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SUMMARY: Some strains of Chromobacterium exhibit either polar or mixed polar and peritrichous flagellation according to the conditions of culture. Polar and lateral flagella differ in the site of insertion, the wavelength, ease of staining, and in antigenic composition. Peritrichous flagellation is greatest in young cultures on solid media and is least in liquid media. The peritrichate flagella disappear in old agar plate cultures, leaving polar flagellated organisms. The arrangement of flagella has an important place in modern systems of bacterial classification. A species is usually considered to have either polar or peritrichate flagella but not both, and this feature is one of the main distinc- tions between, for instance, the pseudomonads and the enterobacteria. It was noticed that one strain of Chromobacterium appeared to possess two types of flagellum-a polar flagellum and a lateral flagellum of shorter wavelength. This was misinterpreted (Sneath, Whelan, Singh & Edwards, 1953) until the same appearance was found in the majority of strains of Chromobacterium (sensu stricto-i.e. the ' Bacterium violaceum ' group). Published descriptions of flagellation in the genus vary considerably, and it is clear that this appear- ance has been observed before, but without attracting comment. Thus Cruess- Callaghan & Gorman (1933) published photographs similar to P1.1, fig. 2, but attributed the variation to species differences; this has not been confirmed (Sneath, 1956). Lehmann & Neumann (1899,1, P1.23, figs. XI, XII; 2, p.180) showed drawings of predominantly peritrichate and predominantly polar strains, and commented that some strains showed both forms. Bampton (1913) somewhat ambiguously reported ' Geisseln 3-4 peritrich, 1-2 polar '. Most other authors report a single polar flagellum. Leifson & Hugh (1953) described certain strains of Aeromonas and Vibrio spp. which may show either peritrichate or polar flagella. In Aeromonas sp. the organisms in early phases of growth showed peritrichate flagella, and in old cultures only polar flagella. METHODS Strains. The strains are those described previously (Sneath, 1956), all belong- ing to the 'Bacterium violaceum' group. Flagella staining. The organisms were stained by the method of Leifson (1951). Cultures on solid media were suspended in distilled water, care being taken to avoid the picking up of fragments of medium. Liquid cultures were washed three times by centrifugation with distilled water before staining. Media. Nutrient broth was that of Hartley (1922), and nutrient agar was made by adding to it 1.5% (w/v) Japanese agar. Blood agar was nutrient

The Change from Polar to Peritrichous Flagellation in Chromobacterium spp.