Heterotrophic bacteria WORLD OF MICROBIOLOGY AND IMMUNOLOGY270•
phage DNA is single-stranded and some is circular. In 1962,
Hershey was named director of the Genetics Research Unit at
Cold Spring Harbor. He retired in 1974.
Hershey was “known to his colleagues as a quiet man
who avoids crowds and noise and most hectic social activi-
ties,” according to the report of the 1969 Nobel Prize in the 17
October 1969 New York Times.His hobbies were woodwork-
ing, reading, gardening, and sailing. He married Harriet
Davidson, a former research assistant, in 1945. She later
became an editor of the Cold Spring Harbor Symposia on
Quantitative Biology.Hershey and his wife had one son.
Hershey died at his home in Syosset, New York, at age 89.See alsoBacteriophage and bacteriophage typing; Molecular
biology and molecular genetics; Viral geneticsHHeterotrophic bacteriaETEROTROPHIC BACTERIA
Heterotrophic cells must ingest biomass to obtain their
energy and nutrition. In direct contrast, autotrophs are capa-
ble of assimilating diffuse, inorganic energy and materials,
and using these to synthesize biochemicals. Green plants, for
example, use sunlight and simple inorganic molecules to
photosynthesize organic matter. All heterotrophs have an
absolute dependence on the biological products of
autotrophs for their sustenance—they have no other source
of nourishment.
All animals are heterotrophs, as are most microorgan-
isms(the major exceptions being microscopic algae and blue-
green bacteria). Heterotrophs can be classified according to
the sorts of biomass that they eat. Animals that eat living
plants are known as herbivores, while those that eat other ani-
mals are known as carnivores. Many animals eat both plants
and animals, and these are known as omnivores. Animal para-
sitesare a special type of carnivore that are usually much
smaller than their prey, and do not usually kill the animals that
they feed upon.
Heterotrophic microorganisms mostly feed upon dead
plants and animals, and are known as decomposers. Some
animals also specialize on feeding on dead organic matter,
and are known as scavengers or detritivores. Even a few
vascular plants are heterotrophic, parasitizing the roots of
other plants and thereby obtaining their own nourishment.
These plants, which often lack chlorophyll, are known as
saprophytes.
Heterotrophic bacteria, therefore, are largely responsi-
ble for the process of organic matter decomposition. Many
pathogenic (disease-causing) bacteria are heterotrophs.
However, many species of heterotrophic bacteria are also
abundant in the environment and are considered normal flora
for human skin. The recycling of minerals in aquatic ecosys-
tems, especially in estuaries, is also made possible by het-
erotrophic bacteria. Although monitored by health officials,
the presence of heterotrophic bacteria in public water supplies
is seldom considered a public healththreat.See alsoAutotrophic bacteriaHETEROTROPHIC PLATE COUNT•see
LABORATORY TECHNIQUES IN MICROBIOLOGYHIGH EFFICIENCY PARTICULATE AIR
(HEPA) FILTER•seeFUME HOOD
HHistamineISTAMINE
Histamine is a hormone that is chemically similar to the hor-
mones serotonine, epinephrine, and norepinephrine. A hor-
mone is generally defined as a chemical produced by a certain
cell or tissue that causes a specific biological change or activ-
ity to occur in another cell or tissue located elsewhere in the
body. Specifically, histamine plays a role in localized immune
responses and in allergic reactions.
A select population of cells located in the brain manu-
factures histamine. After being made, the hormone is stored in
a number of cells (e.g., mast cells, basophils, enterochromaf-
fin cells).
Normally, there is a low level of histamine circulating in
the body. However, the release of histamine can be triggered
by an event such as a mosquito bite. Histamine causes the
inconvenient redness, swelling and itching associated with the
bite. For those with severe allergies, the sudden and more gen-
eralized release of histamine can be fatal (e.g., anaphylactic
shock).
Mast cell histamine has an important role in the reaction
of the immune systemto the presence of a compound to which
the body has developed an allergy. When released from mast
cells in a reaction to a material to which the immune system is
allergic, the hormone causes blood vessels to increase in diam-
eter (e.g., vasodilation) and to become more permeable to the
passage of fluid across the vessel wall. These effects are
apparent as a runny nose, sneezing, and watery eyes. Other
symptoms can include itching, burning and swelling in the
skin, headaches, plugged sinuses, stomach cramps, and diar-
rhea. Histamine can also be released into the lungs, where itTechnician working with bacterial cultures.womi_H 5/6/03 3:20 PM Page 270