Browsing by Author "Saidu, Muhammad Bashir"
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- Exploring the biodegradation of PET in mangrove soil and its intermediates by enriched bacterial consortiaPublication . Saidu, Muhammad Bashir; Moreira, Irina S.; Amorim, Catarina L.; Wu, Rongben; Ho, Yuen-Wa; Fang, James Kar-Hei; Castro, Paula M. L.; Gonçalves, DavidThe biodegradation of Polyethylene terephthalate (PET) is important due to the environmental impact of plastic waste. This study investigates the degradation of PET films in soil microcosms, with and without mangrove plants, and with mangrove plants bioaugmented with a bacterial consortium (Bacillus sp.- GPB12 and Enterococcus sp.- WTP31B-5) while following the evolution of soil microcosm microbiome. The ability of bacterial consortia retrieved from soil microcosms of each tested condition to degrade PET intermediates - bis(2-hydroxyethyl) terephthalate (BHET), terephthalic acid (TPA), and monoethylene glycol (MEG) was also assessed. In the microcosms’ assays with mangrove plants, variations in functional groups and surface morphology detected by FTIR and SEM analysis indicated PET degradation. Soil microcosms microbiome evolved differently according to the conditions imposed, with dominance of phylum Proteobacteria in all final microcosms. After 270 days, bacterial consortia retrieved from all soil microcosms revealed to be able to completely degrade TPA within three days. MEG degradation reached ca. 84% using the consortium retrieved from the microcosm with bioaugmented mangrove plants. BHETdegradation was ca. 96% with the consortium obtained from the microcosm with non-bioaugmented mangrove plants. These intermediates are key molecules in PET degradation pathways; thus, their degradation is an indicator of biodegradation potential. To the best of authors’ knowledge, this is the first report on biodegradation of PET, BHET, TPA, and MEG by microbial community from mangrove soil, providing insights into key taxa involved in PET degradation. These findings can pave a way to develop bioremediation strategies and more efficient waste management solutions.
- Isolation and characterisation of plastic polyethylene terephthalate (PET) degrading and polyhydroxyalkanoates (PHAs) producing bacteria from soil and waterPublication . Saidu, Muhammad Bashir; Gonçalves, David Manuel Flores; Castro, Paula Maria Lima e; Moreira, Irina Susana SousaThe demand for plastic has led to enormous plastic waste in the environment, which persist and negatively impact the ecosystems. Polyethylene terephthalate (PET) is one of the most common thermoplastic polymers available on the market. The concerns about plastic waste generated an interest in strategies to enhance its biodegradation and finding alternative polymers. In this work was investigated the possibility of using bacteria to degrade PET and to produce bioplastics (Polyhydroxyalkanoates, PHAs). Finally, the integration of the two processes was tested. Overall, the work aimed to investigate the potential to recycle PET into bioplastic using bacteria. The potential of bacterial consortia from various environmental samples to degrade PET granules in liquid matrix was investigated. The results revealed maximum PET granules degradation of 1.1 % by one of the tested consortia. PET degradation intermediate terephthalic acid (TPA) was not detected at the end of 55 days. Fourier-transform infrared spectroscopy (FTIR) results showed major spectral peak shifts and bends on PET chemical structure compared to non-inoculated control. The biodegradation of PET films buried in the soil (A), with mangrove plants (B), and bioaugmented with a bacterial consortium (C) was also investigated. The experiments were conducted for 270 days at ambient conditions. The results revealed no difference between treatments in the degradation, with a maximum weight loss of 0.118 % in the bioaugmented treatment. Nevertheless, Scanning Electron Microscope (SEM) and FTIR results indicated significant surface changes, spectral peak shifts, and stretches in PET chemical structures. Bacterial consortia isolated from the soil of the experimental treatments were assessed for degradation of PET monomers, TPA and monoethylene glycol (MEG), and intermediate Bis(2-hydroxyethyl) terephthalate (BHET). The consortia were inoculated in flasks V containing minimal media with 1000 mg/L TPA or BHET or1113 mg/L MEG as the sole carbon source. Results showed complete degradation of TPA and significant degradation of BHET (96.09%), and MEG (83.65%) by the consortia. In the second part of the study, bacteria were isolated from various environmental samples and screened for PHA production using Sudan Black B staining on colonies and smeared glass slides. Transmission Electron Microscope images were captured to confirm the intracellular PHA inclusions. A total of 35 isolates were screened for PHA, and 22 showed positive staining. The isolate showing higher levels of PHA synthesis (EC2-30-3) was identified based on 16S rRNA gene sequence as Bacillus sp. and selected for PET monomers degradation and fermentation cultures for PHA production. It was cultured in minimal (Moreira et al., 2013) media with 1000 mg/L TPA and 1113 mg/L MEG as the carbon source for eight days. The isolate grew better in media containing MEG, which was selected as a substrate model for PHA fermentation. To integrate PET monomers biodegradation and production of PHA, the isolate was cultured in 0.2 % MEG. A control with 0.2 % of glucose was prepared, and the cultures were incubated for 96 hours. Bacillus sp. EC2-30-3 showed higher PHA accumulation in media supplied with MEG (40.31%) than glucose (25.53%). This is the first report showing that Bacillus sp. uses PET monomer as carbon source to produce a biopolymer. FTIR results of the extracted PHA identified its functional units as C–H, CH3, C=O, and C–O groups. The absorption bands obtained are closely related to the structure of PHB. The study thus confirmed the ability of the isolated bacteria to degrade PET monomers and produce biopolymers. The results of this work open the possibility for upscaling the use of bacteria to mitigate the impact of PET on the environment while producing environmentally friendly bioplastics.
- Mangroves as a source of polyethylene terephthalate (PET) degrading bacteriaPublication . Saidu, Muhammad Bashir; Gonçalves, David; Castro, Paula M. L.; Moreira, Irina SousaPolyethylene terephthalate (PET) is one of the most widely used plastics, and its accumulation in the environment has become an issue of great concern. PET wastes constitute a critical source of pollution to the environment, with important impacts on ecosystems and human health. One possibility to address this problem is to identify microorganisms that may be able to naturally degrade the compound for downstream applications. This study investigated the biodegradation of PET films in soil in the presence or absence of mangrove plants, and with or without bioaugmentation with bacterial isolates of the genus Bacillus and Enterococcus. The experiment was performed in an open garden for ten months. At the end of this period, biodegradation assays of PET monomers and intermediate were further performed using bacterial consortia isolated from the soil of the different treatments. Terephthalic acid (TPA) and bis-2-hydroxyethyl terephthalate (BHET) were added to liquid medium as the sole carbon sources and incubated for 10 days at 30oC. Growth of the consortia was monitored by spectrophotometry, and degradation was followed by HPLC analysis of aliquot samples. The preliminary results from gravimetry analysis showed no significant changes in PET films, regardless of the treatment. On the other hand, total degradation of TPA and BHET was observed for all assays independently of treatment. The results suggest that although direct biodegradation of PET may be challenging to accomplish, bacteria capable of degrading the intermediates and monomers of PET are readily available in the natural environment.