Pseudomonas and Plantibacter transcriptomes in response to Isothiocyanate
Plants produce a plethora of specialized metabolites that often play important roles in their defence against pathogenic microbes or herbivorous insects. Exposure of leaf colonizing microbes to these metabolites influences their growth, and we hypothesize that it also has consequences for microbe microbe interactions. In Brassicaceae plants like the model plant Arabidopsis thaliana, glucosinolates and their biologically active derivatives, the isothiocyanates, are major defence metabolites. Adapted plant pathogens like Pseudomonas spp. use the hydrolase SaxA to convert the antimicrobial isothiocyanate sulforaphane to a nontoxic amine, whereas non-adapted commensal microbes are inhibited by this plant toxin. We used an ITC senstivie Plantibacter strain as a model commensal in and a Pseudomonas viridiflava strain as a model ITC degrading opportuniistic pathogen to understand how they interact in the presence of ITCs. Both strains were isolated from the same wild A. thaliana population. Without isothiocyanate, Plantibacter grew better alone than with Pseudomonas, a potential competitor. At high isothiocyanate concentrations, however, the commensal was dependent on SaxA mediated isothiocyanate degradation in both solid and liquid medium. At intermediate isothiocyanate concentrations, Plantibacters transcriptome changed in response to sulforaphane in monoculture but not in coculture with Pseudomonas, suggesting that it was fully protected from this toxin. In return, Plantibacter caused transcriptional changes in Pseudomonas, suppressing biofilm formation and increasing amino acid metabolism gene expression which might suppress virulence and so contribute to plant health. Together, we find that degradation of an antimicrobial plant metabolite can protect a commensal to depend on a pathogen-produced virulence factor, suggesting effects on community composition in environments where microbes are exposed to ITCs.