Chemotaxis in Borrelia burgdorferi

Abstract

Borrelia burgdorferi is a motile spirochete which has been identified as the causative microorganism in Lyme disease. The physiological functions which govern the motility of this organism have not been elucidated. In this study, we found that motility of B. burgdorferi required an environment similar to interstitial fluid (e.g., pH 7.6 and 0.15 M NaCl). Several methods were used to detect and measure chemotaxis of B. burgdorferi. A number of chemical compounds and mixtures were surveyed for the ability to induce positive and negative chemotaxis of B. burgdorferi. Rabbit serum was found to be an attractant for B. burgdorferi, while ethanol and butanol were found to be repellents. Unlike some free-living spirochetes (e.g., Spirochaeta aurantia), B. burgdorferi did not exhibit any observable chemotaxis to common sugars or amino acids. A method was developed to produce spirochete cells with a self-entangled end. These cells enabled us to study the rotation of a single flagellar bundle in response to chemoattractants or repellents. The study shows that the frequency and duration for pausing of flagella are important for chemotaxis of B. burgdorferi.

FIG. 1

Cellular behavioral change in response to a chemoattractant (1% young rabbit serum; a) and a chemorepellent (100 mM ethanol; b). Wild-type B31 cells were used; the testing chemical was added to bacterial suspension at s 120, as indicated by an arrowhead. The behavioral change in response to the chemicals was studied by videomicroscopy, recorded by a VCR, and analyzed frame by frame for the ratio of time spent swimming and pausing-flexing (t_sw/t_p&f). Each data point represents a time ratio in a 30-s window. Data shown represent the behavioral change of one representative cell; more than 20 cells were studied, and similar results were observed.

FIG. 2

Cellular aggregation and self-entanglement of B. burgdorferi. (a) Wild-type B31 cells were grown in BSK II medium and resuspended at high cell density (OD₆₀₅ = 0.1) in solution containing 10 mM NaH₂PO₄ (pH 9.0), 10⁻⁴ M EDTA, 0.15 M NaCl, and 10 mg of BSA per ml. The arrowhead indicates a large cell clump. (b) Wild-type B31 cells were resuspended at low cell density (OD₆₀₅ = 0.005) in the buffer described above. The arrowhead indicates a cell with a self-entangled end.

FIG. 3

Gyration of the nontangled cell end in response to a chemoattractant (1% young rabbit serum; a) and a chemorepellent (100 mM ethanol; b). Low-density bacteria were suspended in solution containing 10 mM NaH₂PO₄ (pH 9.0), 0.15 M NaCl, 10⁻⁴ M EDTA, and 10 mg of BSA per ml. After production of cells with a self-entangled end, the bacteria were resuspended in the same buffer at pH 7.6 and mixed with testing chemicals at s 60, as indicated by an arrowhead. The gyration of the nontangled end was studied by videomicroscopy, recorded by a VCR, and analyzed frame by frame for the time spent on pushing (indicating CW rotation), pulling (indicating CCW rotation), and pausing (indicating no rotation). Data shown represents the behavioral change of one representative cell; more than 20 cells were studied, and similar results were observed.