Exploring CO2 as feedstock for production of biopolymers by the bacteria Chloroflexus aurantiacus

• Autor(a) principal: Diamantino, Rodrigo Miguel Folgado
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/160306
• topic: Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

With CO2 and plastic waste rising globally, developing a method that allows CO2 capture and its transformation into biodegradable polymers is an appealing prospect. One organism capable of such feature is Chloroflexus aurantiacus, a filamentous anoxygenic bacteria that presents a very versatile metabolism. This extremophile is capable of using solar energy for CO2 fixation and adverse components as electron donors (e.g., hydrogen sulphide), to produce polyhydroxyalkanoates (PHA) and accumulate them as internal reserves. PHAs are microbially synthesized polyesters that offer a wide range of properties, similar to petrochemical plastics, yet are fully biobased, biodegradable, and more biocompatible than conventional polymers. In this work we plan to outlay a possible alternative to the conventional methods of PHA production, using CO2 capture and hydrogen sulphide removal by C. aurantiacus Y-400-fl (DSM 637) to provide a path for a sustainable and inexpensive PHA production process. Hopefully, this work will contribute to lower PHA production costs, and thus make it viable for new markets. In this work the growth of C. aurantiacus Y-400-fl (DSM 637) was optimized in lab conditions, analysing its response to variations in the culture medium composition, which impacted the overall behaviour of the organism and its polymer production, both in quantity and monomeric composition of the PHA produced. In the course of this thesis C. aurantiacus Y-400-fl (DSM 637) was grown under several different media, with different carbon sources (glycylglycine, glycine and sodium carbonate), sulphide concentrations from 0.078 mM to 0.625 mM and with light intensities from 0.58 to 4.4 W/l. The results showed that C. aurantiacus Y-400-fl (DSM 637) has an ideal sulphide concentration of around 0.313 mM when waking up and maintaining growth using organic carbon sources (glycylglycine), that it is a fast adapting organism, that shows similar growth profiles regardless of whether its inoculum was grown under a low or high light intensity, that the bacteria is able to assimilate inorganic carbon (Na2CO3) and grow normally without the presence of glycylglycine, and that under organic carbon conditions it’s possible to replace the expensive glycylglycine with glycine, without affecting the organism’s growth profile. Grown under anaerobic conditions with continuous illumination, C. aurantiacus Y-400-fl (DSM 637), was able to achieve 15% PHA content per cell dry weight when fed with an organic carbon substrate (glycylglycine). Preliminary tests to evaluate C. aurantiacus growth on inorganic carbon-based medium resulted in low PHA content, indicating the importance of future tests to target operation under ideal accumulation conditions (e.g., nutrient limitation, adjusted sulphide concentrations.