Swimming characteristics of magnetic bacterium, Magnetospirillum sp AMB-1,and implications as toxicity measurement

To develop a novel toxicity measurement system using the persistent swimmin g property of magnetic bacteria along an externally applied magnetic field, certain characteristics of Magnetospirillum sp. AMB-1 cells were examined, including their growth pattern, motility, magnetosensitivity, swimming spe ed, and cell length distribution. In addition, the effect of toxic compound s on the swimming speed was assessed relative to application as a toxicity sensor. With an inoculum of 1.0 x 10(8) cells/mL, the cells reached the sta tionary phase with a concentration of about 5 x 10(8) cells/mL after 20 h, under both aerobic and anaerobic conditions. The distribution of the cell l ength did not vary significantly during the growth period, and both aerobic ally and anaerobically growing cells showed a similar cell length distribut ion. Although the cells showed similar growth patterns under both condition s, the anaerobically grown cells exhibited higher motility and magnetosensi tivity. Actively growing cells under anaerobic conditions had an average sw imming speed of 49 mum/s with a standard deviation of 20 mum/s. When the an aerobically growing cells were exposed to various concentrations of toxic c ompounds, such as l-propanol and acetone, the swimming speed decreased with an increased concentration of the toxic compound. Accordingly, the relatio nship between swimming speed and toxicity can be used as an effective quant itative toxicity measurement; furthermore, the relative sensitivity of the proposed system was comparable to Microtox, which is commercially available . (C) 2001 John Wiley & Sons, Inc.