Aerobic bacteria produce nitric oxide via denitrification and promote algal population collapse

Microbial interactions govern marine biogeochemistry. These interactions are generally considered to rely on exchange of organic molecules. Here we report on a novel inorganic route of microbial communication, showing that algal-bacterial interactions between Phaeobacter inhibens bacteria and Gephyrocapsa huxleyi algae are mediated through inorganic nitrogen exchange. Under oxygen-rich conditions, aerobic bacteria reduce algal-secreted nitrite to nitric oxide (NO) through denitrification, a well-studied anaerobic respiratory mechanism. The bacterial NO is involved in triggering a cascade in algae akin to programmed cell death. During death, algae further generate NO, thereby propagating the signal in the algal population. Eventually, the algal population collapses, similar to the sudden demise of oceanic algal blooms. Our study suggests that the exchange of inorganic nitrogen species in oxygenated environments is a potentially significant route of microbial communication within and across kingdoms.

Automated summary

Microbial interactions in marine environments are believed to mainly rely on the exchange of organic molecules. However, our study reveals a novel inorganic route of microbial communication between algal and bacterial communities, mediated through inorganic nitrogen exchange. Aerobic bacteria reduce algal-secreted nitrite to nitric oxide (NO) via denitrification, triggering a cascade in algal cells similar to programmed cell death. The algae further generate NO during death, propagating the signal within the algal population. This exchange of inorganic nitrogen species in oxygenated environments may serve as a significant means of microbial communication across different kingdoms.