A cryptic fimbrial gene in Serratia marcescens

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Serratia marcescens US5 possesses mannose-sensitive hemagglutinating fimbriae.
• Understanding fimbrial gene expression and function is crucial in bacterial pathogenesis.

Purpose of the Study:

• To clone and characterize the gene responsible for mannose-sensitive hemagglutinating fimbriae from S. marcescens US5.
• To investigate the expression of S. marcescens fimbrial genes in a heterologous host, Escherichia coli K4.

Main Methods:

• Cloning of S. marcescens US5 fimbrial genes into E. coli K4 using a cosmid vector.
• Morphological characterization of fimbriae using electron microscopy.
• Genetic analysis to determine gene location and subunit molecular weights via SDS-PAGE.
• Serological analysis using monoclonal and polyclonal antibodies.

Main Results:

• A transformant (US5-1) expressed two distinct fimbriae: 3-nm (identical to US5) and 5-nm wide.
• The genes for the 3-nm and 5-nm fimbriae were located over 10 kilobases apart.
• The 5-nm fimbriae subunits (20 kDa) differed from the 3-nm fimbriae subunits (19 kDa) and were serologically distinct.
• The 5-nm fimbriae did not agglutinate erythrocytes, suggesting a cryptic or non-functional role in the original strain.

Conclusions:

• The gene for the 5-nm-wide fimbriae is likely cryptic in S. marcescens US5.
• Heterologous expression in E. coli K4 facilitated the characterization of this previously unexpressed fimbrial gene.
• Transformation can reveal cryptic genes and enable functional studies of bacterial surface structures.