Polyhydroxyalkanoates: Biosynthesis Optimization and Design of Antimicrobial Composites

Abstract

Background. The accumulation of plastic waste negatively affects the environment and human health. Currently, one of the strategies to address this global ecological problem involves the utilization of biodegradable plastics instead in place of synthetic ones. Among them, polyhydroxyalkanoates (PHA) – microbial intracellular polymers – hold a significant position. Their advantages are biodegradability, biocompatibility, and favorable thermomechanical properties. Given these attributes, PHA has significant prospects for use in medicine, agriculture, and the food industry, in particular for packaging food products. Objective. Enchance the efficiency of bacterial synthesis of polyhydroxyalkanoates through nutrient media modification, obtain antimicrobial composites based on PHA, and determine their antimicrobial properties. Methods. The optimization of PHA biosynthesis involved selecting appropriate cultivation conditions, including carbon and nitrogen sources, cultivation time, and working volume. The isolation of PHA from bacterial biomass was achieved through chloroform extraction (mixing for 10 h at 35 °C, with a biomass-to-chloroform ratio of 1:50); followed by precipitation with double the volume of isopropanol. The resulting polymer was then dried to a constant weight at 60 °C. The hydrophobicity of the biopolymer was assessed using the water contact angle measurement. Composites of biopolymers with antimicrobials in the form of films were obtained using two methods: 1) solution casting method; and 2) layering the biocides onto the polymer film. The antimicrobial activity of the resulting composites was determined using the agar diffusion method. Results. Through the optimization of the mineral media and the change of cultivation conditions, it was possible to obtain 0.26–1.45 g/l of polyhydroxyalkanoates (5.1–34.0% PHA from biomass). The R. ruber UCM Ac-288 strain synthesized the maximum amount of biopolymer (34.0% PHA). This study established the ability of Gordonia bacteria to synthesize PHA for the first time. PHA compositions of optimal content were obtained, with hydrophobicity comparable to that of polyethylene packaging films. Antimicrobial pro­perties of biopolymers composites with biocides have been substantiated. Conclusions. The bacterial synthesis of PHA was increased by modifying nutrient media. Composites based on PHA with biocides were developed. It was determined that these composites exhibit antimicrobial properties and high hydrophobicity. Consequently, they hold promise for use as biofilms for packaging and preser­ving food products.

Keywords

• polyhydroxyalkanoates
• rhodococcus
• azotobacter
• gordonia
• antimicrobial composites
• packaging biofilms