Microbiology and Immunology

Colwell, Rita R. WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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faster, and often grow in the direction of the nutrient source.

Even the shape of the bacteria changes from an oval to a

longer form in these fast growing regions. The molecular basis

of this shape transformationremains unresolved.

In another example of the influence of the surface on

colony dynamics, the periphery of colonies grown on wet sur-

faces contains very motile (moveable) bacteria. Their motion

is constrained by the high number of bacteria. The results is

the formation of so-called “whirls and jets” that form, disap-

pear and re-form. These motions, which appear under the

light microscopeto be very random and chaotic, are in fact

very highly organized and helps drive the further formation of

the colony.

Another phenomenon of colony formation is the com-

munication between constituent cells. This is also known as

“cross-talk.” Cells of the amoeba Dictyostelium discoideum,

for example, can actually signal one another when growing

in a colony, especially in nutrient-poor environments. Cells

that encounter nutrients emit a compound called cyclic

adenosine monophosphate (cAMP). The subsequent growth

of cells is in the direction of the increasing cAMP concen-

tration. Visually, a spiraling pattern of growth results.

Mounds of amoebas also form. The microbes at the top of the

mounds produce spores that can become dispersed by air

movement, allowing the colonization and new colony forma-

tion of other surfaces.

Chemical signalling within a colony has also been

demonstrated in yeast, such as Candida mogiiand in bacteria,

such as Escherichia coli.

See alsoAgar and agarose; Biofilm formation and dynamic

behavior

CColwell, Rita R.OLWELL, RITAR.(1934- )

American marine microbiologist

Rita R. Colwell is a leader in marine biotechnology, the

application of molecular techniques to marine biology for

the harvesting of medical, industrial and aquaculture prod-

ucts from the sea. As a scientist and professor, Colwell has

investigated the ecology, physiology, and evolutionary rela-

tionships of marine bacteria. As a founder and president of

the University of Maryland Biotechnology Institute, she has

nurtured a vision to improve the environment and human

health by linking molecular biologyand genetics to basic

knowledge scientists have gleaned from life and chemistry in

the oceans.

Rita Rossi was born in Beverly, Massachusetts, the

seventh of eight children to parents Louis and Louise Di

Palma Rossi. Her father was an Italian immigrant who estab-

lished his own construction company, and her mother was an

artistic woman who worked to help ensure her children

would have a good education. She died when her daughter

was just thirteen years old, but she had expressed pride in her

success in school. In the sixth grade, after Rossi had scored

higher on an IQ test than anyone previously in her school,

the principal sternly stressed that Rossi had the responsibil-

ity to go to college. Eventually, Rossi received a full schol-

arship from Purdue University. She earned her B.S. degree

with distinction in bacteriology in 1956. Although she had

been accepted to medical school, Rossi chose instead to earn

a master’s degree so that she could remain at the same insti-

tution as graduate student Jack Colwell, whom she married

on May 31, 1956. Colwell would have continued her studies

in bacteriology, but the department chairman at Purdue

informed her that giving fellowship money to women would

have been a waste. She instead earned her master’s degree in

the department of genetics. The University of Washington,

Seattle, granted her a Ph.D. in 1961 for work on bacteria

commensal to marine animals, which is the practice of an

organism obtaining food or other benefits from another

without either harming or helping it. Colwell’s contributions

included establishing the basis for the systematics of marine

bacteria.

In 1964, Georgetown University hired Colwell as an

assistant professor, and gave her tenure in 1966. Colwell and

her research team were the first to recognize that the bac-

terium that caused cholera occurred naturally in estuaries.

They isolated the bacterium from Chesapeake Bay and in

ensuing years sought to explain how outbreaks in human

populations might be tied to the seasonal abundance of the

host organisms in the sea, particularly plankton. In 1972,

Colwell took a tenured professorship at the University of

Maryland. Her studies expanded to include investigations on

the impact of marine pollution at the microbial level. Among

her findings was that the presence of oil in estuarine and

open ocean water was associated with the numbers of bacte-

ria able to break down oil. She studied whether some types

of bacteria might be used to treat oil spills. Colwell and her

colleagues also made a discovery that held promise for

improving oyster yields in aquaculture—a bacterial film

Colonies of Penicillium notatus, showing surrounding zone of

bacterial inhibition. This is the phenomenon noted by Fleming in 1929,

that led to his discovery of Penicillin. Undated.

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