Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Gas vacuoles and gas vesicles

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Human Services, and in December of that year, ORI found

both Gallo and Popovic guilty of scientific misconduct.

Based largely on a single sentence in the 1984 Sciencearticle

that described the isolation of the virus, the ORI report found

Gallo guilty of misconduct for “falsely reporting that LAV

had not been transmitted to a permanently growing cell line.”

This decision renewed the legal threat from the Pasteur

Institute, whose lawyers moved to claim all the back royalties

from the AIDS blood test, which then amounted to approxi-

mately $20 million.

Gallo strongly objected to the findings of the ORI,

pointing to the fact that the finding of misconduct turned on a

single sentence in a single paper. Other scientists objected to

the panel’s priorities, arguing that the charge of misconduct

concerned a misrepresentation of a relatively minor issue

which did not negate the scientific validity of Gallo’s conclu-

sions. Lawyers representing both Gallo and Popovic brought

their cases before an appeals board at the Department of

Health and Human Services. Popovic’s case was heard first,

and in December 1993, the board announced that he had been

cleared of all charges. As quoted in Time,the panel declared:

“One might anticipate... after all the sound and fury, there

would be at least a residue of palpable wrongdoing. This is not

the case.” The ORI immediately withdrew all charges against

Gallo for lack of proof.

According to Time,in December 1993, Gallo consid-

ered himself “completely vindicated” of all the allegations that

had been made against him. He has established that before

1984 his laboratory had succeeded in isolating other strains of

the virus that were not similar to LAV. Many scientists now

argue that the problem was simply one of contamination, a

mistake which may have been a consequence of the intense

pressure for results in many laboratories during the early years

of the AIDS epidemic. It has been hypothesized that the LAV

sample from the Pasteur Institute contaminated the mixture of

AIDS viruses that Popovic concocted to find one strain that

would survive in culture; it is believed that this strain was

strong enough to survive and be identified by Gallo and

Popovic for a second time.

In 1990, when the controversy was still at its height,

Gallo published a book about his career called Virus Hunting,

which seemed intended to refute the charges against him, par-

ticularly the Tribunearticle by Crewdson. Gallo made many of

the claims that were later supported by the appeals board, and

in the New York Times Book Review,Natalie Angier called him

“a formidable gladiator who firmly believes in the importance

of his scientific contributions.” Angier wrote of the book: “His

description of the key experiments in 1983 and 1984 that led

to the final isolation of the AIDS virus are intelligent and per-

suasive, particularly to a reader who was heard the other side

of the story.”

The many allegations and the long series of investiga-

tions have distracted many people from the accomplishments

of a man whose name appears on hundreds of scientific papers

and who has won most major awards in biomedical research

except the Nobel Prize. Gallo received the coveted Albert

Lasker Award twice, once in 1982 for his work on the viral ori-

gins of cancer, and again in 1986 for his research on AIDS. He

has also been awarded the American Cancer Society Medal of

Honor in 1983, the Lucy Wortham Prize from the Society for

Surgical Oncology in 1984, the Armand Hammer Cancer

Research Award in 1985, and the Gairdner Foundation

International Award for Biomedical Research in 1987. He has

received eleven honorary degrees.

See alsoAIDS, recent advances in research and treatment;

Antibody and antigen; Antibody formation and kinetics;

Antibody-antigen, biochemical and molecular reactions;

Viruses and responses to viral infection

GGas vacuoles and gas vesiclesAS VACUOLES AND GAS VESICLES

Gas vacuoles are aggregates of hollow cylindrical structures

called gas vesicles. They are located inside some bacteria. A

membrane that is permeable to gas bound each gas vesicle.

The inflation and deflation of the vesicles provides buoyancy,

allowing the bacterium to float at a desired depth in the water.

Bacteria that are known as cyanobacteria contain gas

vacuoles. Cyanobacteria, which used to be called blue-green

algae, live in water and manufacture their own food from the

photosynthetic energy of sunlight. Studies have demonstrated

that the inflation and deflation of the gas vesicles is coordi-

nated with the light. The buoyancy provided by the gas vac-

uoles enables the bacteria to float near the surface during the

day to take advantage of the presence of sunlight for the man-

ufacture of food, and to sink deeper at night to harvest nutri-

ents that have sunk down into the water.

Gas vesicles are also found in some archae, bacteria that

are thought to have branched off from a common ancestor of

eukaryotesand prokaryotes at a very early stage in evolution.

For example, the gas vesicles in the bacterium Halobacterium

NRC-1allow the bacteria to float in their extremely salt water

environments (the bacteria are described as halophilic, or “salt

loving.” The detailed genetic analysis that has been done with

this bacterium indicates that at least 13 to 14 genes are

involved in production of the two gas vesicle structural pro-

teins and other, perhaps regulatory, proteins. For example,

some proteins may sense the environment and act to trigger

synthesis of the vesicles. Vesicle synthesis is known to be trig-

gered by low oxygen concentrations.

The gas vesicles tend to be approximately 75 nanome-

ters in diameter. Their length is variable, ranging from 200 to

1000 nanometers, depending on the species of bacteria. The

vesicles are constructed of a single small protein. In at least

some vesicles these proteins are linked together by another

protein. The interior of the protein shell is very hydrophobic

(water-hating), so that water is excluded from the inside of the

vesicles. Yet it is still unclear how the regular arrangement of

proteins produces a shell that is permeable to gas. Presumably

there must be enough space in between the protein subunits to

permit the passage of air.

See alsoBlue-green algae; Photosynthetic microorganisms

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