Rhizobium tropici forms @entity1568 -fixing nodules on the roots of the common bean ( @entity11297 ). Like other legume-Rhizobium symbioses, the bean-R. tropici association is sensitive to the availability of @entity1391 (P(i)). To better understand @entity3151 movement between the bacteroid and the host plant, P(i) transport was characterized in R. tropici. We observed two P(i) transport systems, a high-affinity system and a low-affinity system. To facilitate the study of these transport systems, a Tn5B22 transposon mutant lacking expression of the high-affinity transport system was isolated and used to characterize the low-affinity transport system in the absence of the high-affinity system. The K(m) and V(max) values for the low-affinity system were estimated to be 34 +/- 3 microM P(i) and 118 +/- 8 nmol of P(i) x min(-1) x mg (dry weight) of cells(-1), respectively, and the K(m) and V(max) values for the high-affinity system were 0.45 +/- 0.01 microM P(i) and 86 +/- 5 nmol of P(i) x min(-1) x mg (dry weight) of cells(-1), respectively. Both systems were inducible by P(i) starvation and were also shock sensitive, which indicated that there was a periplasmic binding-protein component. Neither transport system appeared to be sensitive to the proton motive force dissipator @entity6320 , but P(i) transport through both systems was eliminated by the ATPase inhibitor @entity18040 ; the P(i) transport rate was correlated with the intracellular @entity855 concentration. Also, P(i) movement through both systems appeared to be unidirectional, as no efflux or exchange was observed with either the wild-type strain or the mutant. These properties suggest that both P(i) transport systems are ABC type systems. Analysis of the transposon insertion site revealed that the interrupted gene exhibited a high level of homology with kdpE, which in several bacteria encodes a cytoplasmic response regulator that governs responses to low @entity972 contents and/or changes in medium osmolarity.

Characterization of two inducible XXXX transport systems in Rhizobium tropici.

@entity11297 :: ('3885', 'Species') :: ['Phaseolus vulgaris'] @entity1568 :: ('MESH:D009584', 'Chemical') :: ['nitrogen'] @entity6320 :: ('MESH:D002258', 'Chemical') :: ['carbonyl cyanide m-chlorophenylhydrazone'] @entity18040 :: ('CHEBI:53090', 'Chemical') :: ["N,N'-dicyclohexylcarbodiimide"] @entity1391 :: ('CHEBI:26020', 'Chemical') :: ['phosphate'] @entity972 :: ('MESH:D011188', 'Chemical') :: ['potassium'] @entity3151 :: ('MESH:D010758', 'Chemical') :: ['phosphorus'] @entity855 :: ('MESH:D000255', 'Chemical') :: ['ATP']
@entity1391 :: (CHEBI:26020,Chemical) :: ['phosphate']
