'Viscotaxis', a new behavioural response of Leptospira interrogans (biflexa) strain B16.

When in a non-viscous environment and confronted with a viscous one, Leptospira interrogans (biflexa) strain B16 preferentially selected the latter. We have designated this positive response to a viscosity gradient as 'viscotaxis'. Using an originally designed experimental chamber, a pool of leptospires were faced with capillary tubes containing either polyvinylpyrrolidone (PVP) or N-2-hydroxyethylpiperazine-N'-2-ethanesulphonic acid (HEPES). Leptospires suspended in HEPES responded positively to 2% (w/v) PVP in capillaries, and migrated into them in large numbers in 1 h. No response was observed when the chamber and capillary tubes contained solutions of the same viscosity. As the viscosity of PVP was increased, a proportionally larger number of leptospires migrated into it. This newly observed aspect of leptospiral behaviour may have ecological significance.