Bioplastic Biodegradation
- Finding The Recycling Genes -
Images of the marine bacterial community, of which the Saccharospirillum strain of this thesis was retrieved from, showing an SEM image of the control (1a, 2a) and biofilm formation and bioplastic degradation after six days (1c, 2c)1.
Introduction
An important issue that is currently concerning our world is the pollution of the oceans, rivers and soil by plastic materials that take a very long time to degrade. New materials are invented and spread, which are supposed to be biodegradable under managed, industrial conditions, called biodegradable materials2. In my bachelor thesis I have studied the genetic predispositions of a bacterial strain to degrade such biodegradable material structurally similar to PET. The complete thesis can be read here.
Abstract
This thesis deals with the genomic analysis of a binned genome from a metagenomic sample, which was retrieved from a marine bacterial community that showed the ability to degrade a biodegradable plastic material with a structure analogous to Poly(ethylene terephthalate) (PET). Experiments analyzing the consortium’s taxonomic diversity during decomposition of the material’s particular monomers proved that a bin from the metagenomic sample is capable of utilizing terephthalic acid (TPA) as sole carbon and energy source. This bin is affiliated to the genus Saccharospirillium and within this thesis compared with members of the same genus regarding their genomic foundation for degradation of the PET-like plastic material. The phylogenetic assignment revealed a close relation of the bin with the recently classified Saccharospirillium alexandrii. Both genomes share an identity of 97.7%, albeit a 16S rRNA comparison did not obtain determinative results. Two approaches for genus-wide pangenome analyses are contrasted and aim to determine the relationship between the bin and S. alexandrii further. In the Saccharospirillum genomes, a similarity-based search discovered alignments with genes known to be involved in PET degradation in Ideonella sakasiensis. Herewith gene clusters connected to TPA and phthalate degradation were detected in the binned section and S. alexandrii. An abundance profile of pathway genes is conducted, and genes associated with the degradation of aromatic hydrocarbons are mapped on the respective KEGG pathway. All observed Saccharospirillum bacteria exhibit genes connected to aromatic compound degradation, while genes incorporated at the decomposition of aromatic hydrocarbons are mainly present in S. alexandrii and bin 12. A duplication of the phthalate degradation cluster was uncovered solely in bin 12, leading to a postulate about the task assigned to Saccharospirillum bacteria in the material’s degradation process in the marine microbial consortium.
Future Prospects
♻️ I’m interested in the possibility for each person to biodegrade their used plastic at home, without depending on the poor infrastructure of the waste disposal system. First attempts can be found here.
Since most of the bacteria that can break down plastic materials live in a synergistic system with other bacteria and algae, a bioreactor that enables this habitat and additionally stores the released CO2 and converts it into O2 by photosynthesis of the algae would be an interesting approach to explore.
🧫 The fast adaptability of bacteria to novel substances when they have the genetic prerequisites to metabolize similarly structured molecules is fascinating. Novel entities, chemicals like antibiotics, are becoming a threat to our environment3, while bacteria are forming resistances to antibiotic medications. I’m interested in how these capabilities can be used in a broader context by the general public.
References
[2] European Environmental Citizens Organisation for Standardisation, European Environmental Bureau, Zero Waste Europe, Surfrider Foundation Europe, and Friends of Earth Europe. Joint position paper - Bioplastics in a Circular Economy: The need to focus on waste reduction and prevention to avoid false solutions. https://zerowasteeurope.eu/wp-content/uploads/2017/03/Joint-position-paper_Bioplastics-in-a-Circular-Economy-the-need-to-focus-on-waste-reduction-and-prevention-to-avoid-false-solutions_Jan-2017.pdf
[3] Persson, Linn, Carney Almroth, B.M., Collins, C.D. et al. Outside the Safe Operating Space of the Planetary Boundary for Novel Entities. Environmental Science & Technology 2022 56 (3), 1510-1521 https://pubs.acs.org/doi/10.1021/acs.est.1c04158