How natural dynamic pH conditions could affect compounds mediating marine diatom-bacteria interactions: a chemical theoretical perspective

Life in marine diatom-bacteria communities is coordinated through a multitude of chemically-mediated interactions in a highly dynamic environment. Respiration and photosynthesis create steep gradients and large fluctuations in abiotic conditions on diel timescales. But how sensitive biomolecules involved in microbial interactions are to such dynamic microscale environmental impacts has not been assessed so far. Here, I present a predictive chemical-theoretical framework to scope the scale of impact of pH on interactive compounds for representative planktonic and benthic microscale conditions. Focussed on a dataset of 131 compounds from diatom and bacteria interactions, theoretical analyses revealed a high degree of pH-sensitivity, potential links between sensitivity and specific functional chemical groups, differences for source and target organisms and in sensitivity between compounds performing different interactive roles. The predicted effects for some key metabolites matched diel dynamics reported in existing literature for mesocosm and field studies. pH could therefore be hypothesised as a significant factor in mediating chemical exchange and interactions in phototrophic-heterotrophic communities by directly altering diatom and bacteria signals and metabolites. This perspective highlights how microscale pH conditions could play an influential role and provides a framework to derive focussed, testable hypotheses to assess chemical impacts on marine microbial interactions in future experiments.