Plastic biodegradation by marine-derived actinobacteria

Abstract

Plastic is an integral part of our life, being present in most of the products that we use daily. Due to the production and consumption patterns of society, plastics are accumulating in the environment, which causes pollution issues, and intergenerational impacts on the life and health of organisms. We hypothesize that different actinobacteria strains are capable of degrading different types of (micro)plastics by using them as a carbon source, and then transformed them into bioplastics. In this way, this study aimed to find and develop solutions and sustainable methods to mitigate this environmental problem, focusing on the study of the ability of marine actinobacteria to accelerate plastics biodegradation. In this work, the screening of thirty-six marine-derived actinobacteria strains was performed to evaluate their polyvinylidene fluoride, polystyrene, and polylactic acid biodegradability potential. The selected actinobacteria (Streptomyces gougerotti, Micromonospora matsumotoense, M. terminaliae, and Nocardiopsis prasina) were used in the plastic biodegradation assays using plastic films and testing different conditions. Half of the plastic films used in the assays were pre-treated with UV irradiation and yeast extract was added to culture media to perceive its influence in biodegradation. In both cases, enhanced degradation by the microorganisms was observed. Biodegradation of films was monitored by weight loss, which was detected in all the inoculated films, except for LDPE UV films inoculated with M. terminaliae. The maximum weight loss percentage was 1.27% for PLA inoculated with N. prasina. Nocardiopsis was identified as a new genus with the ability to degrade PLA. Biodegradation was also accessed based on changes in surface chemical structure (by infra-red spectroscopy) and mechanical properties (tensile strength). The absorptions bands of carbonyl groups are the most related to biodegradation. The maximum decrease in Young modulus was 59% for polystyrene films inoculated with S. gougerotti. We conclude that S. gougerotti, M. matsumotoense, and N. prasina had the potential to use conventional plastics as a carbon source. Furthermore, S. gougerotti and M. matsumotoense were able to biodegrade conventional plastics and possibly transform them into bioplastics, through the pro-duction of PHA inclusions.