In vitro degradation of low-density polyethylene by new bacteria from larvae of the greater wax moth, Galleria mellonella

Abstract

Three bacterial species isolated from whole body extracts of the greater wax moth larvae, Galleria mellonella, were evaluated for their ability to utilize low-density polyethylene (LDPE) as a sole carbon source in vitro. These bacteria were identified as Lysinibacillus fusiformis, Bacillus aryabhattai, and Microbacterium oxydans. Their ability to biodegrade LDPE was assessed by growth curves, cell biomass production, polyethylene (PE) weight loss, and the presence of LDPE hydrolysis products in the growth media. Consortia of these bacteria with three other bacteria previously shown to degrade LDPE (Cupriavidus necator H16, Pseudomonas putida LS46, and Pseudomonas putida IRN22) were also tested. Growth curves of the bacteria utilizing LDPE as a sole carbon source revealed a peak in cell density after 24 h. Cell densities declined by 48 h but slowly increased again to different extents, depending on the bacteria. Incubation of LDPE with bacteria isolated from greater wax moth larvae had significant effects on bacterial cell mass production and weight loss of LDPE in PE-containing media. The bacterial consortia were better able to degrade LDPE than were the individual species alone. Gas chromatographic analyses revealed the presence of linear alkanes and other unknown putative LDPE hydrolysis products in some of bacterial culture media.

Wax worm saliva and the enzymes therein are the key to polyethylene degradation by Galleria mellonella

“…The capacity of Galleria mellonella as well as other Coleoptera and Lepidoptera to degrade sturdy polyolefin-derived polymers as PE or PS has been extensively documented in the past few years, with no pretreatment required for the plastic polymer to be degraded [26][27][28][29][31][32][33][34][35][36][37][38][42][43][44][45][46][47] . If this capacity resides in the microorganisms of the worm gut, in the itself, or in a complementation of the two, is still an object of debate.…”

“…The gut microbiome has traditionally been considered the culprit of plastic degradation by insects. However, despite the numerous reports appeared lately about microbe species being potentially responsible for insect-driven plastic biodegradation, no consensus on specific species or genera of bacteria/fungi colonizing the Lepidoptera and Coleoptera gut and involved in plastic degradation has been reached [26][27][28]30,31,[34][35][36][37][38]43 . Indeed, the exclusive involvement of microorganisms in this process has been recently questioned 32,48 .…”

Lessons From Insect Fungiculture: From Microbial Ecology to Plastics Degradation

“…Microbial communities associated with insect fungiculture are interesting to prospect for microbes and enzymes targeting plastic degradation. Innovative biotechnological approaches were already inspired by insect gut microbiota, branching possibilities for bioremediation research ( Bredon et al, 2018 ; Jang and Kikuchi, 2020 ; Kim et al, 2020 ; Montazer et al, 2021 ; Yang et al, 2021 ). Insect fungiculture is associated with microbial communities that often biodegrade plant polymers.…”

Why have we not yet solved the challenge of plastic degradation by biological means?

“…Plastic degradation + CO 2 coleopterans Tenebrio molitor and Zophobas atrum have been described as being capable of breaking down PE and/or PS [13][14][15][16][17]. Given the current metabolic paradigm of plastic degradation by biological means, these discoveries were followed by a rush to analyze the gut microbiota of these insects [30][31][32][33][34][35][36], a continuing trend (Fig 1C). To date, not only has no specific plastic-degrading microbe been positively identified, but the dependence of plastic degradation on gut bacteria has been called into question [37,38].…”