Uncovering Bacterial Diversity during Mesophilic and Thermophilic Phases of Biowaste Composting through Next-Generation Sequencing

The accumulation of biowastes is one of the main concerns of modern society. One of the most environmentally friendly solutions to convert biowaste into a product is composting. Biowastes may contain unknown substances that are persistent in the final compost, thus contributing to soil contamination and salinization. The effectiveness of the composting process depends on the microbial communities involved, which is the number of investigations' targets. The present work studied the bacterial diversity of mesophilic and thermophilic phases of composting developed in two different sites. The study was conducted through next-generation Illumina HiSeq sequencing and phylogenetic communities, revealing the dynamics and changes in specific mesophilic and thermophilic habitats of composting piles. The results showed a higher number of bacterial species in the mesophilic phase than in the thermophilic one, proved by the Shannon and Chao indices. In addition, the diversity of bacterial species expressed by the operational taxonomic units was much higher at the site of Harmanli than at the Yasno pole. Higher abundance was found of the genera Sphingobacterium, Sphingomonas, Paracoccus, Pseudomonas, and Halomonas in both studied sites. In the compost of Harmanli genera Streptomyces, Truepera, and Flavobacterium were found to be much more abundant compared to the compost of the Yasno pole. Finally, we conclude that the two plots show relatively significant differences in the diversity of bacteria during biowaste composting. Substantial differences were also observed between the mesophilic and thermophilic phases, with the first showing a significantly higher degree of species richness.