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THE JOHN CURTIN SCHOOL OF MEDICAL RESEARCH CONTINUATION

 

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SYMPOSIUM ON GENETICS OF BACTERIA AND VIRUSES. John Curtin School of
Medical Research, Australian National University, Canberra, A.C.T.

August 19, 1957.

The permanent buildings of the Jéhnz Curtin School have just been completed
and occupied, and the symposium represented the firat function to be held

in these quarters.

PAPERS PRESENTED:

1. INTRODUCTORY REMARKS AND DISCUSSION.-- Prof, J. Lederberg, Dept. of
Medical Genetics, University of Wisconsin.

2, GENETICS OF PSEUD@HOWAS AERUGINOSA.-- Dr. Bruce Holloway, Dept. Bacterio-
logy, Melbourne Univ.

3. GENETICS OF INFLUENZA VIRUS. -- Sir MacFarlale Burnet, Director, Walter
and Eliza Hall Institute of Medical Research, Melbourne.

4. LYSOGENICIRY AND PROPHAGE~LINKED TRANSDUCTION IW BSCHERICHIA COLI. —

Dr. Esther M. Laditbers, Dept. of Genetics, University of Wisconsin.

5, GRYETICS OF VACCINIA VIRUSES. — Prof. Frank Fenner, Dept. of Microbiologg,
Australian National University.

6. GENETICS OF TOMATO SPOTTED WELT VIRUS. Dr. R. J. Best, Dept. of Agric.
Chemistry, Adelaide University.

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1. INTRODUCTORY REMARKS. A number of systems of genetic recombination have
been dm discovered in various bacteria during the past several years. In
Bscha@ichia coli, a sexual matin® frpcess has been found, by which large
blooks of genetic material are transferred from one cell to another in inti-
mate contact. Systems of genetic exchange in which only hereditary fragments
are exchanged haved been termed "transduction", The leading example, the
yumm transformation of prmumococcal types, was first discovered in 1928
by F. Griffith, and other workers have subsequently shwen that purified
preparations of deoxyribonucleic acid carry the genetic specificity. Another
mode of transduction, in which bacteriophage particles carry random bits
of genetic information, presumably as deoxyribonucleic acid, was reported im
x9H2x for Salmonella serotypes in 1952. MXNEXXXMAMEXERK It may well he the
basis for the distribution of various antigens in manifold combinations among
these types in aSUTG: SNES Seve er vr r ee SeenON Ae eae
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GENETICS OF PSEUDOMONAS. Recent findings indicate that the recombi-
national system of this bacterial genus is similar to sexuality in B. coli
in the following respects: mating type apecificity, loss of some genetic
markers during the cycle, and stimulation of mating by ultraviolet light.
A number of lysogenic strains have been found, but their inheritance in
crosses is still obscure. This is the first bacterial species after
E. coli in which sexual recombination has been delineated.

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LYSOGENICITY AND TRANSDUCTION. In E. coli, K-12, the phage “lambda”
is carried by certain so-called lysogenic strains. The ability to produce
this phage is inherited as a bacterial marker in bacterial crosses. Since
the lysogenic bacteria do not contain infective phage, but only préduce
it as a random event, or in response to mutagenic treatments, it is
considredto be carrying an Anlage of the phage, called a prophage (Lwoff).
The genetic experiments show that lambda-prophage is part of the bacterial
chromosome, linked to a cluster of genes for galactose~fermentation.

Free lambda particles occasionally carry with them the linked genes
for galactose-fermentation, hence can transduce these factors, but with
low efficiency, about 107 per phage farticle. The tranamig#ion of these
genes is analogous in many respects to the transmission of the prophage
itself to sensitive bacteria. Therefore, lysogenization, or the establishment
of a prophage, via infection, in a sensitive host is a category of trans-
duction, and the virus is in all essential respecta part of the hereditary
makeup of the cell. No mim fundamental feature xemmkux remains by which
we Gan strictly distinguish between a max virus and other genes, though
we emphasigethe infective transmission of a virus, in contrast to the
hereditary tmnemission of other genes in most instances,

INFLUENZA VIRUS. Dr. Burnet and his colleagues have stuiied the genetics
of influenza over many years, as reviewed in this account, Under certain
conditions of mixed infection sf (in chick chorioallantoic membranes, prin-
cipally de-embryonated eggs) with well marked strains, the following types
of interaction are founds 1) phenotypic mixing, in which particles of a
given genetic type are coated with a mosaicof outer (Aght#d71% antigen,
presumably during their emergence from the infected cells. These particles

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can therefore be neutralized by antiserum a@ainst either ane of the

perenthl straine; 2) kocera heterozygotes: these are single particles

which oarry the hereditary content of each patental strain, and therefore
give rise to mixed infections; 3) recombinants: these are pure-line par
ticles which receive part of their genetic scontant from one, part from

the other parent. The paucity of independehtly inherited markwrs has

limited the detailed genetic analysis of recombination. Particular attention.
has been given to the inheritance of virulence for chick embryos. xuxexxutayx
Grosses between highly and a~virulent strains give recombinant progeny

of a range of virulant types, as a rule considerable less virulent than
mtetk the virulent parent. The available data do not enable a decision
whether this "redistribution of virulence" depends on an ordinary poly—
genic determination, as in many quantitative traits in higher organisms,

or on the quantitative assortment of mgwetatx a°PS9iBlicated virulence
factor, as has alao been proposed{. Special interest attaches to these
stucies, not only as a pioneer treatment cf an animal vérus, but also
because influenaa contains ribonucleic acid, in contrast to tk deoxyribo-
nucleic scid basis of the heredity of 211 other biolofics1] material

ao far genetically studied.

POX VIRUSES. This group offers specisi advantages for genetic study,
as pure lines can be isolated with the help of single countable pocks on
ese menmbranfes.A number of strains of vaccinia(and of mouse péx)have been
examined, and found to differ in a variety of usable characteristics, such
as pook morzhology umi heat resistance and virulence, but not in serologic

reactions. A few disbinctiverecombinants have been found in mired infections,
in preliminary experiments to date.

BOMAZO SPOTTED WILT VIRUS. Very little work has been done so far on
the genetics of plant viruses, partly becaume of the difficulties of
contrélled mixed infection and isolation of pure lines. A few instances
of probable yecombination between distinctive strains of this vrrus were
deworibed,

These reports indicate that we are xskxxbex approaching the practical
experimental control of virus characteristics through controlled breeding,

but that much more fundamental information is still needed,
J. LEDERBERG

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