Black
Adaptation in bacteria
from Karstrom 1937
Maltose structure
Emerson 1945
The problem:
DNA is simple, boring stuff. It has only 4 constituents (GATC)
yet it is able to direct the formation of marvelously
complicated enzymes.
One view was that DNA acted as a putty or modeling clay and
made molds from which enzymes could be cast. This model
was described by Emerson in 1945.
Constitutive enzyme formation
Emerson 1945
Monod’s early work
From: The Emergence of Bacterial Genetics, by T. Brock:
"It is important to emphasize that Monod's gropings toward an
understanding of the mechanism of gene expression were
often erroneous.... it is essential that one not ignore his
blunders.
In the interests of simplification, and to avoid boring the
reader, history is often written as if it moves inexorably in a
single direction. Only after an event has transpired can we
discard all the erroneous ideas..”
Monod’s early work-diauxie
Type A sugarsNo diauxie. We will
call them primary
sugars (1o)
Type B sugarsShow diauxie. We will
call them secondary
sugars (2o)
Monod’s early work-diauxie
Isolation of Lac+ mutants
Massini and Neisser showed that Lac- E. coli could give rise
to Lac+ E. coli.
To do this they used indicator plates, similar to
MacConkey’s agar plates.
•These contain peptone (milk or meat peptides), bile
salts to keep organisms that are normally not in the gut
from growing, lactose (or some other sugar), a dye like
neutral red which is red under acidic conditions.
•When Lac- cells grow on MacConkey’s they use the
peptides for growth which makes the medium basic (from
NH4) and the colonies are white.
•on MacConkey’s Lac+ cells ferment the lactose during
growth which makes the medium acidic and the colonies
are red.
Lac+ and Lac- strains on MacConkey’s
Fecal bacteria on MacConkey’s
Some are Lac+
and some are
Lac-
Mal+ bacteria on MacConkey’s with maltose
Main colonies are Mal-.
Later, mutants which
are Mal+ grow and show
up as red papillae
From Shuman_NatRevGenet_2003
Adaptive enzyme formation
Emerson 1945