13

Animations
(Animation Requirements)

• Lytic and Lysogenic Cycles in Prokaryotes
• The Life Cycle of HIV

Art Labeling Activities

• Nonphotosynthetic Bacterium
• Cyanobacterium

Infectious Disease and Bioterrorism
The new century has seen a new and potentially deadly way for disease to spread — by the deliberate actions of terrorists. After a brief discussion of infectious disease, this enhancement chapter reviews how microbes have been "weaponized" in bio-warfare programs, and takes a close look at anthrax and smallpox. It concludes by examining the future threat of gene-modified human and crop-plant pathogens.

Infectious Disease. One of the biggest impacts of biology on the human condition has been its contribution to the understanding and treatment of infectious disease. Smallpox, one of the great killers of history, remains a potential threat as a bioweapon. Other diseases stalk all of us. Even a Kentucky thoroughbred foal is not immune.

1. Smallpox: Tomorrow's nightmare?
2. Asking the hard questions about smallpox.
3. The silent epidemic of hepatitis C.
4. Using viruses to combat the rise in antibiotic-resistant pathogens.
5. Foot-and-mouth disease is more about money than health.
6. Science as detective work: The case of the dying racehorse foals.

The Threat of Bioweapons
One of the unfortunate nightmares of modern biotechnology is that it makes feasible the production of biological weapons of mass destruction. While plague and most other disease-causing bacteria and viruses are impractical as weapons, two killers are easy to produce, easy to dispense, and deadly: smallpox and anthrax. Anthrax is a deadly disease of cattle caused by a bacterium that forms endospores, making anthrax ideal for aerosol dispersal. Peak mortality for humans that breathe in the anthrax endospores is 89%. The peak mortality of smallpox is 30%, but smallpox can be expected to kill far more people than anthrax, because the virus which causes smallpox is easily transmissible. Infected people will make many others sick before they even know they are infected, causing the disease to spread like a chain reaction. Bioweapons were developed by the former Soviet Union, and there is concern that, with the breakdown of the Russian scientific establishment, strains of weaponized smallpox may reach terrorist nations. It is very important that the American public become informed of this danger, so that steps can be taken to prepare for disaster, should it strike.

How Pseudomonas "Sugar-Coats" Itself to Cause Chronic Lung Infections
The bacterium Pseudomonas aeruginosa infects the respiratory tract of cystic fibrosis patients, and is also found outside of the human body. Bacterial colonies of P. aeruginosa associated with cystic fibrosis exhibit a mucoid phenotype caused by the overproduction of a protein called alginate which forms an exopolysaccharide coat around each bacterial cell. This mucoid colony morphology, however, is rarely found in environmental isolates. Several gene mutations convert P. aeruginosa to the mucoid phenotype, all located within the so-called algUmucABCD gene cluster. What do these genes do? The mucA, mucB, and mucD genes each appear to have a negative regulatory role, keeping the cell in the nonmucoid phenotype. Very little is known about the function of mucC. Donald Rowen, now at the University of Nebraska, Omaha, has been studying the function of the enigmatic mucC gene. Some bacterial mutations are "conditional" — their effect on bacterial cells depends on their environment. His studies suggest that mucC is such a conditional mutation, acting — but only under adverse growth conditions — to inhibit growth.