To investigate sodium-dependent growth, ‘sodium-free M9’ was prepared by replacing TSA HDAC cell line all sodium salts in M9 (this is around 50 mM Na+ in normal M9) with their potassium equivalents and replacing agar with 0.8% agarose; the sodium-free M9 medium still contained approximately 50 μM sodium from the Amp used for selection. M9 agarose plates required longer incubation
times (up to 4 days) for single colonies to grow. All experiments involving the WT and the ΔnanT strains used cells transformed with the empty vector, i.e. pWKS30. The presence of the vector did not affect the growth phenotypes of either strain (not shown). Starter cultures were prepared as described for the growth experiments, except that o/n growths were carried out in M9 Amp supplemented with 2 mg mL−1 glucose and 1 mM IPTG. Overnight cultures were diluted to an OD650 nm of 0.1 in the
same medium and allowed to grow at 37 °C until they reached an OD650 nm of 0.5, when they were harvested, washed four times in M9, resuspended in the same buffer at a final OD650 nm of 3 and stored www.selleckchem.com/btk.html on ice till use. For Neu5Ac uptake assays, cells were diluted 10-fold in M9 prewarmed at 37 °C and allowed to acclimatize for 2 min, with stirring before initiating the assays by adding of varying amounts of [14C]-Neu5Ac (Sigma) appropriately diluted with unlabelled Neu5Ac. The uptake assay and total protein quantification were then performed as described in Severi et al. (2008), except that 200 μL of cell suspensions were immobilized instead of 400 μL. [14C]-Neu5Ac was normally used at a final concentration of 0.5–2 μM and isotopically diluted (up to 100 ×) with unlabelled Neu5Ac when required. Ks and Vmax values were calculated by fitting the experimental data for uptake rates to a hyperbolic Michaelis–Menton equation using sigmaplot. To assay sodium-dependent Neu5Ac uptake, cells were prepared as for a standard uptake assay, except that sodium-free M9 (see the previous section) was used as both washing and
assay buffers. Salts, i.e. NaCl, KCl and LiCl, were added at a final Methane monooxygenase concentration of 100 mM during the acclimitization phase. The assay was performed as described above with a concentration of 100 μM total Neu5Ac. Cold chase experiments were performed as described in Mulligan et al. (2009), using SEVY1 cells transformed with the appropriate plasmids. To assess the suitability of an E. coliΔnanT strain for the functional characterization of hypothetical Neu5Ac transporters, we first examined cells expressing either nanT itself or the known siaPQM TRAP transporter genes from H. influenzae cloned into a low-copy-number vector under the control of an IPTG-inducible promoter.