In terms of environmental and economic impact, the Columbia River is the most important river in the US Pacific Northwest.
To characterize the microbial diversity within its estuary, Holly M. Simon and colleagues from Oregon Health & Science University's Center for Coastal Margin Observation and Prediction and the J. Craig Venter Institute, sequenced total DNA from water in four habitats: the Columbia River's immediate outflow; the river plume that extends into Pacific Ocean; upwelling low-oxygen water off the coast; and the ocean bottom.
They show that the Columbia River estuary is a complex region characterized by high turbidity ("cloudiness"), in which bacteria attached to solid particles suspended in the water are crucial for recycling organic matter.
Paradoxically, the turbidity blocks sunlight in these estuarine waters and makes it difficult for photosynthetic algae to grow there, yet light-dependent bacteria dominate these waters. These bacteria are known as photoheterotrophs because they use both organic substrates and light energy for growth and survival.
They employ a protein that is related to light-sensitive pigments in mammalian eyes to generate energy from light, which helps them survive when nutrients are scarce. Habitat diversity, in the form of local variation in size and type of suspended particles, maintains the considerable bacterial biodiversity in the estuary of the Columbia River.