Gut Bacteria Present in Greater Wax Moth (Galleria mellonella L.) Larvae Aid in Degradation of Wax and other Complex Polymers

Greater wax moth (GWM), Galleria mellonella (Lepidoptera: Pyralidae), is a destructive pest of honeybee hives. They lay eggs in the bee hives; and the hatched larvae feed on beeswax. The unique ability of GWM to digest the beeswax that contains ethene (CH2=CH2) bond has attracted attention because the same bond is also present in plastic polymers. Polymer-digesting ability, being a very uncommon among animals, we suspected a assistive role of gut bacteria of the insect in the process. The present study aimed to isolate and characterize potential polymer-degrading bacteria from GWM gut, following a culture-dependent approach, and to characterize them morphologically, biochemically, and with 16S rDNA sequences. We also intended to study polymer-degrading abilities of those bacteria, and check the presence of esterase, one of the most potent enzymes involved in plastic polymer degradation, using tributyrin agar test. We found nine bacterial isolates from GMW gut. Out of them, six showed positive results for plastic degradation to varying extents (19.3-31.2%), after 30 days of co-culture with plastic sheets. The esterase enzyme was found to be present in all of them in a qualitative test. Through 16S rDNA sequencing, four isolates were identified as gram-negative Serratia marcescens strains, one as gram-negative Ralstonia pickettii and one as gram-positive Bacillus cereus, some of which are known potential polymer degraders. Therefore, our hypothesis of involvement of gut bacteria in the digestion of polymers by Greater wax moth larvae was perhaps correct. There is possibility of exploiting the bacterial isolates for plastic-pollution remediation; after deeper and further experimentation.