Indigenous Bacillus thuringiensis and Bacillus cereus from Pasuruan mangrove sediment initiate early-stage degradation of UV-pretreated PET and PS microplastics

Abstract. Sari SHJ, Yahya, Salmabila PS, Trianto D, Arianto RD, Fauziah AH, Yona D. 2026. Indigenous Bacillus thuringiensis and Bacillus cereus from Pasuruan mangrove sediment initiate early-stage degradation of UV-pretreated PET and PS microplastics. Biodiversitas 27 (10): d271007. https://doi.org/10.13057/biodiv/d271007. Mangrove sediments contain diverse microorganisms with specialized metabolic traits, yet functional biodiversity of mangrove-associated bacterial resources remains underexplored. This study conducted an initial isolate-level screening of indigenous bacteria closely related to Bacillus thuringiensis and Bacillus cereus from a composite sample in Pasuruan tropical mangrove sediment, East Java, Indonesia, identified using 16S rRNA gene Sanger sequencing and evaluated their potential to degrade Polyethylene Terephthalate (PET) and Polystyrene (PS) microplastics. Biodegradation experiments were conducted in triplicate using 30 ppt mineral salt medium containing 30-day UV-pretreated PET and PS microplastics smaller than 250 µm over a 40-day incubation period. Both strains showed active growth during the experiments, as indicated by OD600 values exceeding those of the control treatment. Results showed that B. thuringiensis achieved higher apparent mass loss on PS (25.78%) than PET (15.92%), while B. cereus displayed similar apparent mass loss for both plastics (26%). Abiotic controls recorded negligible apparent mass loss (PET: 2.02%, PS: 1.73%), confirming that the measured mass reduction was primarily attributable to bacterial activity. Scanning electron microscopy revealed surface erosion and morphological changes on both polymers. However, Fourier Transform Infrared Spectroscopy detected only minor chemical structure changes. Together, these results point to early-stage biodegradation of UV-pretreated PET and PS, marked by biodeterioration and biofragmentation with limited chemical transformation, providing preliminary evidence of functional microplastic-degrading isolates in Pasuruan mangrove sediment.