The Bacteroid Periplasm in Soybean Nodules Is an Interkingdom Symbiotic Space

Abstract

The functional role of the periplasm of nitrogen-fixing bacteroids has not been determined. Proteins were isolated from the periplasm and cytoplasm of Bradyrhizobium diazoefficiens bacteroids and were analyzed using liquid chromatography tandem mass spectrometry proteomics. Identification of bacteroid periplasmic proteins was aided by periplasm prediction programs. Approximately 40% of all the proteins identified as periplasmic in the B. diazoefficiens genome were found expressed in the bacteroid form of the bacteria, indicating the periplasm is a metabolically active symbiotic space. The bacteroid periplasm possesses many fatty acid metabolic enzymes, which was in contrast to the bacteroid cytoplasm. Amino acid analysis of the periplasm revealed an abundance of phosphoserine, phosphoethanolamine, and glycine, which are metabolites of phospholipid metabolism. These results suggest the periplasm is a unique space and not a continuum with the peribacteroid space. A number of plant proteins were found in the periplasm fraction, which suggested contamination. However, antibodies to two of the identified plant proteins, histone H2A and lipoxygenase, yielded immunogold labeling that demonstrated the plant proteins were specifically targeted to the bacteroids. This suggests that the periplasm is an interkingdom symbiotic space containing proteins from both the bacteroid and the plant.

Site-specific cleavage of bacterial MucD by secreted proteases mediates antibacterial resistance in Arabidopsis

“…Alternatively, secreted SAP1 and SAP2 may also at least partly cleave MucD in the periplasm of Pto . Bacteria possess the ability to take up host proteins via membrane transporters 50–52 . Secreted SAP1 and SAP2 may exploit such systems to target MucD.…”

Proteomic Characterization of Bradyrhizobium diazoefficiens Bacteroids Reveals a Post-Symbiotic, Hemibiotrophic-Like Lifestyle of the Bacteria within Senescing Soybean Nodules

“…Bacteroids were isolated as described previously [17] and enzyme activities were performed on the same day. Cytoplasmic and periplasmic fractions were prepared as described previously [42]. Briefly, 30 g of bacteroids from each biological replicate were aliquoted into 10 g amounts and resuspended in 10 mL of 25 mM citrate buffer, pH 4.0.…”

Multidisciplinary approaches for studying rhizobium–legume symbioses

“…Similarly, comparing the proteomes of bacteroids isolated from naturally effective and ineffective symbioses implicates pathways contributing to symbiotic efficiency (Cooper et al 2018). The proteomes of the peribacteroid space and peribacteroid membrane (Saalbach et al 2002) and of the bacteroid periplasm (Strodtman et al 2017) have been determined, and the results suggest strong partitioning of proteins among these functionally distinct compartments (Strodtman et al 2017). Furthermore, nodule proteomics has been used to examine the proteome during field growth conditions (Delmotte et al 2010), to compare root nodules and stem nodules (Delmotte et al 2014), and to identify NifA-regulated proteins (Salazar et al 2010).…”