Microbiology and Immunology

Marshall, Barry J. WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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3300 feet (1000 meters) in depth. The pressure on objects like

bacteria at increasing depths is enormous.

Some marine bacteria have adapted to the pressure of the

ocean depths and require the presence of the extreme pressure

in order to function. Such bacteria are barophilic if their require-

ment for pressure is absolute or barotrophic if they can tolerate

both extreme and near-atmospheric pressures. Similarly, many

marine bacteria have adapted to the cold growth temperatures.

Those which tolerate the temperatures are described as psy-

chrotrophic, while those bacteria that require the cold tempera-

tures are psychrophilic (“cold loving”).

Marine waters are elevated in certain ions such as

sodium. Not surprisingly, marine microbes like bacteria have

an absolute requirement for sodium, as well as for potassium

and magnesium ions. The bacteria have also adapted to grow

on very low concentrations of nutrients. In the ocean, most of

the organic material is located within 300 meters of the sur-

face. Very small amounts of usable nutrients reach the deep

ocean. The bacteria that inhabit these depths are in fact inhib-

ited by high concentrations of organic material.

The bacterial communication system known as quorum

sensingwas first discovered in the marine bacterium Vibrio

fischeri. An inhibitor of the quorum sensing mechanism has

also been uncovered in a type of marine algae.

Marine microbiology has become the subject of much

commercial interest. Compounds with commercial potential

as nutritional additives and antimicrobials are being discov-

ered from marine bacteria, actinomycetes and fungi. For

example the burgeoning marine nutraceuticals market repre-

sents millions of dollars annually, and the industry is still in its

infancy. As relatively little is still known of the marine micro-

bial world, as compared to terrestrial microbiology, many

more commercial and medically relevant compounds

undoubtedly remain to be discovered.

See also Bacterial kingdoms; Bacterial movement;

Biodegradable substances; Biogeochemical cycles

MMarshall, Barry J.ARSHALL, BARRYJ.(1951- )

Australian physician

Barry Marshall was born in Perth, Australia. He is a physician

with a clinical and research interest in gastroenterology. He is

internationally recognized for his discovery that the bacterium

Helicobacter pyloriis the major cause of stomach ulcers.

Marshall studied medicine at the University of Western

Australia from 1969 to 1974. While studying for his medical

degree, Marshall decided to pursue medical research. He

undertook research in the laboratory of Dr. Robin Warren, who

had observations of a helical bacteriain the stomach of people

suffering from ulcers.

Marshall and Warren succeeded in culturing the bac-

terium, which they named Helicobacter pylori. Despite their

evidence that the organism was the cause of stomach ulcera-

tion, the medical community of the time was not convinced

that a bacterium could survive the harsh acidic conditions of

the stomach yet alone cause tissue damage in this environ-

ment. In order to illustrate the relevance of the bacterium to

the disease, Marshall performed an experiment that has earned

him international renown. In July of 1984, he swallowed a

solution of the bacterium, developed the infection, including

inflammationof the stomach, and cured himself of both the

infection and the stomach inflammation by antibiotic therapy.

By 1994, Marshall’s theory of Helicobacter involve-

ment in stomach ulcers was accepted, when the United States

National Institutes of Health endorsed antibioticss the stan-

dard treatment for stomach ulcers.

Since Marshall’s discovery, Helicobacter pylorihas

been shown to be the leading cause of stomach and intestinal

ulcers, gastritis and stomach cancer. Many thousands of ulcer

patients around the world have been successfully treated by

strategies designed to attack bacterial infection. Marshall’s

finding was one of the first indications that human disease

thought to be due to biochemical or genetic defects were in

fact due to bacterial infections.

From Australia, Marshall spent a decade at the

University of Virginia, where he founded and directed the

Center for Study of Diseases due to H. pylori. While at

Virginia, he developed an enzyme-based rapid test for the

presence of the bacterium that tests patient’s breath. The test is

commercially available.

Currently, he is a clinician and researcher at the Sir

Charles Gairdner Hospital in Perth, Australia.

Marshall’s discovery has been recognized internation-

ally. He has received the Warren Alpert Prize from the Harvard

Medical School, which recognizes work that has most bene-

fited clinical practice. Also, he has won the Paul EhrlichPrize

(Germany) and the Lasker Prize (United States).

See alsoBacteria and bacterial infection; Helicobacteriosis

MMastigophoraASTIGOPHORA

Mastigophora is a division of single-celled protozoans. There

are approximately 1,500 species of Mastigophora. Their habi-

tat includes fresh and marine waters. Most of these species are

capable of self-propelled movement through the motion of one

or several flagella. The possession of flagella is a hallmark of

the Mastigophora.

In addition to their flagella, some mastigophora are able

to extend their interior contents (that is known as cytoplasm)

outward in an arm-like protrusion. These protrusions, which

are called pseudopodia, are temporary structures that serve to

entrap and direct food into the microorganism. The cytoplas-

mic extensions are flexible and capable of collapsing back to

form the bulk of the wall that bounds the microorganism.

Mastigophora replicate typically by the internal dupli-

cation of their contents flowed by a splitting of the microbes

to form two daughter cells. This process, which is called

binary fission, is analogous to the division process in bacteria.

In addition to replicating by binary fission, some

mastigophora can reproduce sexually, by the combining of

genetic material from two mastigophora. This process is

referred to as syngamy.

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