Prospecção e caracterização de microrganismos intestinais do coleóptero Sphenophorus levis e suas enzimas com potencial para biodegradação de poliestireno

Abstract

Polystyrene (PS) is a polymer with versatile physical and chemical properties and a low production cost, used for various purposes. Its growing demand, combined with poor waste management, leads to accumulation in the environment, triggering social and ecosystem problems. This issue is exacerbated because PS is a recalcitrant polymer due to its carbon–carbon (C–C) main chain, which makes its biodegradation in nature difficult. Studies have investigated strategies for the biodegradation of this polymer. It has been found that larvae of certain insects are capable of using PS as a carbon source, a phenomenon correlated with their gut microbiota. For this reason, the larva of Sphenophorus levis, previously observed ingesting expanded polystyrene (EPS), was used to prospect microorganisms and key genes involved in the material’s biodegradation process. The larvae were fed a diet restricted to EPS, and their intestinal microbial diversity was compared with that of larvae fed an artificial diet. It was observed that diversity decreased and the presence of its obligatory endosymbiont became more pronounced. The intestinal contents of the larvae were subjected to enrichment in a mineral medium, whose only carbon source was PS films. Five bacterial strains were isolated from the following genera: Bacillus, Lysinibacillus, Paenibacillus, Cytobacillus, and Raoultella. These were cultivated for 60 days on solid medium in contact with PS films. SEM analysis revealed cavities, cracks, and fissures in the films, and surface atom mapping indicated oxygen accumulation. FT-IR analyses indicated that only Paenibacillus sp. led to the formation of characteristic oxidation functional groups. Gel permeation chromatography indicated that the same strain was able to alter the polymer’s molar mass. To elucidate which mechanisms might be involved in this process, the entire genomes of two strains (Bacillus cereus and Paenibacillus lautus) were sequenced on the Illumina NextSeq 2000. Annotation identified proteins such as multicopper oxidases, ring-cleaving dioxygenases, cytochromes P450 (CYP), and glutathione peroxidases (GPx). CYP102 from P. lautus and the GPxs from both species were cloned and expressed in Escherichia coli. Both GPxs have thioredoxin peroxidase activity. The results demonstrate the potential of the intestinal microbiota of S. levis as a source of microorganisms and enzymes for PS biodegradation.