Morphological, serological and chemical studies on bacterial flagella with particular reference to Escherichia coli and Salmonella

Mutants were isolated, mostly from strains of Salmonella, which possessed aberrant motility due to defects in the construction of the flagellar filament.These mutants were characterised by electron microscopy and the helical shape of the filament shown to exhibit abnormalities of pitch or amplitude, or both pitch and amplitude. Normally motile and partially motile revertants of non-motile mutants ("straight" or "curly" filaments) were also isolated and characterised. Recovery of motility was either due to full reversion to the normal waveform, possession of extra long but curly filaments, or possession of short filaments presumably of the normal waveform. In the latter two cases swarming through soft agar was slow. The variation in filament surface structure amongst strains of Escherichia coli (morphotypes) reported by Lawn, Orskov and Orskov (1977) was confirmed but no similar variations were found amongst a wide range of bacterial genera investigated. Attempts to "convert" one surface type of Escherichia coli to another by selection in media containing appropriate antisera were unsuccessful though mutants with considerably less specificity for the original antiserum were obtained. No serological cross-reactions were detected between flagella of Salmonella and those of Escherichia coli. Chemical studies were initiated on flagellins from different filament morphotypes of Escherichia coli. These investigations involved comparisons of molecular size, amino acid composition and amino acid sequence, the latter deduced from peptide maps, fragments obtained by cleavage with cyanogen bromide and treatment of flagellins and fragments with carboxypeptidases. One cyanogen bromide fragment appeared to be common to all the Escherichia coli flagellins studied and is thought to represent a conserved region.