| Highly localized concentrations of organic matter can have a strong effect on biodiversity, especially embedded within systems characterized by poor nutrient availability. Numerous studies have shown that these nutrient islands are important for surrounding communities because of the concentration of otherwise scare resources. In a notable example, the leaf-cutter ant Atta colombica deposit considerable amounts of waste material in concentrated locations on the forest floor. Refuse material accumulates over a colonies and contains significantly greater amounts of many important nutrients compared to surrounding soil. These somewhat stable and highly localized depositions of organic matter may have important consequences for the establishment of unique microbial communities and ultimately evolutionary specialization. In this dissertation I explore the structural, compositional, and functional potential, of leaf-cutter ant refuse dumps. In Chapter 2, I compare community structure of fungus gardens and refuse dumps using microbial membrane lipid analysis and find that gardens contain simple communities, dominated by Gram-negative bacteria. In contrast, dumps are diverse and enriched for Gram-positive bacteria. Clustering analyses reveal that community similarity reflects system component (gardens/dumps) rather than other factors. In Chapter 3, I explore microbial community composition of wild refuse dumps, and compare these communities to other environments. Using full-length and pyrotag 16S rRNA analysis, I show that these habitats contain a diverse and distinct microbiota, dominated by Actinobacteria, Bacteroidetes, and Proteobacteria. I also show that numerous taxa change significantly between upper and lower strata, suggesting potential succession in community structure. Finally in Chapter 4, I use community metagenomics to explore the functional content of leaf-cutter ant dump communities, specifically the potential for plant biomass degradation. I find that the refuse dump microbiome is composed of a diverse community with high plant biomass-degrading potential. Comparison of this microbiome's predicted proteome with other metagenomes shows closest similarity to compost, indicating evolutionary convergence between two distinct waste management systems. This work represents a first step in understanding the role microbial communities' play in degrading recalcitrant plant biomass within a natural and ancient composting system and highlights the potential of refuse dumps as a model for exploring fundamental processes in microbial ecology. |
