It took less than a teaspoonful of a strange powder, delivered in sealed, crudely addressed envelopes, to kill five Americans and critically infect eight others. The devil in those details, on the East Coast late in 2001, had all the earmarks of anthrax - Bacillus anthracis.

On Jan. 22, the U.S. government began deploying environmental monitors to detect airborne bioterrorism agents, notably anthrax and smallpox. The system relies on filtering air and sending the filters to a lab, where any attached microbes would be cultured and identified. Even with advanced techniques such as PCR (polymerase chain reaction) to detect microbial genes, the turnaround time would be 12 to 24 hours.

"If we are able to discriminate between bacterial spores, based on their size or swelling characteristics, it's a monitoring test we could do in seconds to minutes," observed Andrew Westphal, a research physicist at the Space Sciences Laboratory at the University of California at Berkeley.

Westphal is first author of a paper released online Feb. 25, 2003, by the Proceedings of the National Academy of Sciences (PNAS). Its title: "Kinetics of size changes of individual Bacillus thuringiensis [Bt] spores in response to changes in relative humidity."

(How did Bt - the farmer's crop-protective insecticidal friend - get into the anthrax bacillus act? Of 13 alphabetically listed Bacillus species, the first and last - B. thuringiensis and B. anthracis - are the most closely related in their molecular structure. So anthrax researchers pinch-hit for the deadly organism by going to Bt as their bacterial whipping-bug.)

"In the overall finding of this PNAS article," Westphal told BioWorld Today, "we have applied to a biological problem tools that we use in astrophysics research. And we discovered something that we think is somewhat new. It appears that bacterial spores respond quite rapidly to changes in the environment. With changes in the humidity, they actually change physically in size. That phenomenon is evidently quite a surprise to biologists."

From Outer Space To Inner Lurking Spores

"We came by this finding," Westphal continued, "because we became interested in the problem of identifying bacterial spores after the East Coast anthrax mail events. We already have an automated microscope that we use for analyzing nuclear track-etch detectors for many different space applications. Most notably, we had an array of detectors up on the Russian space station that we used for measuring the composition of galactic cosmic rays. We had developed this automated microscope many years ago for the analysis of these detectors, and it occurred to us that it would be interesting to try to distinguish between different types of bacterial spores, based on their size.

"So we started to investigate that, and did in fact find that, apparently, different types of bacterial endospores have physically different sizes. And one of the thoughts that occurred to us was that maybe humidity had some effect. So we introduced alterations in humidity in the microscope chamber, and discovered that the spore did in fact change in size. With diameters of around 2 microns - about one-hundredth the width of a human hair - they are smaller than the resolution limit of most optical microscopes.

"It's possible as a practical matter - one of the things we're interested in pursuing - that this observation could lead to a useful device that can distinguish between different spores, to provide a first line of detection - perhaps for anthrax. It may be," Westphal speculated, "that different types of spores swell with different time scales, with different amplitudes, and help to distinguish one bacterial type from another.

"Roughly, in the automated microscope," he went on," we measured many, many times, looking at the image of each individual spore. These looked like ellipses in the field of view. For a single measurement, which we're averaging, we measure each one about 110 times. Then in the course of a few hours we measure them thousands and thousands of times. By averaging over many measurements, we could achieve better than 5 nanometer's resolution in relative size. Now what we saw first was spores swelling about 2.9 percent in less than 50 seconds, then increased another 0.9 percent after about 8 minutes. We speculate that we were seeing, first, the uptake in the spore coat, which caused a relatively rapid and large change in size. That was followed by absorption into the spore's cortex.

"We speculate in the PNAS paper that changing humidity causes a swelling, which opens up pores. This allows the humidity change, the moist air, to enter the permeable pore more effectively. It's been a surprise to biologists that the long-dormant inert spore is not technically alive. It doesn't metabolize in spore phase, and can be stable for centuries with no metabolism. So they don't require nutrients. Humidity may be the first step for bringing them back to life. It may allow better access of these spores to the interior, not only to anti-anthrax toxins, such as chlorine dioxide, but also to nutrients."

At some future point, Westphal and his co-authors will turn to the design of a quick and cheap anthrax detection device. "Right now," he said, "we're looking at spores from different species - Bacillus subtilis, thuringiensis, cereus - a long, long laundry list. We also plan to move our equipment to a lab that has de-fanged Bacillus anthracis, and do a measurement list on that dangerous species as well."

Quick, Cheap Detector Kit On Back Burner

"At the moment, we haven't gone so far as thinking in much detail about a practical detection kit," he said. "But I think such a system would be as simple as a microscope with a computer-controlled stage and an imaging system. Not much more than that. Some way also to control the humidity in the chamber on a rapid time scale. It would definitely be a desktop piece of equipment - such as what we use right now. We've made no attempt to miniaturize it.

"Our next research step, now ongoing," Westphal went on, "is to verify and distinguish between different species, and measure their humidity uptake characteristics. That's going to be our focus for the next few months, and depending on what we find," he concluded, "we will go from there."