Biodegradation of polypropylene microplastics by Bacillus pasteurii isolated from a gold mine tailing

Microplastics (MPs) are present throughout the environment, and due to their nature, they are extremely difficult to decompose. Reportedly, microorganisms play an important role in degrading and decomposing MPs. Bacillus pasteurii can degrade various complex organic matter, including MPs, which are a class of polymeric organic compounds. This study investigated the degradation effect of B. pasteurii on polypropylene MPs (PP-MPs) in soil. B. pasteurii was extracted from gold mine tailings. Herein, three experimental groups were established—a blank control treatment group, a group with bacteria without Ca²⁺ added (T2 group), and a group with bacteria supplemented with Ca²⁺ (T3 group)—for a 30-day indoor simulation of MP degradation in MP-treated soil. The results showed that the total mass change rate of the PP-MPs in the T2 group was 20.95 %, and grooves and holes appeared on the PP-MP surfaces. The total mass change rate of the PP-MPs in the T3 group was 23.22 %, and abundant fissures and pits appeared on the PP-MP surfaces. Additionally, new dominant phyla, such as Bacteroidetes and Firmicutes, appeared after bacterial addition. The relative abundance of several common soil genera, such as Bacillus, Brevundimonas, Flavobacterium, and Arthrobacter, and genera capable of breaking down complex compounds increased after B. pasteurii addition. The soil microbial community diversity improved, with the distribution of each species being relatively uniform. These findings indicated that the B. pasteurii strain can be used to degrade PP-MPs. Additionally, the addition of Ca²⁺ generated microbially induced calcium carbonate precipitation, which further improved the degradation of MPs. This study provides theoretical support for studying the degradation mechanism of PP-MPs.