Nutrient-dependent interactions between a marine copiotroph and a diatom .

As the major producers and consumers, phytoplankton and bacteria play central roles in marine ecosystems and their interactions show great ecological significance. Whether mutualistic or antagonistic, the interaction between certain phytoplankton and bacterial species is usually seen as a derivative of intrinsic physiological properties and rarely changes. This study demonstrated that the interactions between the ubiquitously co-occurring bacteria and diatom, and , varied with nutrient conditions. They overcame hardship together in oligotrophic seawater but showed antagonistic effects against each other under nutrient amendment. The contact-dependent algicidal behavior of based on protease activity solved the paradox among bacterial proliferation, nutrient viability, and algal demise haunting other known non-contact-dependent algicidal processes and might actually trigger the collapse of algal blooms . The chemotactic and swarming movement of might also contribute greatly to the breakdown of "marine snow," which could redirect the carbon sequestration pathway in the ocean.