Microbial diversity and nitrogen-metabolizing gene abundance in backyard food waste composting systems

The microbial diversity of backyard compost piles is poorly understood compared to large-scale, highly regulated composting systems. The purpose of this study was the identification of the microbial community composition and associated change over time among three different backyard composting styles.

Food waste was composted in a household backyard compost bin, a small-scale aerated windrow or a semi-aerated static pile. Samples were obtained from each sequential phase of the composting process for 16s rRNA sequencing and relationships between temperature, moisture and microbial communities were examined. The Bacilli dominated in the early phases of composting then transitioned to Proteobacteria in the later stages. Different bacterial species increased and decreased dramatically in different composting systems and at different phases of the composting process. We performed qPCR to quantify gene abundance of nirS to profile the nitrogen-metabolizing bacteria present in each composting system. Gene abundance of nirS varied with temperature, but peaked during the cooling phase in the aerated windrow.

Although the phases of decomposition were not as distinct as large-scale regulated piles, the microbial diversity mirrored the appropriate phases. Interestingly, different backyard composting styles were marked by the predominance of certain bacterial species. In particular, nitrogen-metabolizing bacterial communities peaked in the later stages of decomposition.

A profile of the compost microbiome yields important clues about how differences in backyard food waste composting systems influence bacterial species that may facilitate or hinder nitrogen metabolism.