# Microbial and Enzymatic Biodegradation of Plastic Waste for a Circular Economy
## 2 Microbial and Enzyme-Based Degradation of Plastic
### Insect Microbiota in Plastic Degradation  
Recent studies have highlighted the potential of insect microbiota to digest plastic, largely due to the microorganisms in their guts. Research into the application of insects in the breakdown of plastics is increasing, especially research linked to insect gut bacteria or associated enzymes. Recently, [PERSON] et al. investigated how the lesser waxworm (_Achroia grisella_) larvae's stomach symbionts biodegrade low-density polyethylene plastic. The results of this study revealed that two bacterial strains, _Citrobacter freundii_ (LDPE-DB1) and _Bacillus_ sp. (LDPE-DB2), isolated from the insect's gut displayed notable degradation, with test plastic tensile strengths being reduced by 51.3% and 58.3%, respectively. During the course of the 30-day incubation period, cell densities rose, and the development of cavities on the LDPE surfaces verified the presence of bacteria [75].  
_Zophobas atratus_ larvae, commonly known as superworms, have emerged as standout performers in tackling plastic waste. A study unveiled the unique ability of _Z. atratus_ larvae to break down PS and PU foam plastics. This study revealed that feeding on plastics changes the larvae's gut microbial communities and increases specific enzyme activities. Specifically, protease activity increased, enhancing the larvae's ability to digest these synthetic polymers. Remarkable microbial shifts in gut microflora were, characterised by _Mangroviobacter_ domination in the PU-fed group, _Citrobacter_ flourished in the PE-fed group, and _Dysgonomonas_ and _Sphingobacterium_ thrived in the PS-fed group. Across all plastic-fed groups, _Enterococcus_ was found to be prominent microorganisms, suggesting its central role in the biodegradation process [76].  
Building on these findings, [PERSON] et al. conducted a comparative analysis of polystyrene biodegradation in three insect species: _Tenebrio molitor_ (yellow mealworm), _Galeria melonella_ (greater wax moth), and _Zophobas atratus_. Among these, the _Z. atratus_ (common name: superworms) larvae exhibited better degradation efficiency. Across all three species, _Enterococcus_ and _Enterobacteriaceae_ were capable of PS plastic breakdown, yet _Z. atratus_ demonstrated far greater degradation efficiency [77].  
Further advancing this narrative, [PERSON] et al. delved into the ability of _Z. atratus_ larvae to biodegradable PS and LDPE. Their study provided evidence of plastic fragmentation within the larvae's gut. This process was also linked to changes in the gut microbiota, particularly the upregulation of functional enzymes such as arylesterase and serine-hydrolase. The presence of _Citrobacter_ sp. was notably higher when the larvae consumed PS and LDPE, suggesting its potential contribution to enzymatic plastic degradation [78].  
The use of insects could be a potential large-scale biological solution for plastic waste management [79]. While the primary mechanism of plastic degradation in insects is digestion by gut enzymes from resident bacteria, the exact enzyme(s) which facilitate depolymerisation are not clear [80].