I am a microbiologist and my primary interest is to understand how microbes interact with each other in the ocean. A fundamental question is how do bacteria accumulate sufficient nutrients to enable growth when, in the oligotrophic ocean, nutrients are present at incredibly low concentrations? Over a period of a day, molecular diffusion could provide sufficient nutrients to support a doubling time of one day for heterotrophic bacteria and autotrophic cyanobacteria. It is unclear how bacteria assimilate low molecular weight compounds against a steep concentration gradient; nutrient concentrations will be many orders of magnitude greater within the cell than in the water in which the bacteria are growing.