In addition to causing global warming, anthropogenic emissions of CO2 are altering the chemistry of Earth’s seas and oceans, turning them more acidic. This change has important implications for many organisms, especially those whose shells or skeletons are made of calcium carbonate, like corals and shellfish. Strong efforts have been devoted to study the potential effects of acidification on these particular species demonstrating, in the majority of occasions, detrimental effects. However, acidification may also interfere with the development of marine bacteria (Fig. 1), which play a crucial role in the global cycle of elements necessary to life. Bacteria act as the primary degraders of organic material produced through photosynthesis of microscopic algae in the ocean, or material released through wastewater. When algae or other organisms die and are degraded by bacteria, at the same time bacteria mediate the release of elements like nitrogen or phosphorous that are essential to the food chain. Thus, bacteria in the sea play a critical role in determining the health of marine ecosystems. In addition, bacteria synthesize vitamins on which algae and other organisms in the sea depend. Despite these important roles, possible ocean acidification effects on marine bacteria have mostly been ignored or neglected. In order to tackle this issue, we performed a metatranscriptome analyses of a phytoplankton bloom mesocosm experiment conducted at Institut de Ciències del Mar with water from the Blanes Bay, north of Barcelona (Fig. 2). Our results demonstrated that marine bacteria exposed to acidification are indeed forced to significantly alter their metabolism. In particular, they respond to low pH by enhancing the expression of genes encoding proton pumps, such as respiration complexes, proteorhodopsin and membrane transporters. Thus, bacteria need to invest extra energy for activating mechanisms to counterbalance the stress produced by acidification. This study, conducted by researchers from Catalonia, Spain and Sweden, suggests that bacterioplankton adaptation to ocean acidification could have long-term effects on the energy balance of ocean ecosystems.