Paenibacillus lautus isolated from the Sphenophorus levis gut causes structural and physicochemical changes on polystyrene surface

TL;DR

A bacterium from beetle larvae gut can break down polystyrene, causing structural and chemical changes that could help in bioremediation.

Contribution

Identification of Paenibacillus lautus as a novel PS-degrading bacterium with potential for bioremediation.

Findings

Paenibacillus lautus alters polystyrene surface topography, creating pits and cracks.

Surface oxidation and reduction in molecular weight of polystyrene were confirmed.

Genes encoding potential PS-modifying enzymes were identified in the bacterium's genome.

Abstract

Polystyrene (PS) is a petroleum-based polymer with a recalcitrant structure. Along with the increasing demand, its accumulation in the environment is evident, leading to societal and ecosystemic issues. Therefore, research has focused on strategies for PS biodegradation. Certain insect larvae have been reported to use PS as a carbon source, which depends on their gut microbiota. In this context, we investigated the biodegradation ability of bacteria from the gut of the Sphenophorus levis larvae.

Larvae of S. levis were fed expanded polystyrene. Their gut contents were inoculated into a carbon-free liquid medium with PS films. The enriched bacteria were isolated and identified by 16S rRNA gene sequencing. The bacteria were cultured on a carbon-free solid medium in contact with a PS film. After, the films were analyzed by Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Fourier Transform Infrared Spectroscopy (FT-IR). Molecular weight changes were assessed by gel permeation chromatography (GPC) using PS films incubated in liquid medium. Whole-genome sequencing of total bacterial DNA was performed using the Illumina platform.

From the five strains isolated from the enrichment, a Paenibacillus lautus strain presented the most promising results. Bacteria appeared to be attached to the polymer, altering its topography and forming pits and cracks. Surface oxidation was confirmed by EDS and FT-IR, which detected oxidation-related functional groups, including hydroxyls and carbonyls. The GPC analysis revealed a reduction in the molecular weight of the treated films. Sequencing revealed a 6,950,071 bp genome with an average GC content of 51.11%. Forty contigs were obtained, with 98.9% completeness when compared with the Bacillales ortholog database. Genes encoding putative PS-modifying enzymes, such as peroxidases, ring-cleaving oxygenases, cytochrome P450, and monooxygenases, were identified.

The topographical and chemical modifications, together with the changes in molecular weight, provide evidence that the P. lautus strain alters the polystyrene structure. Therefore, this strain might be an interesting agent of polystyrene bioremediation, together with its proteins, which will be further studied in the future.

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