Qualitative changes in proteins contained in outer membrane vesicles produced by Rhizobium etli grown in the presence of the nod gene inducer naringenin.

Abstract

In this work, we compared the proteomic profiles of outer membrane vesicles (OMVs) isolated from Rhizobium etli CE3 grown in minimal medium (MM) with and without exogenous naringenin. One-hundred and seven proteins were present only in OMVs from naringenin-containing cultures (N-OMVs), 57 proteins were unique to OMVs from control cultures lacking naringenin (C-OMVs) and 303 proteins were present in OMVs from both culture conditions (S-OMVs). Although we found no absolute predominance of specific types of proteins in the N-, C- or S-OMV classes, there were categories of proteins that were significantly less or more common in the different OMV categories. Proteins for energy production, translation and membrane and cell wall biogenesis were overrepresented in C-OMVs relative to N-OMVs. Proteins for carbohydrate metabolism and transport and those classified as either general function prediction only, function unknown, or without functional prediction were more common in N-OMVs than C-OMVs. This indicates that naringenin increased the proportion of these proteins in the OMVs, although NodD binding sites were only slightly more common in the promoters of genes for proteins found in the N-OMVs. In addition, OMVs from naringenin-containing cultures contained nodulation factor.