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Abstract
Rhizobium meliloti MVII-1 and Rhizobium lupini H13–3, two strains with five to ten peritrichously inserted complex flagella, were studied with respect to motility and chemotaxis. Cells of both these strains move rapidly with speeds up to 40 μm s−1 (R. meliloti) and 60 μm s−1 (R. lupini) respectively. Increasing viscosity causes little reduction in their swimming velocities as compared with Salmonella typhimurium propelled by plain flagella. It is suggested that complex flagella possess a high ‘flexural rigidity’, which serves to maintain a helix conformation favourable for propulsive efficiency at increased viscosities. Chemotaxis in R. meliloti MVII-1 and R. lupini H13–3 was studied and the conditions required have been defined using the capillary tube assay. All 20 common l-amino acids and l-homoserine were shown to be attractive to R. meliloti MVII-1 with thresholds varying from 10−6 m (proline) to 10−4 m (aspartate). Leucine, proline and lysine elicited optimal responses. Rhizobium lupini H13–3 was also attracted by l-amino acids except for leucine, which elicited no response. Aspartate was a significantly better attractant of R. lupini H13–3 than of R. meliloti MVII-1, and glycine, isoleucine, homoserine, serine, threonine, cysteine, glutamine and glutamate were poorer attractants. Chemotaxis towards various carbohydrates was generally better in R. lupini H13–3 than in R. meliloti MVII-1. It is concluded that bacteria with complex flagella are efficient swimmers in viscous environments and are capable of responding to chemotactic stimuli.
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