Table 2.

Effects of salt stress and unlabeled analogs on the uptake of [14C]DMSP, [14C]DMSA, and [14C]GB by S. meliloti 102F34a

Onium suppliedbUptake rateb (nmol/min/mg of protein)% Inhibition of uptake by unlabeled analogs at different competitor/substrate ratiosd
GBDMSADMSP
Control cultureStressed culturec1:110:11:110:11:110:1
[14C]DMSP6.115 NDe 99ND95ND80
[14C]DMSA8.532799747842743
[14C]GB1238508024561022
  • a Cultures were grown and uptake experiments were performed in LAS minimal medium (unstressed control culture) or in LAS containing 0.5 M NaCl (stressed culture).

  • b Uptake rates were determined as described in the text in the early exponential phase of growth (OD570, 0.3).

  • c Similar uptake rates were observed in stressed cultures grown in LAS medium containing isoosmotic concentrations of KCl (0.5 M) or K2SO4 (0.4 M).

  • d The results are expressed as percentages of reduction compared with uninhibited transport rates which were observed in a stressed culture. Similar levels of inhibition were observed in unstressed (control) cells (data not shown).

  • e ND, not determined.