Possible mechanisms underlying the slow lactose fermentation phenotype in Shigella spp.
A Southern hybridization analysis revealed that the region homologous to Escherichia coli lacZ was present on the chromosomal DNAs of beta-galactosidase-positive Shigella strains, such as Shigella dysenteriae serovar 1 and Shigella sonnei strains, whereas this region was absent from chromosomal DNAs of beta-galactosidase-negative strains of Shigella flexneri and Shigella boydii. We found that the lacY-A region was deficient in S. dysenteriae serovar 1 and believe that this is the reason for the slow fermentation of lactose by this strain. S. sonnei strains possessed the region which hybridized with E. coli lacY-A despite their slow hydrolysis of lactose. The whole lactose-fermenting region was cloned from S. sonnei and compared with the cloned lac operon of E. coli K-12. Both clones directed the synthesis of beta-galactosidase in an E. coli K-12 strain lacking indigenous beta-galactosidase activity (strain JM109-1), and we observed no difference in the expression of beta-galactosidase activity in S. sonnei and E. coli. However, E. coli JM109-1 harboring the lactose-fermenting genes of S. sonnei exhibited the slow lactose fermentation phenotype like the parental strain. S. sonnei strains had no detectable lactose permease activities. E. coli JM109-1 harboring the lactose-fermenting genes of S. sonnei had a detectable permease activity, possibly because of the multicopy nature of the cloned genes, but this permease activity was much lower than that of strain JM109-1 harboring the lac operon of E. coli K-12. From these results we concluded that slow lactose fermentation by S. sonnei is due to weak lactose permease activity.
Ito
H
H
Department of Bacteriology, Nagoya University School of Medicine, Aichi, Japan.
Kido
N
N
Arakawa
Y
Y
Ohta
M
M
Sugiyama
T
T
Kato
N
N
D015139:Blotting, Southern; D015153:Blotting, Western; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D015342:DNA Probes; D004269:DNA, Bacterial / Q000032:analysis; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D029968:Escherichia coli Proteins; D005285:Fermentation; D005798:Genes, Bacterial; D007763:Lac Operon; D007785:Lactose / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000502:physiology; D009004:Monosaccharide Transport Proteins; D010641:Phenotype; D012760:Shigella / Q000145:classification / Q000201:enzymology / Q000235:genetics*; D012762:Shigella dysenteriae / Q000145:classification / Q000201:enzymology / Q000235:genetics; D012764:Shigella sonnei / Q000145:classification / Q000201:enzymology / Q000235:genetics; D027981:Symporters; D001616:beta-Galactosidase / Q000378:metabolism
D015342:DNA Probes; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C050221:LacY protein, E coli; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D027981:Symporters; C021499:lactose permease; D001616:beta-Galactosidase; D007785:Lactose