Biodegradation of polyethylene (PE), polypropylene (PP), and polystyrene (PS) microplastics by floc-forming bacteria, Bacillus cereus strain SHBF2 isolated from a commercial aquafarm

Abstract

The ubiquitous proximity of the commonly used microplastic (MP) particles particularly polyethylene (PE), polypropylene (PP), and polystyrene (PS) poses a serious threat to the environment, and human health globally. Biological treatment as an environment-friendly approach to counter MPs pollution has recent interest when the bio-agent has beneficial functions in their ecosystem. This study aimed to utilize beneficial floc-forming bacteria B. cereus SHBF2 isolated from an aquaculture farm in reducing the MPs particles (PE, PP, and PS) from their environment. The bacteria were inoculated for 60 days in a media containing MPs particles as a sole carbon source. On different days of incubation (DOI), the bacterial growth analysis was monitored and the MPs particles were harvested to examine their weight loss, surface changes, and alterations in chemical properties. After 60 DOI, the highest weight loss was recorded for PE, 6.87 ± 0.92%, which was further evaluated to daily reduction rate (k), 0.00118 gday^− 1, and half-life (t_1/2), 605.08 ± 138.52 days. The OD value (1.74 ± 0.008 Abs.) indicated the higher efficiency of bacteria for PP utilization, and so for the colony formation per define volume (1.04 × 10¹¹ CFU/mL). Biofilm formation, erosions, cracks, and fragments were evident during the observation of the tested MPs using the scanning electron microscope (SEM). The formation of carbonyl and alcohol group due to the oxidation and hydrolysis by SHBF2 strain were confirmed using the Fourier transform infrared spectroscopic (FTIR) analysis. Additionally, the alterations of pH and CO₂ evolution from each of the MPs type ensures the bacterial activity and mineralization of the MPs particles. The findings of this study have confirmed and indicated a higher degree of biodegradation for all of the selected MPs particles. B. cereus SHBF2, the floc-forming bacteria used in aquaculture, has demonstrated a great potential for use as an efficient MPs degrading bacterium in the biofloc farming system in the near future to guarantee a sustainable green aquaculture production.