1.2.4 Microbes in compostingComposts contain a large and very diverse microbial community (mainly bacteria and fungi), which plays a key role in the decomposition of organic matter during the various temperature phases of composting. At the beginning of the composting process, mesophilic bacteria, typically from the genera Lactobacillus and Bacillus (Partanen et al., 2010), predominate. Their populations significantly increase during the early phase of composting, as they are capable of degrading the soluble and readily degradable compounds such as sugars, and heat is produced by their metabolic activities. As the temperature rises to about 40 °C, thermophilic bacteria such as Actinobacteria, Bacillus, and Thermus take over the degradation and become the dominant groups in the microbial community. Actinobacteria and Bacillus have been described as indicators of the well-functioning composting (Partanen et al., 2010). Actinobacteria, previously documented as Actinomycetes, have been reported as a critical group in the composting process, since they can utilize a wide range of carbon sources such as cellulose, lignin and proteins (Epstein, 1996). Some species of Actinobacteria are thermotolerant and can remain active at temperatures of up to 60 °C. In addition, they have been found to be ineffective competitors when nutrient levels are high, thus becoming more competitive in a low nutrient environment (Nakasaki et al., 1985). During the composting process, Actinobacteria typically predominate in the thermophilic and 2n mesophilic (cooling) phases, and
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