Interaction-specific changes in the transcriptome of Polynucleobacter asymbioticus caused by varying protistan communities

We studied the impact of protist grazing and exudation on the transcriptomic response of the prokaryotic prey species Polynucleobacter asymbioticus.Different single- and multi-species communities of chrysophytes were used to determine a species-specific response to the predators and the effect of chrysophytediversity. Therefore, we sequenced the mRNA of Polynucleobacter in communities with three single chrysophyte species and all combinations. It could be shownthat the molecular responses of P. asymbioticus significantly changed in the presence of predators with different trophic modes and combinations of species. In the single-species samples we observed significant differences related to the relative importance of grazing in the protist-bacteria interaction, i.e. to the presence of eitherthe heterotrophic Poteriospumella lacustris or the mixotrophic Chlorochromonasdanica. This brings about a change in the expression of genes acting in stressresponse, transcription and translation, iron transport and incorporation. Themolecular changes indicate a reduced growth and increased stress response of P.asymbioticus in the presence of P. lacustris. The presence of C. danica might belinked to conditions of iron-limitation and cause changes in the iron metabolismof P. asymbioticus. Additionally, we observe a benefit for P. asymbioticus from amore diverse protistan community, which could be due to a change to autotrophicgrowths in the mixotrophic chrysophytes when competing for food with otherspecies. The single-species samples show a lower abundance of bacteria as well ashints to nutritional limitations and thus no utilisation of photosynthetic exudatesfrom the chrysophyte species