What if some harmful algal blooms are triggered by certain kinds of bacteria? These bacteria, as the theory goes, spark algal blooms by helping algae acquire iron, which is often in short supply in the marine realm and is a prerequisite for cell growth. Consistent with this theory, chemists leading the project have isolated a group of bacteria, associated with phytoplankton worldwide, that produce vibrioferrin—a compound that binds to inorganic iron in seawater and then under sunlight degrades into a highly bioavailable iron form. Experiments show that after photolysis, iron uptake increases in bacteria and algae, suggesting that bacteria “share” their iron products with neighboring algae. Scientists are investigating the degree to which interactions between bacteria and algae facilitate nutrient acquisition and how this relates to primary productivity and harmful algal bloom formation.