Comparative Investigation of Vermicompost Microbial Communities

Abstract

In the present study gas chromatography-mass spectrometry (GC-MS) methods were applied for investigation of worm compost (via Eisenia fetida culture). Sewage sludge (SS) and cattle manure (CM) were used as raw matter for compost preparation. Total percentage of carbon increased from 13% (for SS vermicompost) up to 50% (CM vermicompost), while the ratio of C:N from 22 – 42 up to 22 for SS and CM, respectively, has been shown. The contents of total nitrogen (N = 1−2%), potassium (K20 = 1.1−1.4%) and phosphorus (P205 = 0.6−1.5%) have been measured. The concentrations of heavy metals such as Cd, Cu, Cr, Ni, Pb, Zn in organic matter after digestion by earthworms decreased by two to six times. The greatest reduction was observed for Cr and Zn concentrations and the smallest for Ni. Lipid biomarker analysis revealed altogether 21 genera of microorganisms in vermicomposts community representing a number of trophical groups. The abundance of microorganisms from genera Acetobacter, Sphingobacterium, Aeromonas, Vibrio and Streptomyces increased remarkably after SS vermicomposting procedure. Quantitative comparison of microbial biodiversity showed, that three genera dominated in CM vermicompost: Bdellovibrio (and/or Spirillum) usually inhabitanting in wastewater (17%); Bacteroides (15%) and Clostridium (17%), which are common for rumen. The four following genera dominated in cenoses from SS composts: Acetobacter (20%), Pseudomonas (11%), Wolinella (12%) and Bacteroides (10%), making totally 61%. Supposedly, prevalence of genera Acetobacter and Wolinella may improve nitrogen metabolism in compost matter. The SS community had two dominating genera: Pseudomonas (27%) and Bacteroides (37%). Acquired data demonstrates prevalence of microorganisms with high hydrolyzing activity. They are spore forming (Bacillus), mycelial (Streptomyces, Nocardia, representatives of the Maduromycetes group) and cellulolytic (Cytophaga) microorganisms. Their products serve as substrates for fermenting organisms (Bacteroides, Clostridium, Vibrio, Wolinella). Later, members of Acetobacter, Pseudomonas, Sphingobacterium, Sphingomonas use simple organic material formed after hydrolysis and fermentation in aerobic conditions.