Synechococcus as an HOOH-Consuming Helper for Prochlorococcus

The marine cyanobacterium Prochlorococcus is an abundant and globally important microbe that contributes an estimated 40% of bacterial production in the oligotrophic ocean. The success of this photosynthetic bacterium is largely a consequence of its small cell size and streamlined genome, which are advantageous in nutrient-limited environments. However, this genomic streamlining has also led to the loss of the gene (katG) encoding catalase, an enzyme that is essential for the degradation and detoxification of the reactive oxygen species hydrogen peroxide (HOOH). HOOH is naturally present in the illuminated waters of the ocean, and in the absence of catalase, Prochlorococcus is vulnerable to the cell-damaging and potentially lethal effects of HOOH-related oxidative stress. Previous work has demonstrated that catalase-positive heterotrophic members of the marine microbial community – termed “helpers” – can facilitate the growth of Prochlorococcus by removing HOOH from their shared environment. The present study investigates whether Synechococcus, a catalase-positive cyanobacterium closely related to and often found alongside Prochlorococcus, is also able to serve as a helper to Prochlorococcus by consuming HOOH that is present in shared culture medium. The characterization of this interaction provides insight into the ecological relationship between these two numerically dominant cyanobacteria