Prochlorococcus can use the Pro1404 transporter to take up glucose at nanomolar concentrations in the Atlantic Ocean

Abstract

Prochlorococcus is responsible for a significant part of CO2 fixation in the ocean. Although it was long considered an autotrophic cya- nobacterium, the uptake of organic compounds has been reported, assuming they were sources of limited biogenic elements. We have shown in laboratory experiments that Prochlorococcus can take up glucose. However, the mechanisms of glucose uptake and its occur- rence in the ocean have not been shown. Here, we report that the gene Pro1404 confers capability for glucose uptake in Prochlorococcus marinus SS120. We used a cyanobacterium unable to take up glu- cose to engineer strains that express the Pro1404 gene. These recombinant strains were capable of specific glucose uptake over a wide range of glucose concentrations, showing multiphasic trans- port kinetics. The Ks constant of the high affinity phase was in the nanomolar range, consistent with the average concentration of glu- cose in the ocean. Furthermore, we were able to observe glucose uptake by Prochlorococcus in the central Atlantic Ocean, where glucose concentrations were 0.5–2.7 nM. Our results suggest that Prochlorococcus are primary producers capable of tuning their metabolism to energetically benefit from environmental conditions, taking up not only organic compounds with key limiting elements in the ocean, but also molecules devoid of such elements, like glucose