Strikingly, Unknown taxa occurred as top hubs in all environments, suggesting that “microbial dark matter” play necessary ecological roles within their respective communities.
When the Unknown taxa were excluded from the networks, a significant reduction in degree and betweenness was observed for all environments. For each environment, we constructed networks including and excluding unknown organisms at multiple taxonomic levels and used network centrality measures to quantitatively compare networks. Here, we establish a method to study the ecological significance of “microbial dark matter” by building microbial co-occurrence networks from publicly available 16S rRNA gene sequencing data of four extreme aquatic habitats. To understand the ecological contributions of these Unknown taxa, it is essential to first understand the relationship between unknown species, neighboring microbes, and their respective environment. These unknown microbes, often referred to as “microbial dark matter,” represent a major challenge for biology. Microbes compose most of the biomass on the planet, yet the majority of taxa remain uncharacterized.
