Fungal and bacterial successions in the process of co-composting of organic wastes as revealed by 454 pyrosequencing.

Anatoly Saveliev,Eugenia Boulygina,Liliya Biktasheva,Francisco Martinez-Abarca,Svetlana Selivanovskaya,Tatiana Grigoryeva,Polina Galitskaya

doi:10.1371/journal.pone.0186051

Abstract

Composting is viewed as one of the primary methods to treat organic wastes. Co-composting may improve the efficiency of this treatment by establishing the most suitable conditions for decomposers than those present in the individual wastes. Given that bacteria and fungi are the driving agents of composting, information about the composition of their communities and dynamics during composting may improve reproducibility, performance and quality of the final compost as well as help to evaluate the potential human health risk and the choice of the most appropriate application procedure. In this study, the co-composting of mixtures containing two similar components (organic fraction of municipal solid waste and sawdust polluted by oil) and one discriminate component (sewage sludges of different origin) were investigated. Bacterial and fungal community successions in the two mixtures were analyzed during the composting process by determining the change in their structural dynamics using qPCR and 454 pyrosequencing methods in a lab experiment for a period of 270 days. During the initial composting stage, the number of 16S bacterial copies was (3.0±0.2) x 106 and (0.4±0.0) x 107 g-1, and the Rhodospiralles and Lactobacialles orders dominated. Fungal communities had (2.9±0.0) x105 and (6.1±0.2) x105 ITS copies g-1, and the Saccharomycetales order dominated. At the end of the thermophilic stage on the 30th day of composting, bacterial and fungal communities underwent significant changes: dominants changed and their relative abundance decreased. Typical compost residents included Flavobacteriales, Chitinophagaceae and Bacterioidetes for bacteria and Microascaceae, Dothideomycetes, Eurotiomycetes, Sordariomycetes, and Agaricomycetes for fungi. During the later composting stages, the dominating taxa of both bacterial and fungal communities remained, while their relative abundance decreased. In accordance with the change in the dominating OTUs, it was concluded that the dynamics of the bacterial and fungal communities were not similar. Analysis by non-metric multidimensional scaling (NMDS) revealed that the bacterial communities of the two composts became progressively more similar; a similar trend was followed by the fungal community.

Highlights

Accelerated by exponential population growth and increased consumption per capita, organic wastes have become a serious environmental problem in the past decades [1]
The temperature peak observed on the 20th-24th days of composting in both mixtures, the dissolved organic carbon (DOC) level fell significantly during the first four weeks and remained stable, and the Germination index (GI) reflecting the maturity of the composts exceeded 100% on the 270th day
Summarizing the results obtained for each compost we can suggest that the mesophilic stage in both composts lasted for 16 days, and the thermophilic stage lasted for approximately 12 days

Summary

Introduction

Accelerated by exponential population growth and increased consumption per capita, organic wastes have become a serious environmental problem in the past decades [1]. They can be treated with appropriate energy and resources. Interest in compost microbiota has increased significantly due to the fact that bacteria and fungi are the two main driving forces of composting, and efficient composting is dependent on the presence of a high microbial diversity [3,4,5,6,7]. Understanding the changes in microbial communities during composting may improve reproducibility, performance, quality of the final compost as well as the evaluation of potential human health risks and choice of the optimal application procedure [11,12,13]

Methods

Results

Conclusion