Plastic-degrading bacteria isolated from contaminated mangrove sediment in Wonorejo, Surabaya

Plastics have become inevitable needs in modern society due to their attractive properties, including thermostability, lightweight, flexibility, superior insulation, and low cost, which have led to massive production. Their persistence and challenges in disposal have detrimental effects on the environment leading to the development of a promising degradation process which is efficient, time-saving, and cost-effective. This study focused on discovering the potential plastic-degrading bacteria isolated from plastic-contaminated mangrove sediment in the Wonorejo area. We buried a commercially available plastic bag in the polluted mangrove sediment for 16 weeks. Our results showed that indigenous bacteria formed a biofilm on the plastic surface leading to a plastic dry weight loss of up to 12%. FTIR analysis revealed obvious transmittance attenuations in the buried plastic polymer, suggesting that their chemical properties may have been interrupted due to bacterial activity. Further, bacteria isolation and biochemical screening revealed that they were primarily dominated by Bacillus. According to 16S rRNA sequencing, they were identified as Brevibacilllus (BIO-B), Stenotrophomonas (BIO-G), and Lysinibacillus (SOI-C). The three genera mentioned earlier exhibited a detectable level of plastic-degrading activity and possessed lipolytic, ligninolytic, and alkanedegrading activities. Stenotrophomonas (BIO-G) showed a degradation activity on low-density polyethylene (LDPE) represented by a plastic dry weight loss of up to 8.9% within 4 weeks. As expected, plastic treated with BIO-G showed transmittance attenuation in FTIR analysis, albeit with a lower percentage than that treated with indigenous bacteria. Moreover, SEM analysis reveals changes in the morphological surface of plastic. Together, FTIR and SEM analysis indicated that bacteria disrupt both the chemical structure and morphological appearance of plastic polymer upon degradation process. These results denote that BIO-G indeed composes the aforementioned indigenous bacteria from polluted mangrove sediment. Thus, our study suggests the indigenous bacteria isolated from contaminated areas produced plastic-degrading enzymes and secreted to the environment to break down plastic compounds.