization of natural oils for decomposition of polyurethanes. J Polym Environ. 2012;20(1):175–85.
42. Wärnheim A, Kotov N, Dobryden I, Leggieri RT, Edvinsson C, Heydari G, et al. Nanomechanical and nano-FTIR analysis of polyester coil coatings before and after artificial weathering experiments. Prog Org Coat. 2024;190:108355.
43. Neswati, Nazir N, Arief S, Yusniwati. Improvement of flexible polyurethane foam characteristics of palm oil polyols with the addition of polyethylene glycol 400. In: IOP Conference Series: Earth and Environmental Science. Bristol, UK: IOP Publishing;
44. p. 012031.
45. Członka S, Strąkowska A, Kairytė A. Application of walnut shells- derived biopolyol in the synthesis of rigid polyurethane foams. Materials (Basel). 2020;13(12):2687.
46. Su T, Zhang T, Liu P, Bian J, Zheng Y, Yuan Y, et al. Biodegradation of polyurethane by the microbial consortia enriched from landfill. Appl Microbiol Biotechnol. 2023;107(5-6):1983–95.
47. Ruiz-García C, Béjar V, Martínez-Checa F, Llamas I, Quesada E. Bacillus velezensis sp. nov., a surfactant-producing bacterium isolated from the river Vélez in Málaga, southern Spain. Int J Syst Evol Microbiol. 2005;55(Pt 1):191–5.
48. Byun H, Brockett MR, Pu Q, Hrycko AJ, Beld J, Zhu J. An intestinal Bacillus velezensis isolate displays broad-spectrum antibacterial activity and prevents infection of both Gram-Positive and Gram- Negative pathogens in vivo. J Bacteriol. 2023;205(6):e0013323.
49. Liu H, Jiang J, An M, Li B, Xie Y, Xu C, et al. Bacillus velezensis SYL-3 suppresses Alternaria alternata and tobacco mosaic virus infecting Nicotiana tabacum by regulating the phyllosphere microbial community. Front Microbiol. 2022;13:840318. Nguyen et al. / Indian Journal of Microbiology Research 2025;12(3):364–371 371
50. Su T, Shen B, Hu X, Teng Y, Weng P, Wu Z, et al. Research advance of Bacillus velezensis: bioinformatics, characteristics, and applications. Food Sci Hum Wellness. 2024;13(4):1756–66.
51. Li Y, Chen S, Yu Z, Yao J, Jia Y, Liao C, et al. A novel Bacillus velezensis for efficient degradation of zearalenone. Foods. 2024;13(4):530.
52. Zeng J, Yao J, Zhang W, Zhang M, Wang T, Yu X, et al. Biodegradation of commercial polyester polyurethane by a soil- borne bacterium Bacillus velezensis MB01B: efficiency, degradation pathway, and in-situ remediation in landfill soil. Environ Pollut. 2024;363(Pt 2):125300.
53. Liu J, Zeng Q, Lei H, Xin K, Xu A, Wei R, et al. Biodegradation of polyester polyurethane by Cladosporium sp. P7: evaluating its degradation capacity and metabolic pathways. J Hazard Mater. 2023;448:130776.
54. Nakkabi A, Moulay Sadiki M, Fahim M, Najim Ittobane N, IbnsoudaKoraichi S, Barkai H, et al. Biodegradation of poly(ester urethane)s by Bacillus subtilis. Int J Environ Res. 2015;9(1):157–
55. Magami S, Akimoto H. The degradation mechanism of high- strength polyurethane elastomers in the presence of water. Komatsu Tech Rep. 2023;69(176):26–33.
56. Singhal P, Small W, Cosgriff-Hernandez E, Maitland DJ, Wilson TS. Low density biodegradable shape memory polyurethane foams for embolic biomedical applications. Acta Biomater. 2014;10(1):67–76.
57. Álvarez-Barragán J, Domínguez-Malfavón L, Vargas-Suárez M, González-Hernández R, Aguilar-Osorio G, Loza-Tavera H. Biodegradative activities of selected environmental fungi on a polyester polyurethane varnish and polyether polyurethane foams. Appl Environ Microbiol. 2016;82(17):5225–35.
58. De Smet D, Verjans J, Bader M, Mondschein A, Vanneste M. Design of biodegradable PU textile coating. Polymers. 2024;16(16):2236.
59. Nakkabi A, Ittobane N, Dary M, Duran EM, Fahim M. Growth of Pseudomonas in polyurethane medium. IOSR J Eng. 2015;5(7):36–
60. Nakkabi A, Sadiki M, Ibnssouda S, Fahim M. Biological degradation of polyurethane by a newly isolated wood bacterium. Int J Recent Adv Multidiscip Res. 2015;2(2):222–5.
61. Oprea S. Dependence of fungal biodegradation of PEG/castor oil- based polyurethane elastomers on the hard-segment structure. Polym Degrad Stab. 2010;95(12):2396–404.
62. Frautschi JR, Chinn JA, Phillips RE, Zhao QH, Anderson JM, Joshi R, et al. Degradation of polyurethanes in vitro and in vivo: comparison of different models. Colloids Surf B Biointerfaces. 1993;1(5):305–13.
63. Sarkar D, Lopina ST. Oxidative and enzymatic degradations of l- tyrosine based polyurethanes. Polym Degrad Stab . 2007;92(11):1994–2004.
64. Fuentes-Jaime J, Vargas-Suárez M, Cruz-Gómez MJ, Loza-Tavera H. Concerted action of extracellular and cytoplasmic esterase and urethane-cleaving activities during Impranil biodegradation by Alicycliphilus denitrificans BQ1. Biodegradation. 2022;33(4):389–
65. Magaña-Montiel N, Muriel-Millán LF, Pardo-López L. XTT assay for detection of bacterial metabolic activity in water-based polyester polyurethane. PLoS One. 2024;19(6):e0303210.
66. Park WJ, Hwangbo M, Chu KH. Plastisphere and microorganisms involved in polyurethane biodegradation. Sci Total Environ. 2023;886:163932.
67. Cai Z, Li M, Zhu Z, Wang X, Huang Y, Li T, et al. Biological degradation of plastics and microplastics: a recent perspective on associated mechanisms and influencing factors. Microorganisms. 2023;11(7):1661.
68. Magnin A, Pollet E, Phalip V, Avérous L. Evaluation of biological degradation of polyurethanes. Biotechnol Adv. 2020;39:107457.
69. Magnin A, Pollet E, Perrin R, Ullmann C, Persillon C, Phalip V, et al. Enzymatic recycling of thermoplastic polyurethanes: synergistic effect of an esterase and an amidase and recovery of building blocks. Waste Manag. 2019;85:141–50. Cite this article: Nguyen XNT, Lu NNT, Vo TVH, Nguyen HN. Evaluation of polyester polyurethane-degrading capability of bacteria isolated from landfill sites. Indian J Microbiol Res. 2025;12(3):364–371.