The bacterial signal HHQ disrupts phytoplankton-virus interactions

In the ocean, interactions between microbes can significantly influence biogeochemical cycles and ecosystem function. Cell-cell interactions are mediated by a myriad of factors, including chemical signaling. Recently, the quorum-sensing compound 2-heptyl-4-quinolone (HHQ), isolated from the marine gammaproteobacteria, Pseudoalteromonas piscicida, has been found to disrupt cell division in the coccolithophore, Emiliania huxleyi. To better understand the potential ramifications of this cell cycle arrest, a series of experiments were conducted that explored the impact of HHQ exposure on E. huxleyi-virus interactions. In short-term assays with three E. huxleyi virus (EhV) strains (207, 99B1, 163), the presence of HHQ significantly decreased virus-induced cell lysis of E. huxleyi, irrespective of EhV virulence. In a long-term experiment with EhV 163, HHQ exposure significantly decreased the intracellular and free viral concentrations relative to no HHQ controls. Interestingly, when EhV 163 were directly exposed to HHQ, not in the presence of E. huxleyi, viral concentrations were relatively unchanged. This suggests that HHQ does not damage viruses directly, however, it is likely that the arrest of the algae’s cell cycle influences the ability of EhVs to replicate. These results offer tantalizing evidence for a quorum-sensing compound potentially serving as a mechanism of protection against virus-induced mortality, thereby influencing the overall success of E. huxleyi and impacting nutrient cycling in the ocean.