Biopolymers were produced by cyanobacteria that capture carbon dioxide, resulting in a cheaper method that could make industrial production feasible

Biopolymers, or bioplastics, are produced from renewable sources, such as vegetable oils and manioc starch, and they can even be produced by bacteria from different substrates. One of the best-known techniques, which has been used, consists of feeding sugar to bacteria where it is metabolized by the cells and transformed into biopolymers. In a pioneering study published in Bioresource Technology magazine, researchers from the FAPESP Shell Research Centre for Gas Innovation (RCGI) discovered a new method for producing bioplastics using a cheap and abundant raw material that does not compete with the food industry: carbon dioxide (CO2).

The study made use of cyanobacteria, also know as blue-green algae, which are prokaryotic microorganisms capable of performing photosynthesis. When subjected to stress conditions in a culture medium with excessive light, cyanobacteria capture CO2 and produce poly(3-hydroxybutyrate) granules (PHB), which is a type of bioplastic. These cyanobacteria, of the genus Synechocystis sp., were gathered in mangroves around the city of Cubatão, São Paulo. “Since it is contaminated by chemical components, the microorganisms found there are extremely resistant, which is of special interest to the study,” explains Elen Aquino, who is the project coordinator and a Professor at the Federal University of São Paulo (UNIFESP).

Besides being cheaper and not competing with other markets, this method contributes to the capture and fixation one of the greenhouse gases, transforming it into an added-value product. Prof. Aquino says that 31% of the biomass produced by cyanobacteria through photosynthesis was PHB. The group also intends to perform optimization tests, under the hypothesis that it would be possible to increase production by subjecting cyanobacteria to a second stress factor, such as removing a nutrient from the medium.

In Brazil, the large-scale production of bioplastics is still a distant reality. Ms. Aquino states that there is only one company in outstate São Paulo that produces PHB with the bacterial fermentation of sugar as a carbon source. “PHB production is particularly expensive. It is a prime plastic, used mainly for manufacturing orthopedic prostheses.”

The next step in this study is to form the so-called “microbial consortium” in an attempt to enhance the production of the bioplastic: placing bacteria and cyanobacteria to grow together in a culture medium, with CO2 and CH4. Different from cyanobacteria, the bacteria utilized in another project capture methane gas (CH4) transforming it also into PHB. “Thus, we would be working with the two main greenhouse gases,” she stresses.