Evaluating the PHA storage capacity and the impacts of growth conditions on Chloroflexus aurantiacus, a green non-sulphur phototrophic bacterium

The CO2 global average concentration has grown at an alarming rate in the last decade reaching 413 ppm in July 2021, positioning as the primary driver of climate change. The production of the major plastic materials globally produced still rely on fossil fuels, contributing to the release of CO2 in the atmosphere. It is in this contest, that bioplastic industry, particularly PHAs production brings many ecological advantages. PHAs are microbial synthetized polyesters polymers which are both biobased and biodegradable. They are versatile materials, whose properties, hence their applications, depend on their monomer composition, molecular weight and microstructure. This work proposed a more cost-effective and novelty approach, analysing the possibility to produce PHAs by C. aurantiacus, a photosynthetic non-sulphur green bacterium, which has a highly metabolic versatility. In fact, C. aurantiacus can grow in aerobic and anaerobic conditions, heterotrophically with several organic sources and autotrophically with CO2 only as the sole carbon. This was an exploratory work with the aim to evaluate the bacterium capacity to accumulate PHA under anaerobic conditions. Furthermore, new methodologies needed to be implemented and basic operating conditions were tested such as the inoculum-medium ratio, the correlation between OD and cdw and the state of the inoculum. Its growth was first characterized in a rich medium with glycyl-glycine and sulphide, different light intensities and temperatures. Meanwhile, it was possible to evaluate different media impact on its growth, PHA accumulating capacity and pigment synthesis, observing promising results from inorganic media and mixotrophic growth. Moreover, new microorganisms have been isolated from phototrophic mixed culture bioreactor to enlarge the laboratory library of phototrophic microorganisms capable of producing PHAs from inorganic carbon source, revealing an almond-shape purple bacteria able to accumulate PHA.