The synthesis of β-galactosidase in Rhizobium meliloti WU60 was found to be inducible by lactose and its non-metabolizable analogue. isopropyl-β-ᴅ-thiogalactoside (IPTG). In contrast to Escherichia coli, galactose and melibiose were very weak inducers of this enzyme in R. meliloti. The maximum level of β-galactosidase in this bacterium is 2% of that in fully induced E. coli. In addition to glucose, the induced synthesis of this enzyme in R. meliloti was repressed by galactose, glycerol, and succinate. In comparison to E. coli, addition of cyclic AMP to the growth medium of R. meliloti did not alleviate the repressive effect of the above compounds on β- galactosidase synthesis.
High concentrations of sodium succinate (100 mᴍ) were inhibitory to the growth of R. meliloti. Spontaneous succinate-resistant mutants could be isolated at low frequency. In contrast to the wild type parent, in a succinate-resistant mutant, the synthesis of β-galactosidase was not repressed by succinate.
The present paper deals with the kinetics of oxidation of D-galactose by Nessler's reagent in alkaline medium. The reaction is zero order with respect to Hg(II) and first order with respect to reducing sugar. The direct proportionality of the reaction rate at low hydroxide ion concentrations shows retarding trend at higher concentrations. The reaction rate is inversely proportional to iodide ion concentration. A mechanism has been proposed taking HgI3- as the reacting species