Microbiology and Immunology

Fossilization of bacteria WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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animals were decimated, and tourists avoided the English

countryside. Use of an available vaccineto attempt to curb the

epidemic was rejected by most scientists, as the virus incuba-

tion time was short (often less than 72 hours), and the immu-

nitygained from the vaccine was short-lived. Meanwhile, the

Unites States and other countries adopted inclusive measures

to prevent the importation of the foot-and-mouth virus, from

carefully restricting the importation of animal products, to the

sanitizing of shoes of airplane passengers arriving in the U.S.

from England. As of April 2002, the outbreak continued to be

contained, with the last confirmed foot-and-mouth case in

England occurring six months prior at a farm in

Northumberland, and the restoration of “Foot-and-mouth-

Free” status restored to livestock herds of the United Kingdom

by the World Organization for Animal Health (Office

Internationale des Epizooties).

See alsoAnimal models of infection; Epidemics, viral;

Epidemiology, tracking diseases with technology;

Epidemiology; Veterinary microbiology

FORENSIC IDENTIFICATION OF MICRO-

ORGANISMS•seeGENETIC IDENTIFICATION OF MICRO-

ORGANISMS

FORENSIC IMMUNOLOGY AND BACTERI-

OLOGY•seeGENETIC IDENTIFICATION OF MICRO-

ORGANISMS

FFossilization of bacteriaOSSILIZATION OF BACTERIA

Studies of fossilization of bacteriaprovide an indication of the

age of ancient bacteria. Fossils of cyanobacteria or “blue-

green algae” have been recovered from rocks that are nearly

3.5 million years old. Bacteria known as magnetobacteria

form very small crystals of a magnetic compound inside the

cells. These crystals have been found inside rock that is two

billion years old.

The fossilization process in cyanobacteria and other

bacteria appears to depend on the ability of the bacteria to trap

sediment and metals from the surrounding solution.

Cyanobacteria tend to grow as mats in their aquatic environ-

ment. The mats can retain sediment. Over time and under pres-

sure the sediment entraps the bacteria in rock. As with other

living organisms, the internal structure of such bacteria is

replaced by minerals, notably pyrite or siderite (iron carbon-

ate). The result, after thousands to millions of years, is a

replica of the once-living cell.

Other bacteria that elaborate a carbohydrate network

around themselves also can become fossilized. The evidence

for this type of fossilization rests with laboratory experiments

where bacteria are incubated in a metal-containing solution

under conditions of temperature and pressure that attempt to

mimic the forces found in geological formations. Experiments

with Bacillus subtilisdemonstrated that the bacteria act as a

site of precipitation for silica, the ferric form of iron, and of

elemental gold. The binding of some of the metal ions to

available sites within the carbohydrate network then acts to

drive the precipitation of unstable metals out of solution and

onto the previously deposited metal. The resulting cascade of

precipitation can encase the entire bacterium in metallic

species. On primordial Earth, this metal binding may have

been the beginning of the fossilization process.

The deposition of metals inside carbohydrate networks

like the capsule or exopolysaccharide surrounding bacteria is a

normal feature of bacterial growth. Indeed, metal deposition can

change the three-dimensional arrangement of the carbohydrate

strands so as to make the penetration of antibacterial agents

through the matrix more difficult. In an environment—such as

occurs in the lungs of a cystic fibrosis patient— this micro-fos-

silization of bacteria confers a survival advantage to the cells.

In contrast to fossils of organisms such as dinosaurs, the

preservation of internal detail of microorganisms seldom

occurs. Prokaryotes have little internal structure to preserve.

However, the mere presence of the microfossils is valuable, as

they can indicate the presence of microbial life at that point in

geological time.

Bacteria have been fossilized in amber, which is fos-

silized tree resin. Several reports have described the resuscita-

tion of bacteria recovered from amber as well as bacteria

recovered from a crystal in rock that is millions of years old.

Although these claims have been disputed, a number of micro-

biologists assert that the care exercised by the experimenters

lends increases the validity of their studies.

In the late 1990s a meteorite from the planet Mars was

shown to contain bodies that appeared similar to bacterial fos-

sils that have been found in rocks on Earth. Since then, further

studies have indicated that the bodies may have arisen by inor-

ganic (non-living) processes. Nonetheless, the possibility that

these bodies are the first extraterrestrial bacterial fossils has

not been definitively ruled out.

See alsoBacterial surface layers; Biogeochemical cycles;

Glycocalyx

FFriend, Charlotte RIEND, CHARLOTTE(1921-1987)

American microbiologist

As the first scientist to discover a direct link between viruses

and cancer, Charlotte Friend made important breakthroughs in

cancer research, particularly that of leukemia. She was suc-

cessful in immunizing mice against leukemia and in pointing

a way toward new methods of treating the disease. Because of

Friend’s work, medical researchers developed a greater under-

standing of cancer and how it can be fought.

Friend was born on March 11, 1921, in New York City to

Russian immigrants. Her father died of endocarditis (heart

inflammation) when Charlotte was three, a factor that may have

influenced her early decision to enter the medical field; at age

ten she wrote a school composition entitled, “Why I Want to

Become a Bacteriologist.” Her mother’s job as a pharmacist

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