Comparative seasonal analysis of Eri silkworm (Samia ricini Donovan) gut composition: implications for lignocellulose degradation

Abstract

Conversion of biomass such as lignocelluloses to alternative energy source can contribute to sustainable development. Recently, biomass degrading enzymes are reported to be common resources in insect-microbe interacting systems. North-East India harbours ample sericigenous insect resources which are exploited for their silk products. Samia ricini Donovan is an economically important poly-phytophagous silkmoth capable of digesting foliage from different plant species, suggesting versatility of robust gut system. Here, gut bacterial profile was determined by 16S rRNA gene characterization across the holometabolous life cycle during summer and winter seasons revealing 3 phyla, 13 families and 22 genera. Comparative analysis among the seasonal gut isolates revealed a high diversity in summer, predominated by genus Bacillus due to its high occurrence in all developmental stages. Shannon’s diversity index demonstrated second and fourth instars of summer as well as fifth instar of winter to be relatively better developmental stages for gut bacteria assemblance. Bacterial community shifts in concert to host developmental changes were found to be apparent between early instars and late instars in summer which differs from those of winter. Forty-three and twenty-nine gut isolates were found to be a potential cellulolytic and xylanolytic enzyme producers. Our results illustrates gut microbiota of S .ricini over the seasons and support holometabolous life cycle effect as the more likely factor shaping gut bacterial microbiota. These findings may provide leads for development of new cleaner and environment friendly lignocelluloses degrading enzymes.

Midgut serine proteinases participate in dietary adaptations of the castor (Eri) silkworm Samia ricini Anderson transferred from Ricinus communis to an ancestral host, Ailanthus excelsa Roxb

“…Efforts to reutilize ancestral host plants, such as A. excelsa , may benefit from studies on microbial communities associated with S. ricini larvae feeding on different diets. Recent information suggests that there are dynamic communities of aerobic and anaerobic gut endosymbionts in S. ricini larvae feeding on R. communis with the potential to utilize complex substrates such as lignocellulose ( 92 , 93 ). Detailed characterization of the microbial constituents, metagenomes, and functions of the larval “holobiont” ( 94 , 95 ) in S. ricini feeding on various hosts, such as R. communis and A. excelsa , may pay rich dividends in improving the commercial productivity of this economically important domesticated polyphagous silkworm to the benefit of its indigenous rearers.…”