Bacillus subtilis and Halomonas meridiana isolated from saline sandy soils mediate the biodegradation of polyvinyl chloride (PVC) microplastics

Microplastics are notorious class of environmental pollutants that are added to the environment by the slow degradation of plastic infrastructure commonly used everywhere. Microplastics are small particles that tend to flow through the xylem vessels of plant roots and bioaccumulate in the plant tissues. Saline sandy soil in the United Arab Emirates (UAE) is colonized by beneficial bacterial strains that exhibit plastic degradation properties. This area is of great interest for new insights; however, very little is known about microplastic-degrading microorganisms, particularly in the Middle Eastern region of the world. To fill this gap, bacterial strains isolated from hypersaline soil offer a promising and sustainable approach to mitigate microplastic pollution in the form of granular biofertilizer and liquid cell suspension in soil and soilless crop production systems. The following study entails the relative potential of Bacillus subtilis and Halomonas meridiana, identified by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF-MS), to mineralize plastics by forming biofilms. The study indicated the plastic biodegradation efficiency of the bacterial strains ranged from as low as 6.42 ± 5.73 % and as high as 16.95 ± 3.37 % in liquid and solid culture media, with an average of 10 % loss of polymer weight. The bacterial strains exhibited a strong ability of biofilms (optical density ≥0.3–0.5) and enzymatic activity (enzymatic units ≥0.006–0.01), confirmed by optical density spectrophotometric absorbances. Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry (SEM-EDS) and Fourier Transform Infrared Spectroscopy (FTIR-S) revealed the formation of minerals, oxidation, increased O/C ratios, and significant variation in the surface anatomy of plastic particles co-cultured with bacteria. The complete absence of the C-Cl peak as a result of FTIR and the highest O/C of (0.600) as a result of SEM-EDS suggested the high degradation efficiency of B. subtilis as compared to H. meridiana. These outcomes confirm the incidence of plastic degradation efficiency and biofilm formation ability of B. subtilis and H. meridiana in both the solid and liquid matrix, signifying their dual application as granular biofertilizer as well as cell suspension to minimize the traces of plastic particles in the agricultural production systems purifying the tropic level of the food chain.