Keiko Watanabe, Norio Nagao, Tatsuki Toda, and Norio Kurosawa

Abstract Composting is an efficient and cost-effective process for organic waste treatment. In order to expand our knowledge regarding microorganisms in the com­posting reactor, bacterial community structures in a variety of composting processes were examined by 16S rRNA gene (rDNA) clone analysis including denaturing gradient gel electrophoresis (DGGE), as a case study. As previously reported, the dominant bacteria consist of members of the order Bacillales in a typical compost­ing condition with woodchips as the bulking agent. However, these aerobic bacteria decreased to 14%, and anaerobes or facultative anaerobes arose when the decom­position rate of organic compounds dropped following aggregation of the contents. In the composting reactor operated with plastic bottle flakes as bulking agent, the order Lactobacillales co-dominated with the Bacillales, regardless of reactor size, accounting for about 70% of the detected organisms during first week of the opera­tion, gradually decreasing to about 30% with maturation of the composting process. Most species detected by clone analysis have not been cultivated, and may be VBNC (viable but non-culturable) species, implying symbiotic interactions among the microorganisms. In addition, the 16S rDNA-clone and DGGE methods are also introduced in this chapter.

Keywords Aggregate ■ Bacterial community ■ Bulking agent ■ Clone analysis ■ Compost ■ Denaturing gradient gel electrophoresis (DGGE) ■ Large-scale fed-batch composting reactor ■ Plastic bottle ■ Polyethylene terephthalate ■ 16S rRNA gene (16S rDNA)

K. Watanabe (B)

Faculty of Engineering, Department of Environmental Engineering for Symbiosis, Soka University, 1-236, Hachioji, Tokyo, Japan e-mail: kewatana@soka. ac. jp

O. V. Singh, S. P. Harvey (eds.), Sustainable Biotechnology,

DOI 10.1007/978-90-481-3295-9_8, © Springer Science+Business Media B. V. 2010

1 Introduction

Composting is one of the efficient and cost-effective biological processes to treat organic waste. However, some trouble may occur in a composting reactor, for exam­ple, aggregation of contents, decreasing pH and decreasing rate of decomposition. In composting processes, thermophilic and mesophilic microorganisms have important respective functions in terms of nutrient recycling and decomposition of complex organic substrates [1]. Therefore, an understanding of the microbial community and its succession is important to effectively manage the composting process. Thus, in this chapter, bacterial communities in the various composting reactors are revealed by using molecular biological methods, as a case study. These methods are simi­larly applicable to environmental samples, anaerobic digestion treatment reactors, and industrial reactors.