Microorganisms in streambeds play a crucial role in nutrient cycling and energy flow. A study looked at microbial communities in stream sediments from two watersheds and found that the structure of these communities is influenced by factors like the abundance of microeukaryotic photoautotrophs and environmental conditions. The smallest headwater streams within a watershed showed the most variation in microbial biomass. The composition of these microbial communities is not random and is affected by the presence of microeukaryotic photoautotrophs, environmental differences, and geographical distance.