Community-level genetic profiles of actinomycetales in long-term biowaste-amended soils

Actinomycetales is an order of actinobacteria that have an important role in the decomposition of organic matter. Their abundance and distribution can reflect a good level of soil fertility as well as biological activity. In this research study, actinomycetal diversity in soil was investigated under various field treatments with biowastes. Initially, unvegetated agricultural soil plots of 4 m² had been annually amended with increasing rates of municipal solid waste compost (MSWC at 40, 80 and 120 t ha^-1 year^-1) and farmyard manure (FM at 40 and 120 t ha^-1 year^-1) for eight consecutive years. Control consisted of unamended soil and all treatments were distributed in four randomized complete blocks. At the end of the experimental period, total DNA was extracted from fresh topsoil samples (0-20 cm) then nested PCR-DGGE sequencing method was applied to assess the long-term effect of treatments on the diversity of actinomycetes. Analytical outcomes revealed the presence of ten actinomycetal families with Streptomycetaceae, Pseudonocardiaceae and Nocardioidaceae being the most dominant regardless to changes in experimental conditions. Besides, the long-term accumulation of both biowastes in soil affected the diversity of actinomycetal communities in different ways including contribution, stimulation or inhibition. Interestingly, soil treated with MSWC at an equivalent rate of 40 t ha^-1 year^-1 was likely to provide optimal growth conditions for major identified genera because it showed the highest actinomycetal diversity as compared to the rest of the treatments.