used, the ratio of carbonate and bicarbonate is chosen in such a way as to provide
both the optimal sodium and pH. A chloride-free carbonate buffered with an optimal
concentration of Na
+ medium can be used to determine the strain’s requirement for
chloride. Similar to a carbonate-free medium, up to five successive transfers on this
medium are usually enough to discern whether the strain requires chloride or not.
Fig. 3 Experimental setup for pouring anaerobic medium with simultaneous measurement and
setting the pH value. Arrows show: (a) A 1 L conical flask with a welded glass port (for mounting
the pH electrode; made in glass-blowing workshop) placed on a magnetic stirrer. (b) A rubber
stopper with three holes for three tubings: two for supplying nitrogen and titrants, the third for
pouring the medium into a Hungate tube. (c) A plastic medical syringe with a connected narrow
polypropylene tubing (inner diameter is ca. 1 mm; used in liquid chromatography) to accurately
dispense titrants (concentrated HCl or NaOH) to the bulk of the medium
Isolation and Cultivation of Alkaliphiles
73