Further stabilization of 3-isopropylmalate dehydrogenase of an extreme thermophile, Thermus thermophilus, by a suppressor mutation method.

We succeeded in further improvement of the stability of 3-isopropylmalate dehydrogenase (IPMDH) from an extreme thermophile, Thermus thermophilus, by a suppressor mutation method. We previously constructed a chimeric IPMDH consisting of portions of thermophile and mesophile enzymes. The chimeric enzyme is less thermostable than the thermophile enzyme. The gene encoding the chimeric enzyme was subjected to random mutagenesis and integrated into the genome of a leuB-deficient mutant of T. thermophilus. The transformants were screened at 76 degrees C in minimum medium, and three independent stabilized mutants were obtained. The leuB genes from these three mutants were cloned and analyzed. The sequence analyses revealed Ala-172-->Val substitution in all of the mutants. The thermal stability of the thermophile IPMDH was improved by introducing the amino acid substitution.

Screening for bacteriuria in healthy Japanese school children.

Bacteriuria was screened among 28,202 healthy school children, 14,575 boys and 13,627 girls by dipstick and dipslide methods and also by pour plate culture method. Prevalence of bacteriuria was 0.06% in boys and 0.54% in girls after third screening. A high rate of false negative results with dipstick test and a high rate of false positive results with dipslide culture method using Microstix-3 were observed. About 60% of screened children continued to have bacteriuria persistently for 9 months after third screening followed by monthly urine culture. Anomalies of urinary tract were detected in 9 of 26 children with persistent bacteriuria.