Samenvatting
Petroleum-based conventional plastics are essential materials in our daily lives. However, despite their importance, their production and end-of-life fates negatively affect our environment. Polyhydroxyalkanoates (PHA) are one of the most promising solutions to solve this dilemma, as they are microbially produced biobased and biodegradable polymers that can act as a green alternative to conventional plastics. The physicochemical features of PHAs are comparable to polypropylene. They are produced by diverse prokaryotes in response to nutritional or environmental stress conditions and stored as intracellular granules.
Regardless of the interesting features of PHAs, high production costs currently stand as an obstacle that hinders their large-scale production and commercialization. The use of thermophiles, microorganisms growing optimally at high temperature ranges, for PHA production can help in improving cost efficiency on an industrial scale. This is achieved by lowered operational costs of cooling and sterilization.
In this PhD study, I delved into the ability of thermophiles to synthesize and accumulate PHAs,7 thereby exploring the underlying genetic machinery. Several thermophilic bacterial strains were selected for investigation, encompassing a wide temperature range. Their abilities to accumulate PHAs in response to different nutritional and stress conditions were studied. Five approaches of analysis were employed to unveil the PHA production potential and machinery
of thermophiles throughout this study: bioinformatics analysis, growth analysis, chemical analysis of the extracted PHA polymers, proteomic analysis of PHA granules-attached proteins and transcriptomic analysis upon growth in different nutritional growth media to study the metabolic fluxes in these conditions.
The results pointed to the presence of a harsh temperature limit above which the PHA accumulation ability becomes very scarce to almost absent in extreme thermophiles and hyperthermophiles. In contrast, at lower temperature ranges I described a novel thermotolerant PHA producer, Paracoccus kondratievae (42-47°C), to produce poly-3-hydroxybutyrate upon growth on glycerol. In addition, the moderate thermophilic bacterium Caldimonas thermodepolymerans (50-55°C) was found to be able to accumulate PHA copolymers with enhanced physical properties upon changing growth conditions. A tight interconnected relation was observed between the exposure to stress conditions, gene regulation and PHA production.
In conclusion, this PhD work succeeded in shedding light on the ability of thermophiles to biosynthesize PHAs, and in this way, it can be considered as an important step in paving the way to utilize thermophilic strains as microbial cell factories for PHA production.
Regardless of the interesting features of PHAs, high production costs currently stand as an obstacle that hinders their large-scale production and commercialization. The use of thermophiles, microorganisms growing optimally at high temperature ranges, for PHA production can help in improving cost efficiency on an industrial scale. This is achieved by lowered operational costs of cooling and sterilization.
In this PhD study, I delved into the ability of thermophiles to synthesize and accumulate PHAs,7 thereby exploring the underlying genetic machinery. Several thermophilic bacterial strains were selected for investigation, encompassing a wide temperature range. Their abilities to accumulate PHAs in response to different nutritional and stress conditions were studied. Five approaches of analysis were employed to unveil the PHA production potential and machinery
of thermophiles throughout this study: bioinformatics analysis, growth analysis, chemical analysis of the extracted PHA polymers, proteomic analysis of PHA granules-attached proteins and transcriptomic analysis upon growth in different nutritional growth media to study the metabolic fluxes in these conditions.
The results pointed to the presence of a harsh temperature limit above which the PHA accumulation ability becomes very scarce to almost absent in extreme thermophiles and hyperthermophiles. In contrast, at lower temperature ranges I described a novel thermotolerant PHA producer, Paracoccus kondratievae (42-47°C), to produce poly-3-hydroxybutyrate upon growth on glycerol. In addition, the moderate thermophilic bacterium Caldimonas thermodepolymerans (50-55°C) was found to be able to accumulate PHA copolymers with enhanced physical properties upon changing growth conditions. A tight interconnected relation was observed between the exposure to stress conditions, gene regulation and PHA production.
In conclusion, this PhD work succeeded in shedding light on the ability of thermophiles to biosynthesize PHAs, and in this way, it can be considered as an important step in paving the way to utilize thermophilic strains as microbial cell factories for PHA production.
| Originele taal-2 | English |
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| Toekennende instantie |
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| Begeleider(s)/adviseur |
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| Datum van toekenning | 3 jul 2024 |
| Uitgever | |
| Gedrukte ISBN's | 9789464948325 |
| Status | Published - 2024 |