Genetic characterization of oligopeptide uptake systems inSinorhizobium meliloti

Abstract

The genetic characterization of three ABC transport systems involved in oligopeptide uptake by Sinorhizobium meliloti is reported. Oligopeptide permease (Opp) encoded by the pSymB oppABCD operon, is required for uptake of tetrapeptides and certain tripeptides like 3Ala and bialaphos. The chromosomally encoded dipeptide permease (Dpp1), also able to import the toxic tripeptide bialaphos, is required for utilization of dipeptides and tripeptides like 3Gly and GlyGlyAla, with minor importance for utilization of 3Ala and tetrapeptides. The ttp (tri and tetrapeptide uptake) operon, encodes a third ABC system (Ttp) unable of transporting bialaphos and with minor role in the utilization of tetrapeptides and tripeptides like 3-Ala. Despite the overlapping substrate specificities of these ABC transporters, the corresponding gene operons displayed distinct expression profiles: dpp1 showed high constitutive expression levels under all conditions tested, in contrast to the low expression levels of ttp, whereas opp was maximally expressed upon entry into stationary phase. Nevertheless, complex interactions among the three systems at the transcriptional level were observed: opp was negatively autoregulated via OppA and positively regulated via DppA1, whereas dpp1 seems negatively autoregulated via DppA1. The expression of both opp and dppl was reduced in Ttp mutants. The ABC transport systems characterized in this work are not essential for the establishment of nitrogen-fixing symbiosis with alfalfa.

Quantitative Proteomic Analysis of the Hfq-Regulon in Sinorhizobium meliloti 2011

“…Several components of ABC transport systems possibly involved in uptake of oligopeptides were accumulated in the hfq mutant (Table S2): DppA1 (SMc00786), DppA2 (SMc01525), DppD2 (SMc01528) and DppF2 (SMc01529) are part of dipeptide transporters [53]; OppA (SMb21196) has been identified as a periplasmic binding component of an ABC transport system for di- and tripeptides [53]; all proteins encoded by the aap operon ( aapJQMP ; SMc02121, SMc02120, SMc02119, SMc02118), constitute a high affinity transport system for L-amino acids [41]; and several genes of the liv operon ( livHMGFK ; SMc01946, SMc01948, SMc01949, SMc01950, SMc01951) [41], are involved in the high affinity transport of leucine, valine and isoleucine. Several of the proteins encoded by these operons related to uptake of amino acid and small peptides were also previously reported to be negatively controlled by Hfq at either the protein or mRNA level [37], [38], [39] (Table S2), confirming the strong influence of Hfq on the flow of amino acids in S. meliloti .…”

Comparative Genomics of Cultured and Uncultured Strains Suggests Genes Essential for Free-Living Growth of Liberibacter

“…The structure and sequence of the L. crescens OppDABC operon is most similar to that of the alphaproteobacteria Roseobacter denitrificans OCh114. Mutants of Sinorhizobium meliloti in oppA and oppB exhibit impaired growth on minimal medium supplemented with tetra peptides [33]. In E. coli Opp mutants lyse more quickly than wild type cells once all diaminopimelic acid (DAP) in the growth medium is exhausted.…”

Riboregulation in Nitrogen-Fixing Endosymbiotic Bacteria

“…Thus, it is not surprising the large number of ABC (ATP-binding cassette) transporters encoded by rhizobial genomes [9,53,54]. Acquisition of amino acids (aa), peptides, metal ions, or sugars through ABC transporters impacts important cellular processes such as differentiation, virulence or conjugation [55].…”