A new framework to interrogate molecular mechanisms mediating antagonistic diatom-bacteria interactions

Interactions between phytoplankton and bacteria play key roles in mediating carbon and nutrient fluxes in the oceans, yet the mechanistic basis and environmental impacts of such interactions are poorly understood. DIACIDAL addresses crucial unknowns in our understanding of the interactions of one of the most globally abundant phytoplankton, the diatoms, and their bacterial pathogens. This proposal builds on my teams recent advances developing an innovative sampling pipeline to isolate environmentally relevant bacterial pathogens of diatoms. This work suggests that bacterial pathogenicity towards diatoms is more prevalent than recognised previously. Moreover, we have important new evidence that diatoms can sense bacterial pathogens to evade their attack. Our new framework will be coupled with cutting-edge molecular tools that I have pioneered to study diatom signalling, including biosensors to track real-time signalling responses in single diatom cells. These tools have already made important breakthroughs in our understanding of how diatoms sense their environment. Exploiting these advances, we will use culture-dependent (Tn-Seq, comparative omics, and imaging) and new single-cell culture-independent approaches. By focussing on a model interaction, we will decipher mechanisms mediating bacterial pathogenicity towards diatoms, and elucidate how diatoms sense and evade their pathogens. This will reveal novel effectors and defence signalling systems. Finally, we will leverage the new tools and insights to quantify the prevalence of bacterial pathogenicity and diatom defence in natural ecosystems. This innovative, multidisciplinary program will advance understanding of mechanisms governing bloom dynamics, inform ecosystem models, and shed light on a poorly characterised environmental stressor confronting phytoplankton communities. This also has potential to unlock new translational opportunities for biotechnology e.g. novel antimicrobial and anti-fouling compounds.