Analysis of an L-histidinol-utilizing mutant of Pseudomonas aeruginosa

Transductional analysis was applied to the Pseudomonas aeruginosa mutant PAO14 (hnc-1). This mutant can utilize L-histidinol as sole source of carbon and nitrogen and has a 60-fold increased histidinol dehydrogenase (HDH) content (Dhawale, Creaser & Loper, 1972). Transductional analysis was carried out using 18 histidine-requiring mutants to see where the hnc-1 locus maps in relation to the structural genes of histidine biosynthesis. The hnc-1 marker cotransduced with group IV genes at 97 to 100 % and not at all with group I, which is known to be the structural gene for HDH. The data obtained in the studies of Km (histidinol) and Km (NAD), and the effect of pH and temperature on the HDH activity from PAO1 and PAO14 are in full agreement with the genetic data that the hnc-1 mutation is not in the structural gene for HDH. It is suggested that hnc-1 may be a mutation in a regulatory gene affecting HDH synthesis in PAO14 and may map close to his-IV whose function in histidine biosynthesis is not known.