Hydraulics is a key driver of microbial life in streams and rivers

A new study has found that hydraulics determines microbial lifestyles along streams and rivers, with important implications for river health, biodiversity, and water quality. In streams and rivers, bacteria, algae, and other microorganisms form tight-knit communities that feed the ecosystem, drive its biodiversity, and purify its water. These communities exist in several forms, swimming freely, clumping together, or as biofilms that attach to rocks and other surfaces. For the first time, a team of researchers has shown that the amount of turbulence the microorganisms are exposed to determines the form of their community. Their findings, published in the journal Nature Microbiology , have important implications for river health, biodiversity, and water quality. 'In streams, life-enabling energy comes in two currencies: dissolved organic carbon and sunlight. Both first have to be captured and transformed in order to become accessible to species that occupy the higher rungs of the food chain,' says Tom Battin, the senior author of the study. In nature, communities of microbes carry out this critical job. Flipping the switch 'After decades of thinking that these microbial communities existed predominantly as free-floating cells, we now understand that most microbial life in streams and rivers occurs as biofilms and aggregates,' says Battin. While free-swimming communities are most common in open water, biofilms are found mainly in turbulent water. Aggregates tend to form anywhere in between. Robert Niederdorfer, PhD in Battin lab and first-author of the study, set out to determine what drove the communities to take on a specific lifestyle. Did random chance dictate which bacterial species, and consequently, which lifestyle would prevail?