Marine-Derived Actinomycetes: Biodegradation of Plastics and Formation of PHA Bioplastics—A Circular Bioeconomy Approach

Abstract

Plastics are present in the majority of daily-use products worldwide. Due to society’s production and consumption patterns, plastics are accumulating in the environment, causing global pollution issues and intergenerational impacts. Our work aims to contribute to the development of solutions and sustainable methods to mitigate this pressing problem, focusing on the ability of marine-derived actinomycetes to accelerate plastics biodegradation and produce polyhydroxyalkanoates (PHAs), which are biodegradable bioplastics. The thin plastic films’ biodegradation was monitored by weight loss, changes in the surface chemical structure (Infra-Red spectroscopy FTIR-ATR), and by mechanical properties (tensile strength tests). Thirty-six marine-derived actinomycete strains were screened for their plastic biodegradability potential. Among these, Streptomyces gougerotti, Micromonospora matsumotoense, and Nocardiopsis prasina revealed ability to degrade plastic films—low-density polyethylene (LDPE), polystyrene (PS) and polylactic acid (PLA) in varying conditions, namely upon the addition of yeast extract to the culture media and the use of UV pre-treated thin plastic films. Enhanced biodegradation by these bacteria was observed in both cases. S. gougerotti degraded 0.56% of LDPE films treated with UV radiation and 0.67% of PS films when inoculated with yeast extract. Additionally, N. prasina degraded 1.27% of PLA films when these were treated with UV radiation, and yeast extract was added to the culture medium. The main and most frequent differences observed in FTIR-ATR spectra during biodegradation occurred at 1740 cm−1, indicating the formation of carbonyl groups and an increase in the intensity of the bands, which indicates oxidation. Young Modulus decreased by 30% on average. In addition, S. gougerotti and M. matsumotoense, besides biodegrading conventional plastics (LDPE and PS), were also able to use these as a carbon source to produce degradable PHA bioplastics in a circular economy concept.

Degradation of Biodegradable Microplastics under Artificially Controlled Aging Conditions with UV Radiation

“…It was also found that the crystallinity of PBAT exposed to aqueous environment did not change after UV treatment [44]. In addition, the contribution of microorganisms to the degradation of BPs cannot be ignored, as they secrete various enzymes that can effi ciently promote the degradation of BPs, and studies have shown that with the radiation of UV could achieved a better degradation eff ect [45,46]. In fact, whether exposure to UV radiation in the natural environment is suffi cient to enhance biodegradation remains to be demonstrated.…”

Biodegradation of Typical Plastics: From Microbial Diversity to Metabolic Mechanisms

“…Gordonia sihwensis , Gordonia mangrovi , and Gordonia bronchialis isolated from mangroves showed PS degradability with 4.69–7.73% degradation rates in one month [ 73 ]. Srreptomyces gougerotti , Micromonospora matsumotoense , and Nocardiopsis prasina isolated from the ocean could degrade LDPE, PS, and polylactic acid (PLA) to varying degrees [ 77 ].…”

Sustainable bioconversion of synthetic plastic wastes to polyhydroxyalkanoate (PHA) bioplastics: recent advances and challenges

“…PS is the fifth mostly used synthetic polymer 93,94 in packaging materials, food containers and construction materials. 95,96,97 PS is an aromatic thermoplastic with a C-C backbone, 81 makes its biodegradation very difficult.…”