THE QUORUM-SENSING MOLECULE 2-HEPTYL-4-QUINOLONE (HHQ) INFLUENCES THE COMMUNITY COMPOSITION OF MARINE MICROBES

Population dynamics among marine microbes impact the cycling of nutrients and are often chemically mediated. Recently, 2-heptyl-4-quinolone (HHQ), a quorum-sensing molecule produced by the marine bacterium Pseudoalteromonas piscicida, was shown to arrest the growth of the coccolithophore Emiliania huxleyi. To further explore the role of HHQ in structuring microbial populations, 16S and 18S amplicon sequence data were generated from HHQ-spiked microcosms using water from a nutrient-stimulated phytoplankton bloom on the coast of Bergen, Norway in 2017. Both the free-living and particle-associated microbial communities changed over time as eukaryotic phytoplankton responded to nutrient-stimulation. In addition, treatment of mesocosm water with HHQ at ecologically relevant concentrations resulted in significant shifts in bacterial community structure. In both the free-living and the particle-associated community, many Flavobacteria subgroups decreased in relative abundance when treated with HHQ. This coincided with an increase in the relative abundance of many Alphaproteobacteria (Rhodobacteria) and Gammaproteobacteria subgroups including Pseudoalteromonas spp., which have been documented to produce HHQ. Overall, these findings suggest quorum sensing molecules like HHQ may play a broader role in regulating polymicrobial interactions than previously recognized. Controlled laboratory experiments are being conducted to confirm the effects of HHQ on the absolute abundance of different marine microbes and to explore the molecular substrates of those potential interactions.