Scientists Explore Secrets of the Anthrax Spore
Study May Help With Detection, Prevention and Early Treatment of Anthrax
December 16, 2003
In a pioneering joint use of genomics and proteomics to analyze a bacterial pathogen, scientists have described the molecular mechanisms behind the anthrax bacterium's ability to form tough spores that can survive for decades under harsh conditions yet still germinate quickly to infect an animal or human host.
That study of Bacillus anthracis spore formation - published in the January 1, 2004, issue of The Journal of Bacteriology, and posted on the journal's website on December 16 - provides information that other researchers can use in the development of new vaccines and treatments targeted at specific points in the process of anthrax growth and spore formation. The data may also be useful in the development of new technologies to detect and to decontaminate anthrax.
The report presents the first published results of a collaborative research project being conducted by scientists at three major research institutions - the University of Michigan, The Institute for Genomic Research (TIGR), and The Scripps Research Institute - with funding from the U.S. Office of Naval Research and the National Institutes of Health. The researchers are working together to identify the genes and proteins involved in the deadly metamorphosis of B. anthracis.
The new study is a pioneering analysis of a bacterial pathogen using the combined investigative tools of genomics and proteomics. It is also the first study to document, at a molecular level, the full range of genes and proteins involved in B. anthracis spore formation. Researchers identified 750 different proteins in the mature anthrax spore and found that a large number of genes are expressed in five discrete phases over a five-hour period during which the B. anthracis bacterium morphs from its normal state into spore form.
The study sheds light on the complex processes by which a microbe can sense the environmental factors (such as extreme dryness, cold or lack of nutrients) that require it to convert to spore form to survive, as well as the contrasting environmental conditions (such as the presence of water and nutrients) that signal the almost-dormant spore to regenerate into a normally-functioning bacterium.
"The most surprising result of this study is the degree of dedication this organism devotes to making its spore," says Philip C. Hanna, Ph.D., an assistant professor of microbiology and immunology at the University of Michigan Medical School, and the paper's corresponding author. "This shows how important the spore is to this organism's life cycle. The spore allows the anthrax bacterium to survive conditions that would kill most other living things."
TIGR scientists used DNA microarray technology to monitor gene expression changes in B. anthracis over time, as the bacteria made the transition from growth to the formation of spores. "Using cutting-edge techniques of functional genomics, we were able to shed new light on the molecular biology of the anthrax spore," says Scott N. Peterson, Ph.D., who led TIGR's role in the project.
Meanwhile, scientists at The Scripps Research Institute, in La Jolla, CA, used advanced proteomics analysis technologies to identify proteins expressed in anthrax spores. "Proteomics experiments can reveal the expression and localization of proteins in microorganisms," says John R. Yates, Ph.D., a cell biology professor at Scripps Research. "This is important, because some of these proteins may be promising targets for future vaccine development."
Hongbin Liu, Ph.D., a former Scripps Research post-doctoral research fellow and the paper's first author, adds that the study "clearly demonstrates the benefits of combining genomics and proteomics in a single study. The combined approach helped deepen our understanding of the complexity of spore growth and sporulation."
Microbiologists at the University of Michigan Medical School, in Ann Arbor, were responsible for working with the bacteria to study how it infects and causes disease in its human host. They also helped analyzed the large amounts of data generated by the study.
"Until recently, we knew how the anthrax spore was made on a microscopic level. We could see different structures forming, but we didn't know precisely what went into making them," says Nicholas H. Bergman, Ph.D., a research investigator in the U-M bioinformatics program and a coauthor of the paper. "Now we have a much clearer view of how the spore is assembled, and exactly what it is made of."
The collaboration's scientists identified 2,090 B. anthracis genes (of the nearly 6,000 genes in the entire genome) that appear to be expressed differently during the process of spore formation. Gene activity occurred in five overlapping waves spread across a five-hour period, but actual construction of the spore did not begin until the fourth wave of gene expression.
The ability of B. anthracis to form tough spores - in combination with the bug's virulence - made the anthrax bacterium a prime candidate for development as a biological weapon. Scientists have studied its spore form since pioneering German bacteriologist Robert Koch first described B. anthracis spore formation in 1876, but until recently researchers knew relatively little about the process in which a bacillus transforms itself into a dormant, metabolically inactive spore that can survive harsh conditions such as drought or deep freezes for decades.
"Because the spore is the infectious particle of the anthrax bacterium, it made sense to focus our technologies on exploring its molecular biology," says TIGR's Peterson.