An assessment of bacterial populations in a static windrow compost pile

Many companies, restaurants, colleges, as well as individual homeowners, have initiated green marketing campaigns, and the composting of food and yard wastes has become commonplace. Thus, it is essential to obtain a more complete understanding of the microbial populations present in such composting processes. The focus of this study was to identify bacterial populations in a static windrow compost pile initiated on a college campus containing food trim and tree debris. Given that the compost pile was initiated during the winter it was uniquely characterized by a pre-mesophilic stage in addition to the characteristic mesophilic, thermophilic, and cooling/maturation stages. Bacteria were cultured from each stage and were identified by sequencing the 16S rRNA gene. Dominating the numbers throughout the study were bacteria within the Bacillus and Bacillus-like genera. Actinobacteria were found primarily within the pre-mesophilic stage. The mesophilic and beginning thermophilic stages displayed the most diversity, characterized by several different genera within the Proteobacteria phylum. In contrast, during the late thermophilic stage, only bacteria within the Bacillus and Brevibacillus genera were cultured. Overall, 49 different species within 27 different genera, 13 families, and 4 phyla, were identified and several genera that have not been commonly associated with household compost. Thus, this study supports a role for the continuation of culture-dependent studies to more completely define the bacterial flora involved in various composting processes.