Polystyrene degradation by bacteria isolated from the larvae of Rhynchophorusphoenicis

Abstract

The larvae of insects of the order Coleoptera have been reported to biodegrade plastics aided by their chewing mouthparts and the  activities of their gut biota. However, there is no report of this ability by the African palm weevil (Rhynchophorus phoenicis). This study  aims to the ability of R. phoenicis larvae to biodegrade polystyrene (PS). A total of 100 R. phoenicis larvae were fed for 21 days with PS  foam, and afterwards, the gut contents of survivors were investigated for possible PS-degrading bacteria. Bacterial isolates were  screened for PS biodegradation in an Erlenmeyer flask with PS film as the sole carbon source, in a mineral salt medium (MSM) at a temperature of 30^oC and a pH of 7, for a period of 28 days. The isolates were used for biodegradation assay under the same conditions,  for 60 days. The weight of PS films was determined before and after the biodegradation assay. Chemical changes in the films were confirmed by Fourier Transform Infrared (FTIR) spectroscopy. Two bacterial isolates were recovered from the gut of the only surviving R.  phoenicis larvae fed with 100% PS. The isolates were identified based on their 16S rRNA sequences as Lysinibacillus macriodes and  Pantoea dispersa with accession numbers OQ652017 and OQ652023 respectively. The isolates caused an 8.8% reduction in the weight of  PS film and FTIR spectroscopy results confirmed the formation of groups suggestive of degradation products with the carbonyl group  showing up as absorption peaks in the range of 1640-1760 cm^-1 and the hydroxylic group at 3000-3700 cm^-1 . The isolates were able to  produce polyhydroxyalkanoate (PHA) equivalent to 1.4g/L, under PS degradation conditions. Therefore, coupling the biodegradation of  PS with PHAproduction could be useful for the valorization of PS waste.