Interactions between marine phytoplankton, viruses, and bacteria drive biogeochemical cycling, shape marine trophic structures, and impact global climate. These interactions are mediated by excreted small compounds – infochemicals – which can impact microbial physiology and community structure. This work aims to reveal the biomolecular mechanism of one such interaction, in which the bacterial quorum sensing molecule 2-heptyl-4-quinolone (HHQ) produced by the marine bacterium Pseudoalteromonas sp. arrests cell division and confers protection against virus-induced mortality in the globally abundant phytoplankton Emiliania huxleyi. Here, we investigate whether HHQ inhibits an enzyme critical for nucleotide biosynthesis – dihydroorotate dehydrogenase (DHODH) – in E. huxleyi, which may explain many of the physiological and metabolic changes induced in E. huxleyi by HHQ. Preliminary evidence supports inhibition of E. huxleyi DHODH (EhDHODH) by HHQ, with 10 uM HHQ being sufficient to significantly reduce endogenous DHODH activity in E. huxleyi cell lysate. The specifics of HHQ's impact on EhDHODH will be further quantified by precisely assaying activity of pure, recombinant EhDHODH exposed to HHQ, yielding an IC50 and a kinetic profile of the inhibited enzyme. By characterizing the mechanisms by which bacterial signals influence phytoplankton physiology and virus-induced mortality, we enhance our ability to decode the chemical crosstalk of marine microorganisms, thereby strengthening our ability to make predictions about the global ecological processes these microorganisms influence.

Primary Presenter: Oscar Garrett, Haverford College (ogarrett@haverford.edu)

Authors:

Oscar Garrett, Haverford College  (ogarrett@haverford.edu)

Kristen Whalen, Haverford College  (kwhalen1@haverford.edu)