Role of the RNA-binding protein Hfq in Serratia plymuthica.

The RNA-binding protein Hfq has been well studied as a global post-transcriptional regulator which controls diverse cellular processes in bacteria. However, the function in the genus of Serratia has remained unexplored. Here we show that beyond mutation in Hfq resulting in their growth defects, Hfq has global effects on a variety of biocontrol-related phenotypes in the endophytic strain G3 of Serratia plymuthica, including antifungal activity, production of exoenzymes, as well as motility and biofilm formation. Especially for the first time, Hfq is observed to control biosynthesis of auxin indole-3-acetic acid (IAA) and antibiotic pyrrolnitrin (PRN), which are key determinants responsible for plant growth promotion and suppression of phytopathogens, respectively by G3. Additionally, Hfq is also required for the production of RpoS, a major stress sigma factor in G3. In contrast to E. coli, translation of hfq in G3 is positively autoregulated. Further investigation of the molecular mechanisms involved in regulation of IAA and pyrrolnitrin production by Hfq and its role in the regulatory networks of G3 will help to optimize the beneficial plant-microbe interactions.