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four. One came from a flask labelled RMR-1029 that Ivins was responsible for at USAMRIID. The other seven came from cultures taken from that flask, only one of which was not located at USAMRIID. So while these findings show the attack spores came from one of these cultures, the FBI has gone further in concluding the attack came directly from the RMR-1029 flask. Another question is how the attacker turned the water-based slurry of spores in the flask to the fine, dry powder in the letters. Joseph Michael of the Sandia National Lab in Albuquerque, New Mexico, used specialised electron microscopy to show that 75 per –The chief suspect committed suicide last year– cent of the attack spores had incorporated silicon into their coats while growing (see image, been found were misleading. The below). As spores taken directly full genome sequences revealed “no genetic differences at all”, says from RMR-1029 following the Keim. Instead, the researchers say, attacks had no silicon in their coats, and the other seven genetic the key clues came from a lucky matches had either none or a discovery. A technician, also at USAMRIID, had noticed patches “The researchers say their the anthrax bacterium used in of unusual-looking spores in investigations only nail the attack as the US army’s Ames cultures of the attack anthrax, the source of the anthrax strain. The FBI then obtained 1072 and recultured just those. Keim and colleagues sequenced their spores, not the attacker” anthrax samples from the 18 labs genomes and found 10 mutations it knew to have Ames and got several research groups, including that differed from the common lower percentage, the attack Keim’s, to compare their genomes Ames sequence. Because the spores must have been recultured before they were posted. spores made up a fraction of the with that of the strain used in the During this process, they would total, these “minority” mutations attacks. The hope was this would have shed their coats, multiplied, hadn’t shown up initially. uncover mutations that would then turned back into spores. Was Next the team developed finger one lab as the source. Ivins’s level of expertise needed to But Keim and his colleagues told highly sensitive tests to screen turn these recultured spores into the Baltimore meeting that initial all 1072 samples for four of the dry powder? “What I am hearing reports that useful mutations had mutations. Eight samples had all is that the spores in the letter were not special. It would not take a lot Spore clues of time or equipment to make Electron microscopy of the anthrax sent to media outlets and politicians in 2001 provided vital clues to how the them,” says Keim. Michael’s spores were prepared images show the attack anthrax The attack samples contained clumps of Silicon incorporated into the coats of the contained spore clumps, unlike spores, suggesting they had not been attack spores shows that they were professionally produced powders. professionally produced recultured before being posted The FBI may have evidence to show Ivins was the link between RMR-1029 and the envelopes, though with civil suits from Ivins’ and the victims’ families pending, the bureau won’t be revealing it soon. For now, the researchers say their studies nail the spores as coming from the flask, but not 5 μm 1 μm the identity of the attacker. ■
Debora MacKenzie
KEY forensic evidence in the US anthrax attacks of 2001 has been revealed. The FBI had previously prevented the scientists involved from speaking publicly about their findings in case this interfered with court proceedings, but last August, after chief suspect Bruce Ivins committed suicide, the case collapsed and the FBI lifted many of the restrictions. This week, some of the scientists involved revealed their results at a scientific meeting in Baltimore, Maryland. These show how the FBI traced the spores used in the attacks to a single flask at a US government lab, but they don’t explain why the FBI made Ivins – who worked at the US Army Medical Research Institute for Infectious Diseases (USAMRIID) – the chief suspect. In late 2001, envelopes containing dry anthrax spores were sent to a number of US media outlets and politicians, leading to five deaths. Later that year, Paul Keim at the Northern University of Arizona in Flagstaff identified
SOURCE: SANDIA NATIONAL LABORATORY
Behind the 2001 anthrax attacks
28 February 2009 | NewScientist | 13