Changes in Fungal and Bacterial Diversity During Vermicomposting of Industrial Sludge and Poultry Manure Mixture: Detecting the Mechanism of Plant Growth Promotion by Vermicompost

Agriculture is facing a challenge to develop strategies for sustainability that can conserve non-renewable natural resources, such as soil and enhance the use of renewable resources such as organic wastes. It has been estimated that more than 18 metric tons of organic sludge was generated every day in Korea in 2003 (Anonymous, 2004)while it was 105 metric tonnes per year in India (Chitdeshwari and Savithri, 2004). Among different options for recycling this sludge, application to agricultural land is probably the most reliable and costeffective technique to supply organic matter to field crops (Coker et al., 1987). But direct application of this sludge to agricultural land might cause heavy metal contamination (McGrath, 1994). Under this perspective, industrial sludge (IS) was recycled after bioremediation involving earthworms. Unlike several chemical methods, removal of heavy metals by biological means is more specific, eco-friendly and economical. Begum and Krishna (2010) revealed that heavy metal content in organic wastes reduced after passage through earthworm guts. Therefore, industrial sludge could be recycled through vermicomposting to produce nutrient rich plant amendment. Vermicomposting is the stabilization of organic substrates by microorganisms in presence of earthworms. Though earthworms consume fungi with organic substrates to fulfil their nitrogen requirement, the viable fungal count in earthworm casts was generally higher than that of initial waste substrates during vermicomposting (Edwards and Bohlem, 1996). Ergosterol, marker molecule of fungal cell membrane, is frequently used in microbiology to quantify fungal biomass in infected media. Madan et al. (2002) estimated fungal biomass in soil by FAME assay. Hill et al. (2000) also quantified fungal specific FAME (18:19ωc) to estimate fungal biomass in compost. Yasir et al. (2009) revealed that bacterial biomass also played important role during organic matter decomposition. Muramic acid