PMID:4886277

citation	Squires, CK and Ingraham, JL (1969) Mutant of Escherichia coli exhibiting a cold-sensitive phenotype for growth on lactose.J. Bacteriol. 97:488-94
abstract	As part of a study on the effect of low temperature on cellular regulatory processes, a class of lactose-negative mutants of Escherichia coli K-12 was isolated which could use lactose as a sole carbon and energy source at 37 C, but which could not use this sugar at 20 C. The lactose operon of the mutants functioned normally at 20 C. Galactose exhibited a strong inhibitory effect on growth, especially at 20 C. Growth of the mutants on glycerol was stopped at 20 C and slowed considerably at 37 C if galactose was added to the medium. Making the mutants galactose-positive eliminated the cold sensitivity of lactose utilization. One mutant was shown to be galactose-1-phosphate uridyl transferase-negative, galactose-kinase heat-sensitive, and uridine diphosphate-galactose-4-epimerase-positive. It is postulated that the mutant is able to phosphorylate galactose at 20 C (if only at a very low rate), but lacking transferase it is poisoned by the accumulation of galactose-1-phosphate. At 37 C, galactokinase is nonfunctional and the mutant grows on the glucose moiety of lactose.
links	PubMed
keywords	Enzyme Induction; Escherichia coli; Galactose; Galactosidases; Genetic Complementation Test; Genetics, Microbial; Glucose; Lactose; Membrane Transport Proteins; Molecular Biology; Mutation; Phosphotransferases; Temperature
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Main Points of the Paper

• Complementation of the gal genes is discussed
  • making the mutant gal⁺ corrects the cold sensitivity of lactose fermentation and overcomes the toxic response to galactose at low temperatures

Methods Used

• Parent strain: KG531-1 (his^-, met^-, thi^-, galT^-, strR, λ^R)
• 2-aminopurine (2-AP) mutagenesis
• β-galactosidase assay
• Galactosidase permease assay (uptake and hydrolysis of ONPG)
• Galactokinase assay
• P1 transductions

Annotations

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Species	Taxon ID	Strain	Gene (if known)	OMP	Phenotype	Details	Evidence	Notes
Escherichia coli	NCBI:562	K-III-4		cold-sensitive for growth on lactose-minimal plates	Growth	normal growth rates at 20C on glucose and at 37C on both glucose- and lactose- minimal media	Other	Table 2-Growth curve
Escherichia coli	NCBI:562	K-III-4		decrease synthesis of beta-gal	Metabolic Activity	differential rate of beta-galactosidase synthesis fell to a very low value shortly before the mass had doubled.	Biochemical Assay	Figure 1-LacZ assay vs. dry weight
Escherichia coli	NCBI:562	K-III-4		galactose-dependent toxicity at 20C and 37C (inhibition of growth)	Growth	the addition of galactose alone inhibited the growth of the mutant at both temperatures.	Other	Figure 2 and Table 6- Growth on galactose vs. lactose vs. glycerol at various temperatures
Escherichia coli	NCBI:562	K-III-4	galK	ts for galactokinase at 37C	Metabolic Activity	galactokinase-negative at 37C, but positive at 20C	Biochemical Assay	Tables 7 and 8
Escherichia coli	NCBI:562	K-III-4	galT	Cs for galactose-1-phosphate uridyl transferase at 20C	Metabolic Activity	galactose-1-phosphate uridyl transferase-negative at 20C, but positive at 37C	Biochemical Assay	Table 7- results of complementation tests
Escherichia coli	NCBI:562	KG531-1		reduced growth rate on galactose only	Growth	slight toxicity of galactose when grown at 20C and at 37C	Other	Figure 2-Growth curves comparing lactose, galactose, and glycerol at various temperatures
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