Overproduction of the rhizobial adhesin RapA1 increases competitiveness for nodulation

Competition for nodulation is a complex problem where bacterial adhesins, which are required for root colonization, may play a role. However, the possible influence of adhesins on competitiveness was scarcely studied. In this work, the Rhizobium leguminosarum bv trifolii adhesion protein RapA1 was overproduced from a pHC60-derived plasmid and expressed in R200 strain. When an overproducing strain and a control-carrying empty vector were co-inoculated on clover plants, a positive effect of RapA1 on competition for nodule occupation was observed. Therefore, optimization of RapA1 expression may be considered for improvement of rhizobial competitiveness.