Analyzing small pieces of tissue from nearly 40-year-old human autopsies, Arizona researchers have sequenced the genome of the strain of Bacillus anthracis that caused a deadly anthrax outbreak in Russia in 1979. The work is published this week in mBio®, an online open-access journal of the American Society for Microbiology.
B. anthracis had been studied by multiple countries as a potential biological weapon because of the stability of its spores and its ability to cause acute pulmonary disease. Offensive anthrax weapons development programs were halted in the United States and United Kingdom in the 1960s but continued covertly in the former Soviet Union for at least another 20 years, said senior study author Paul Keim, professor and director of the Pathogen Genomics Program, a joint program of Northern Arizona University in Flagstaff and the Translational Genomics Research Institute in Phoenix. The Russian research included projects to genetically modify the organism to be antibiotic-resistant, said Keim, Regents professor of biology and the Cowden Endowed Chair in microbiology at the university.
In April 1979, safety air filters at a military facility that had been conducting B. anthracis studies in the city of Sverdlovsk were compromised during routine maintenance, resulting in bacterial cells spreading downwind of the facility. At least 66 people and some livestock died of inhalational anthrax.
In the current study, investigators determined that the strain of B. anthracis that caused this outbreak is most closely related to the Russian Tsiankovskii vaccine strain of the organism. Despite concern that the Soviets were manipulating the organism to become drug-resistant, the strain identified here was simply a natural strain most likely isolated for its biological properties, Keim said; there was no evidence that it had been manipulated in the lab or mixed with other strains. The genome has been made public through the National Center for Biotechnology Information Genome Database.
"This work provides insights into the world's largest biological weapons program and provides an extensive B. anthracis reference," Keim said. "We now know what the genome for this strain looks like, so if it ever occurs again, we will be able to pinpoint that this original came from the Soviet weapons program."
For the study, Keim and colleagues used deep sequencing technology to analyze B. anthracis DNA extracted from spleen and lymph node tissue taken from autopsies of two of the individuals who died in the 1979 Russian anthrax outbreak. To reconstruct the genome, they compared the genetic information from this strain against the Ames strain of B. anthracis, which is most commonly known for being mailed in letters to several news media offices and two U.S. senators in 2001, killing five people and infecting 17 others. Next, they compared the genomes of 193 strains of B. anthracis against the Ames strain and the new strain to look for variation. There were only 13 variants seen in the new genome versus its closest relative.
"Our findings indicate that the Soviet weapons program identified a suitable strain, maintained master cell stocks and performed minimal manipulations in order to maintain virulence," Keim said. "This strategy must have been used to produce large quantities of highly virulent material, as evidenced by the anthrax deaths in 1979."
The study was supported by the Department of Homeland Security Science and Technology Directorate.