CMP-KDO-synthetase activity in Escherichia coli expressing capsular polysaccharides

Area of Science:

• Microbiology
• Bacterial Physiology
• Biochemistry

Background:

• Escherichia coli produces various capsular polysaccharides, classified into groups.
• Group II capsular polysaccharide expression is known to be temperature-regulated.
• The molecular mechanisms underlying this temperature regulation require further elucidation.

Purpose of the Study:

• To investigate the role of CMP-KDO synthetase activity in temperature-regulated capsule expression in Escherichia coli.
• To determine if CMP-KDO concentration is a critical factor for group II capsule synthesis.
• To differentiate between temperature-regulated and non-regulated capsule expression in E. coli.

Main Methods:

• Culturing E. coli strains at different temperatures (18°C and 37°C).
• Assessing CMP-KDO synthetase activity in cytoplasmic and membrane fractions.
• Analyzing capsule expression in relation to CMP-KDO levels and temperature.

Main Results:

• Elevated CMP-KDO synthetase activity, linked to increased CMP-KDO concentration, was observed in cytoplasmic fractions of E. coli grown at 37°C, correlating with group II capsule expression.
• This temperature-dependent regulation and reliance on CMP-KDO was specific to group II capsules, not observed in group I.
• Some E. coli strains with group II-like capsules exhibited no temperature regulation or dependence on elevated CMP-KDO, suggesting a potential new classification (group I/II).

Conclusions:

• CMP-KDO concentration, regulated by CMP-KDO synthetase activity, is crucial for temperature-dependent expression of Escherichia coli group II capsular polysaccharides.
• This regulatory mechanism is distinct from that of group I capsules.
• A subset of E. coli strains may represent a novel group of capsular polysaccharides (tentatively group I/II) with distinct regulatory pathways.