Assessing Potential for Chromatic Acclimation in Oxygen Deficient Zone Synechococcus

Abstract

Synechococcus are a genus of ubiquitous marine cyanobacteria that play an important role in global carbon cycling. Synechococcus are abundant in oxygen deficient zones (ODZs)—expanding areas of the ocean where oxygen concentrations drop below 10 nM O2—where they fix carbon and introduce trace amounts of oxygen through photosynthesis to fuel aerobic respiration. Synechococcus can be grouped into different pigment types based on the makeup of the phycobilisome, a photosynthetic light-harvesting complex. Marine Synechococcus are predominantly either blue-light specialists, green-light specialists, or light-generalists. Light generalists undergo a process called chromatic acclimation where their phycobilisome structure is modified in response to changing light conditions allowing maximal growth under different colors of light which provides an advantage as a photosynthetic cell is moved throughout the upper water column. In this study, I use 10 strains of Clade 1 and CRD1 Synechococcus isolates and metagenomic data to determine the abundance, diversity, and potential for chromatic acclimation of Synechococcus in the Eastern Tropical North Pacific (ETNP) ODZ. I performed growth experiments on the Synechococcus isolates under white, blue, and green light finding that seven of the strains were able to chromatically acclimate while three were blue-light specialists. Through phylogenetic analysis, I found that Synechococcus in the ETNP ODZ fall into eight distinct groups that constitute 2 – 17% of the microbial community in the upper 50 meters of the water column. These results indicate that Synechococcus capable of chromatic acclimation are present and possibly abundant in the ETNP ODZ, comprising a potentially important contribution to cryptic oxygen cycling supporting aerobic heterotrophic communities.