Role of earthworms' mucus in vermicomposting system: Biodegradation tests based on humification and microbial activity

During vermicomposting, the organic wastes can be recycled into high-value products as mediated by earthworms through gut digestion, burrowing, casting and mucus excretion. However, to date, few studies have been done on the role of mucus in vermicomposting system compared to the effects of the other activities. Hence, this study investigated the potential role of earthworms' mucus in the decomposition and humification of organic wastes. For this, the mucus of Eisenia fetida was extracted and inoculated into three vermicomposting substrates using cow dung (CD), fruit and vegetable wastes (FVW), and sewage sludge (SS). The results obtained after a 20 day experiment showed that the mucus could accelerate the mineralization and humification rates of organic components. The dissolved carbon showed 9.8%–37.5% increase in treatments containing mucus, higher than those in substrates without mucus. Moreover, the mucus significantly stimulated the microbial activity and bacterial abundance, showing the greatest increases in FVW treatments. In addition, the mucus positively stimulated growth of Proteobacteria, but negatively affected the Firmicutes during decomposition. This result suggests that the earthworms' mucus significantly accelerated the decomposition and humification of vermicomposting materials, and could even promote microbial activity, growth, and increase community diversity in vermicomposting systems.