The ability of microorganisms to withstand long periods of nutrient starvation, and not die, is key to their survival and success under the fluctuating conditions common in nature. Therefore, one would expect starvation resistance to be prevalent among organisms in the nutrient-poor open ocean. Surprisingly, this is not the case for Prochlorococcus, the most abundant photosynthetic organism in the oceans, which is responsible for ~5% of global primary production. When starved for nutrients, Prochlorococcus die rapidly, yet they survive (at least under laboratory conditions) when they interact with some co-occurring heterotrophic bacteria. In this talk, I will describe how we combine laboratory experiments, bioinformatic analyses and mathematical models at different levels of complexity to better understand mortality in Prochlorococcus, and how it is affected by microbial interactions. Our results highlight the lack of fundamental understanding of the process of cell death, which we propose is a major “black box” in microbial physiology and ecology.