Environmental modulators of algae-bacteria interactions at scale

Abstract

Photosynthetic microbes associated with non-photosynthetic, heterotrophic, bacteria play a key role in the global primary production. Understanding these phototroph-heterotroph associations is therefore important, but remains challenging because they reside in chemically complex aquatic and terrestrial environments. We do not understand how the myriad of environmental parameters from nutrient availability to pH impact interactions between phototrophs and their heterotrophic partners. Here, we leverage a massively parallel droplet microfluidic platform that enables us to interrogate algae-bacteria interactions in >100,000 communities across [~]525 environmental conditions with varying pH, carbon availability and phosphorous availability. By developing a statistical framework to dissect interactions in this complex dataset, we reveal that dependance of algae-bacteria interactions on nutrient availability is strongly modulated by pH and buffering capacity. Furthermore, we show that the chemical identity of the available organic carbon source controls how pH, buffering capacity, and nutrient availability modulate algae-bacteria interactions. By leveraging a high-throughput platform, our study reveals the previously underappreciated role of pH in modulating phototroph-heterotroph interactions.