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Evolutionary engineering of Geobacillus thermoleovorans for growth on adipic acid and 1,4-butanediol.
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Researchers used adaptive laboratory evolution to engineer the thermophile Geobacillus thermoleovorans to grow robustly on adipic acid and 1,4-butanediol — monomers released from the biodegradable plastic PBAT — and demonstrated that co-cultivating the evolved strains with a cutinase enables direct plastic upcycling at elevated temperatures, with genomic and transcriptomic analysis revealing the responsible metabolic pathways.
The plastic pollution crisis urges innovative recycling solutions. Promising approaches especially for polyester-containing wastes include enzymatic hydrolysis and microbial upcycling. For efficient enzymatic hydrolysis of polyesters, elevated temperatures (70-80 °C) are required, necessitating thermophilic microbial chassis for consolidated bioprocessing (CBP). In this study, we engineered Geobacillus thermoleovorans through adaptive laboratory evolution (ALE) for robust growth on adipic acid (AA) and 1,4-butanediol (BDO), two relevant monomers for example derived from poly(butylene adipate-co-terephthalate) (PBAT), enabling growth rates of up to 0.10 h on AA and 0.13 h on BDO. Based on a high-quality annotated genome sequence of the wild type, genomic mutations and gene expression levels were characterized in mutants grown on the respective substrates compared to glucose. For BDO, an alcohol dehydrogenase (Gth_001044) and an aldehyde dehydrogenase (Gth_001082) were identified to be likely responsible for its oxidative degradation. AA uptake appears to be mediated by a dicarboxylate transporter (Gth_003270), followed by CoA activation and β-oxidation involving a CoA transferase (Gth_003192) and several upregulated CoA-family dehydrogenases. To demonstrate applicability of these strains in plastic upcycling, they were co-cultivated with PBAT as the sole carbon source in combination with the cutinase HiC for PBAT hydrolysis. This resulted in growth on the released AA and BDO. Given the potential to purify the remaining terephthalate (TA), this approach highlights the feasibility of selective monomer valorization in bioprocesses. Additional ALE enabled co-utilization of AA and BDO by a single strain and improved AA consumption at lower concentrations, underscoring the strains' adaptability and high potential for plastic upcycling applications. KEY POINTS: • G. thermoleovorans evolved for robust growth on adipate and 1,4-butanediol at 60 °C. • Genome and transcriptome analyses revealed underlying pathways and enzymes involved. • Co-cultivation of the evolved strains on PBAT with HiC as the sole carbon source.
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