SYMPOSIA PAPER Published: 01 January 1989

Laser/Microbe Bioassay System


The laser/microbe bioassay was developed to meet the needs of the Department of Defense and National Institutes of Environmental Health Sciences for a rapid detection system to detect low quantities of toxic contaminants in potable water (that is, the U.S. EPA's priority pollutants). The bioassay system consists of the Dawn B Laser Photometer, which makes 1200 measurements/s at 15 unique angles, and an isogenic set of Bacillus subtilis mutants. Toxicity to the bacteria is detected by differential light scattering (DLS) of the laser beam, which measures the response of the bacteria in terms of light intensity at various angles over 180°. The DLS pattern (liquid sample) shows the number of particles present, their size, shape, and the distribution of particles [that is, if a bacterial culture increases in numbers, there will be an overall increase or decrease in intensity (number of particles)]. If the bacteria increase or decrease in size, the intensity versus angles (DLS pattern) will shift. Therefore, shrinking, swelling, or failure of the bacteria to divide over time are the measured parameters of toxicity. Concentration of the toxicant is determined by the level of response by the bacteria in a given sample.

The 19 bacteria each differ by only one property, which causes them to be more sensitive than other set members based on the mechanism of toxicity. Therefore, a fingerprint or profile unique to each chemical is generated from the differential response of the member bacteria (for example, a profile unique for malathion, dibrom, lindane, 2,4,5, trichJorophenol, and chromate has been generated using this system). In addition, this system has been used to detect malathion extracted from oil base cards used in monitoring fields sprayed with malathion.

The time required for a complete assay is approximately 66 min (time required for untreated bacteria to divide twice in the absence of any toxicant). However, individual samples can be read and analyzed by the computerized system at a rate of one sample/min (that is, 5 to 10 concentrations of an aqueous sample are easily processed in just over an hour), generating data for: (1) identifying test material; (2) assessing concentration of test material; and (3) assessing whether test material is acutely or chronically toxic.

Author Information

Felkner, IC
Technical Assessment Systems, Inc., Washington, DC
Worthy, B
Technical Assessment Systems, Inc., Washington, DC
Christison, T
Technical Assessment Systems, Inc., Washington, DC
Chaisson, C
Technical Assessment Systems, Inc., Washington, DC
Kurtz, J
U.S. Environmental Protection Agency, Washington, DC
Wyatt, PJ
Wyatt Technology Corp., Santa Barbara, CA
Price: $25.00
Contact Sales
Reprints and Permissions
Reprints and copyright permissions can be requested through the
Copyright Clearance Center
Developed by Committee: E47
Pages: 95–103
DOI: 10.1520/STP16774S
ISBN-EB: 978-0-8031-5088-1
ISBN-13: 978-0-8031-1253-7