Microbiology and Immunology

Doolittle, W. Ford WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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The impermeability of the membrane is typically related

to the size of the particular ion. An ion can be too large to pass

through the pores of the membrane to the other side. The con-

centration of those ions that can pass freely though the mem-

brane is the same on both sides of the membrane. As well, the

total number of charged molecules on either side of the mem-

brane is equal.

A consequence of the selective permeability of the mem-

brane barrier is the development of an electrical potential

between the two sides of the membrane. The two solutions vary

in osmotic pressure, with one solution having more of a certain

type (species) or types of ion that does the other solution.

As a result, the passage of some ions across the mem-

brane will be promoted. In bacteria, for example, the passage

of potassium across the outer membrane of Gram-negative

bacteria occurs as a result of an established Donnan equilib-

rium between the external environment and the periplasmof

the bacterium. The potassium enters in an attempt to balance

the large amount of negative ion inside the cell. Since potas-

sium is freely permeable, it will tend to diffuse out again. The

inward movement of sodium corrects the imbalance. In the

absence of a Donnan equilibrium, the bulky sodium molecule

would not normally tend to move across the membrane and an

electrical potential would be created.

See alsoBiochemistry

DDoolittle, W. FordOOLITTLE, W. FORD(1942- )

American biochemist and evolutionary biologist

Ford Doolittle is a Professor in the Department of

Biochemistry at Dalhousie University in Halifax, Nova

Scotia, Canada. He is also Director of the Canadian Institute

of Advanced Research Program in Evolutionary Biology.

Doolittle is one of the world’s premier evolutionary biolo-

gists, who has used molecular techniques to explore the sim-

ilarities and disparities between the genetic material in a

variety of prokaryotic and eukaryotic organisms. In particu-

lar, his pioneering studies with the evolutionarily ancient

archaebacteria have led to a fundamental re-evaluation of the

so-called “tree of life.”

Doolittle was born in Urbana, Illinois. Following his

high school education, he received a B.A. in Biological

Sciences (magna cum laude) from Harvard College in 1963,

and a Ph.D. in Biological Sciences from Stanford University

in 1969. He was a Postdoctoral Fellow in Microbiology at the

University of Illinois from 1968 to 1969, and at the National

Jewish Hospital and Research Center in Denver from 1969 to

1971. From there he moved to Dalhousie University as an
      Assistant Professor in the Department of Biochemistry in


1972. He became an Associate Professor in 1976, and a
      Professor in 1982.
      Doolittle and his colleagues have made fundamental
      contributions to the field of evolutionary biology. Specifically,
      Doolittle has pioneered studies examining the origin of the
      nuclear genetic material in eukaryotic cells, the origin of the
      organizing genetic material known as introns, and the genetic

organization and regulation of the archaebacteria that inhabit

thermal hot springs. The latter bacteriaare among the most

ancient microorganismsknown, and knowledge of their

genetic composition and behavior has clarified the early

events of evolution.

From Doolittle’s research, it is now known that mito-

chondria, the so-called “powerhouse” of eukaryotic cells,

were once autonomous bacteria. Mitochondria arose from the

integration of the ancient bacteria and a eukaryote and the

establishment of a symbiotic relationship between the two. In

addition, prokaryotic cells may well have evolved by acquir-

ing genes from other species, even eukaryotes. This concept,

which Doolittle has dubbed lateral genetransfer, challenges a

fundamental pillar of evolution, which is the separateness of

the kingdoms of life. For example, a fundamental scientific

opposition to genetically modified organisms is that the acqui-

sition of eukaryotic genes by the altered bacteria violates evo-

lutionary laws.

Doolittle has received numerous awards and honors for

his research, including the Award of Excellence from the

Genetics Society of Canada and a fellowship in the Royal

Society of Canada.

See alsoArchaeobacteria; Bacterial kingdoms; Evolutionary

origin of bacteria and viruses

DDubos, René UBOS, RENÉ(1901-1982)

French-born American microbiologist

René Dubos was a distinguished microbiologist whose pio-

neering work with soil-dwelling bacteriapaved the way for

the development of life-saving antibiotic drugs. Widely

acclaimed for his discovery of tyrothricin, a chemical sub-

stance capable of destroying dangerous staphylococcus, pneu-

mococcus, and streptococcus bacteria in both humans and

animals, Dubos later turned to the study of tuberculosisand

the role of physiological, social, and environmental factors in

an individual’s susceptibility to infection. In the 1960s,

Dubos’s interest in the effects of the total environment on

human health and well-being prompted him to give up his lab-

oratory work at New York’s Rockefeller Institute for Medical

Research to concentrate on writing and lecturing on ecological

and humanitarian issues.

Over the years, Dubos produced a number of popular

books on scientific subjects, including So Human an Animal,

the 1968 Pulitzer-Prize winner for general nonfiction, and

Only One Earth: The Care and Maintenance of a Small

Planet, which formed the basis for the United Nations

Conference on the Human Environment in 1992. Dubos’s

greatest concern was not man’s inability to adapt to pollution,

noise, overcrowding, and the other problems of highly indus-

trialized societies, but rather the ease with which this adapta-

tion could occur and its ensuing cost to humanity. “It is not

man the ecological crisis threatens to destroy, but the quality

of human life,” Dubos wrote in Lifemagazine. “What we call

humanness is the expression of the interplay between man’s

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