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 sugars- No diauxie. We will call them primary sugars (1 o ) Type B sugars- Show diauxie. We will call them secondary sugars (2 o )
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