Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Molecular biology and molecular genetics

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beginning of the twentieth century, scientists had tentatively

linked a number of diseases with molds, but had not been able

to isolate the compounds responsible. With the discovery of

aflatoxin, scientists were able to provide proof of the undesir-

able effects of a mold.

Just because a particular mold can produce a mycotoxin

does not mean it always will. For example, Aspergillus flavus

has been safely used for many centuries in China in the pro-

duction of various cheeses and soy sauce. Aspergillus flavus

and related species are relatively common, and will grow on a

wide variety of substrates, including various food-stuffs and

animal feeds. However, the optimum conditions for vegetative

growth are different from those required for the production of

aflatoxin. The mycotoxin in this species is produced in largest

quantities at high moisture levels and moderate temperatures

on certain substrates. For a damaging amount of the toxin to

accumulate, about ten days at these conditions may be

required. Aflatoxin can be produced by A. flavusgrowing on

peanuts. However, A. flavuswill grow on cereal grains (such

as wheat, corn, barley, etc.), but the mycotoxin is not produced

on these growth media. Aflatoxin production is best prevented

by using appropriate storage techniques.

Other molds can produce other mycotoxins, which can

be just as problematical as aflatoxin. The term mycotoxin

can also include substances responsible for the death of bac-

teria, although these compounds are normally referred to as

antibiotics.

The molds do not only present humans with problems.

Certain types of cheeses are ripened by mold fungi. Indeed,

the molds responsible for this action have taken their names

from the cheeses they affect. Camembert is ripened by

Penicillium camemberti,and Roquefort is by P. roqueforti.

The Pencilliummold have another important use—the

production of antibiotics. Two species have been used for the

production of penicillin, the first antibiotic to be discovered:

Penicillium notatumand P. chrysogenum.The Penicillium

species can grow on different substrates, such as plants, cloth,

leather, paper, wood, tree bark, cork, animal dung, carcasses,

ink, syrup, seeds, and virtually any other item that is organic.

A characteristic that this mold does not share with many

other species is its capacity to survive at low temperatures. Its

growth rate is greatly reduced, but not to the extent of its com-

petition, so as the temperature rises the Penicilliumis able to

rapidly grow over new areas. However, this period of initial

growth can be slowed by the presence of other, competing

microorganisms. Most molds will have been killed by the

cold, but various bacteria may still be present. By releasing a

chemical into the environment capable of destroying these

bacteria, the competition is removed and growth of the

Penicilliumcan carry on. This bacteria killing chemical is now

recognized as penicillin.

The anti-bacterial qualities of penicillin were originally

discovered by Sanford Fleming in 1929. By careful selection

of the Penicilliumcultures used, the yield of antibiotic has

been increased many hundred fold since the first attempts of

commercial scale production during the 1930s.

Other molds are used in various industrial processes.

Aspergillusterreus is used to manufacture icatonic acid, which

is used in plastics production. Other molds are used in the pro-

duction of alcohol, a process that utilizes Rhizopus,which can

metabolize starch into glucose. The Rhizopusspecies can then

directly ferment the glucose to give alcohol, but they are not

efficient in this process, and at this point brewers yeast

(Saccharomyces cerevisiae)is usually added to ferment the

glucose much quicker. Other molds are used in the manufac-

ture of flavorings and chemical additives for food stuffs.

Cheese production has already been mentioned. It is

interesting to note that in previous times cheese was merely

left in a place where mold production was likely to occur.

However, in modern production cheeses are inoculated with a

pure cultureof the mold (some past techniques involved

adding a previously infected bit of cheese). Some of the mold

varieties used in cheese production are domesticated, and are

not found in the wild. In cheese production, the cultures are

frequently checked to ensure that no mutantshave arisen,

which could produce unpalatable flavors.

Some molds are important crop parasitesof species

such as corn and millet. A number of toxic molds grow on

straw and are responsible for diseases of livestock, including

facial eczema in sheep, and slobber syndrome in various graz-

ing animals. Some of the highly toxic chemicals are easy to

identify and detect; others are not. Appropriate and sensible

storage conditions, i.e., those not favoring the growth of fungi,

are an adequate control measure in most cases. If mold is sus-

pected then the use of anti fungal agents (fungicides) or

destruction of the infected straw are the best options.

See also Fermentation; Food preservation; Food safety;

Mycology; Yeast genetics; Yeast, infectious

MOLECULAR BIOLOGY AND MOLECULAR

GENETICSMolecular biology and molecular genetics

At its most fundamental level, molecular biology is the study

of biological molecules and the molecular basis of structure

and function in living organisms.

Molecular biology is an interdisciplinary approach to

understanding biological functions and regulation at the level

of molecules such as nucleic acids, proteins, and carbohy-

drates. Following the rapid advances in biological science

brought about by the development and advancement of the

Watson-Crick model of DNA(deoxyribonucleic acid) during

the 1950s and 1960s, molecular biologists studied genestruc-

ture and function in increasing detail. In addition to advances

in understanding genetic machinery and its regulation, molec-

ular biologists continue to make fundamental and powerful

discoveries regarding the structure and function of cells and of

the mechanisms of genetic transmission. The continued study

of these processes by molecular biologists and the advance-

ment of molecular biological techniques requires integration of

knowledge derived from physics, microbiology, mathematics,

genetics, biochemistry, cell biology and other scientific fields.

Molecular biology also involves organic chemistry,

physics, and biophysical chemistry as it deals with the physic-

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