Possible mechanisms underlying the slow lactose fermentation phenotype in Shigella spp

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Beta-galactosidase is crucial for lactose fermentation in bacteria.
• Shigella species exhibit varying abilities to ferment lactose.
• The genetic basis for lactose fermentation differences in Shigella is not fully understood.

Purpose of the Study:

• To investigate the genetic basis of lactose fermentation in Shigella species.
• To compare the lactose-fermenting genes of Shigella sonnei with Escherichia coli.
• To determine the role of beta-galactosidase and lactose permease in Shigella lactose fermentation.

Main Methods:

• Southern hybridization analysis to detect lacZ homologous regions.
• Cloning of the lactose-fermenting region from Shigella sonnei.
• Gene expression analysis in Escherichia coli K-12 strain JM109-1.
• Assay of beta-galactosidase and lactose permease activities.

Main Results:

• Beta-galactosidase-positive Shigella strains possess a lacZ homologous region, absent in negative strains.
• Shigella dysenteriae serovar 1 showed deficiency in the lacY-A region, correlating with slow lactose fermentation.
• Shigella sonnei possesses the lacY-A region but exhibits slow lactose fermentation and undetectable lactose permease activity.
• Cloned Shigella sonnei lactose-fermenting genes directed beta-galactosidase synthesis in E. coli but resulted in slow lactose fermentation and low permease activity.

Conclusions:

• Slow lactose fermentation in Shigella sonnei is attributed to weak lactose permease activity.
• The lacZ gene is present in beta-galactosidase-positive Shigella, but permease activity is the rate-limiting factor for fermentation in S. sonnei.
• Genetic analysis reveals differences in lactose metabolism pathways among Shigella species.