On the relation of colony variants to the time dependency of colony formation during adaptive mutation of Escherichia coli FC40

1997 ◽  
Vol 43 (9) ◽  
pp. 884-886 ◽  
Author(s):  
Patricia R. MacLeod ◽  
Robert A. MacLeod
Keyword(s):  
Escherichia Coli ◽  
Carbon Source ◽  
Pure Culture ◽  
Colony Formation ◽  
Agar Medium ◽  
Selective Medium ◽  
Adaptive Mutation ◽  
Time Dependency ◽  
Colony Type ◽  
Selective Agar

When Escherichia coli FC40 formed adaptive Lac+ revenants on a selective agar medium containing lactose as the carbon source, the colonies which accumulated over several days were of two readily distinguishable types. Colonies of both types appeared both early and late on the plates. Cells of colonies that appeared early and late on the plates, irrespective of the type, when grown in liquid medium and replated, all formed colonies on the selective medium within 48 h. Cells of each colony type gave rise to colonies of both types and attempts to isolate cells of each type in pure culture were unsuccessful. It was concluded that the presence of two colony types in the cultures plated did not contribute to the observed time dependency of colony formation during adaptive mutation. The proportions of the two colony types arising from cultures of the Lac+ revertants varied from culture to culture.Key words: Escherichia coli FC40, variants, adaptive mutation, colony accumulation.

scholarly journals Ugp and PitA Participate in the Selection of PHO-Constitutive Mutants

2015 ◽  
Vol 197 (8) ◽  
pp. 1378-1385 ◽  
Author(s):  
Henrique Iglesias Neves ◽  
Tuanny Fernanda Pereira ◽  
Ezra Yagil ◽  
Beny Spira
Keyword(s):  
Alkaline Phosphatase ◽  
Carbon Source ◽  
Transport System ◽  
Constitutive Expression ◽  
Selective Medium ◽  
Adaptive Mutation ◽  
Pho Regulon ◽  
Content Type ◽  
Nutrient Sources ◽  
Selection Of

ABSTRACTMutations that cause the constitutive expression of the PHO regulon ofEscherichia colioccur either in thepstoperon or in thephoRgene, which encode, respectively, a high-affinity Pitransport system and a histidine kinase sensor protein. These mutations are normally selected on glycerol-2-phosphate (G2P) as the carbon source in the presence of excess Pi. The emergence of early PHO-constitutive mutants, which appear after growth for up to 48 h on selective medium, depends on the presence ofphoA, which codes for a periplasmic alkaline phosphatase, while late mutants, which appear after 48 h, depend both onphoAand on theugpoperon, which encodes a glycerophosphodiester transport system. The emergence of the late mutants hints at an adaptive mutation process. PHO-constitutivephoRmutants appear only in a host that is mutated inpitA, which encodes an alternative Pitransport system that does not belong to the PHO regulon. The conserved Thr217residue in the PhoR protein is essential for PHO repression.IMPORTANCEOne of the principal ways in which bacteria adapt to new nutrient sources is by acquiring mutations in key regulatory genes. The inability ofE. colito grow on G2P as a carbon source is used to select mutations that derepress the PHO regulon, a system of genes involved in the uptake of phosphorus-containing molecules. Mutations in thepstoperon or inphoRresult in the constitutive expression of the entire PHO regulon, including alkaline phosphatase, which hydrolyzes G2P. Here we demonstrate that theugpoperon, another member of the PHO regulon, is important for the selection of PHO-constitutive mutants under prolonged nutritional stress and thatphoRmutations can be selected only in bacteria lackingpitA, which encodes a secondary Pitransport system.

scholarly journals Caprylate-thallous agar medium for selectively isolating Serratia and its utility in the clinical laboratory

1976 ◽  
Vol 4 (3) ◽  
pp. 270-276
Author(s):  
M P Starr ◽  
P A Grimont ◽  
F Grimont ◽  
P B Starr
Keyword(s):  
Colony Formation ◽  
Octanoic Acid ◽  
High Efficiency ◽  
Clinical Laboratory ◽  
Agar Medium ◽  
Selective Medium ◽  
Bacterial Strains ◽  
Low Efficiency ◽  
Hospital Acquired ◽  
Very High

A defined agar medium (hereinafter designated caprylate-thallous [CT5 agar) containing 0.01% yeast extract, 0.1% caprylic (n-octanoic) acid, and 0.025% thallous sulfate is highly selective for all Serratia species and effectively discriminates against most non-Serratia strains likely to be in the same habitats. The selectivity of CT agar is demonstrated by the very high efficiency of colony formation (mean, 80.7% of that on a nonselective complex medium) on CT agar by known Serratia strains and the very low efficiency of colony formation (close to zero) on CT agar by bacterial strains known not to be Serratia. The utility of this medium in actual clinical laboratory practice is demonstrated by the more rapid and higher recovery of Serratia on this selective medium as compared to conventional procedures of in-tandem runs of 513 consecutive urine, feces, and sputum specimens. Pigmented and nonpigmented Serratia strains deliberately added to fecal specimens can be selectively and quantitatively recovered on CT agar. CT agar compares favorably with, or in some cases is an improvement over, other selective media which have been recommended for isolating Serratia. This selective CT agar medium could be quite useful in ecological surveys, especially those related to hospital-acquired infections.

scholarly journals A Semi-Selective agar medium to detect the presence of Xanthomonas axonopodis pv. malvacearum in naturally infected cotton seed

2005 ◽  
Vol 30 (5) ◽  
pp. 489-496 ◽  
Author(s):  
Yeshwant R Mehta ◽  
Cleide Bomfeti ◽  
Viviani Bolognini
Keyword(s):  
Cotton Seed ◽  
Agar Medium ◽  
Selective Medium ◽  
Detection Methods ◽  
Basic Medium ◽  
Infected Leaf ◽  
Xanthomonas Axonopodis ◽  
Selective Agar ◽  
Leaf Tissues ◽  
Final Composition

A semi-selective agar medium was developed for detection of Xanthomonas axonopodis pv. malvacearum (Xam) in cotton (Gossypium hirsutum) seed. The basic medium was peptone-sucrose-agar (PSA). Criteria for the semi-selective medium were the typical colony characters of Xam and its pathogenicity on cotton. Several systemic fungicides and antibiotics in different concentrations were tested alone or in combination with others. The final composition of the semi-selective agar medium was established after several attempts in order to inhibit most of the fungal and bacterial saprophytes and favour the development of Xam. It contained PSA + cyclohexamide, cephalexin, pencycuron, triadimenol and tolylfluanid. The bacteria were recovered from naturally infected seeds by the direct plating of 2,000 surface disinfected seeds on the semi-selective medium. The recovery of the pathogen from naturally infected leaf tissues and in dilution plating, on semi-selective medium and on nutrient agar, were comparable. Among the three detection methods tested, the semi-selective medium was found to be the most reliable and quantifiable. Degree of severity of angular leaf spot in the field was not always correlated with the level of infection in the seed. This is the first report of a semi-selective agar medium to detect the presence of Xam in naturally infected cotton seed.

Anaerobic incubation enhances the colony formation of a polA recB strain of Escherichia coli K-12

1982 ◽  
Vol 152 (1) ◽  
pp. 208-214
Author(s):  
M Morimyo
Keyword(s):  
Escherichia Coli ◽  
Saccharomyces Cerevisiae ◽  
Colony Formation ◽  
Superoxide Radical ◽  
Agar Medium ◽  
Oxygen Toxicity ◽  
Coli Strain ◽  
Permissive Temperature ◽  
Anaerobic Incubation ◽  
K 12

Escherichia coli strain E247 (polA1 recB21) has reduced colony formation (even at the permissive temperature of 30 degrees C) because of a poor suppressor mutation (sup-126). The colony formation was enhanced in the absence of oxygen about 3-fold at 30 degrees C and 10(6)-fold at 43 degrees C, suggesting that a polA recB strain was inviable due to oxygen toxicity. Colony formation was also increased by incubation in an agar medium containing the reducing agent thioglycolate and incubation in the presence of chloroform-killed Saccharomyces cerevisiae pet+ cells, but not pet cells. Since the E247 strain viability was inversely dependent on the oxygen pressure and since the strain was more sensitive to superoxide radical than either the polA or the recB mutant, it seems likely that the polA and recB genes play a role in repairing DNA damage during respiration.

scholarly journals Development of an Improved Selective Agar Medium for Isolation of Yersinia pestis

2003 ◽  
Vol 69 (10) ◽  
pp. 5787-5792 ◽  
Author(s):  
Raphael Ber ◽  
Emanuelle Mamroud ◽  
Moshe Aftalion ◽  
Avital Tidhar ◽  
David Gur ◽  
...  
Keyword(s):  
Yersinia Pestis ◽  
Quantitative Evaluation ◽  
Fluorescent Protein ◽  
Agar Medium ◽  
Brain Heart Infusion ◽  
Selective Medium ◽  
Bacterial Populations ◽  
Medium Components ◽  
Selective Agar ◽  
Green Fluorescent

ABSTRACT Existing media designed for selective isolation of clinically important members of the genus Yersinia were found to be unsatisfactory for the growth and isolation of Yersinia pestis. We report the development of a new selective agar medium (termed BIN) that supports the growth of Y. pestis. The development of the formulation of this medium was based on a fluorescence screening system designed for monitoring bacterial growth on semisolid media, using a green fluorescent protein-expressing strain. High-throughput combinatorial experiments can be conducted for the quantitative evaluation of the effect of different medium components on growth. Generation of fluorescence plots in this system, using microplates, allowed the quantitative evaluation of the growth rate of Y. pestis EV76 cultures in different agar compositions. The final BIN formulation is based on brain heart infusion agar, to which the selective agents irgasan, cholate salts, crystal violet, and nystatin were introduced. It was found that BIN agar is more efficient in supporting colony formation and recovery of Y. pestis than are the conventional semisolid media MacConkey agar and Yersinia-selective agar (cefsulodin-irgasan-novobiocin agar). The advantage of BIN over other media has been also demonstrated in recovering virulent Y. pestis from the mixed bacterial populations found in decaying carcasses of infected mice. The BIN medium is suggested as a selective medium for isolation and recovery of Y. pestis from various backgrounds.

scholarly journals Adaptive Mutation and Slow-Growing Revertants of an Escherichia coli lacZ Amber Mutant

Genetics ◽  
1996 ◽  
Vol 144 (4) ◽  
pp. 1337-1341 ◽  
Author(s):  
Michael J Prival ◽  
Thomas A Cebula
Keyword(s):  
Escherichia Coli ◽  
Cell Growth ◽  
Agar Medium ◽  
Convincing Evidence ◽  
Adaptive Mutation ◽  
F Plasmid ◽  
Amber Mutant ◽  
Fast Growing ◽  
Suppressor Mutants ◽  
Slow Growing

We have studied revertants, selected on lactose minimal agar medium, of the Escherichia coli lacZ  am strain that was first used by Cairns and his colleagues to demonstrate the phenomenon of “adaptive mutation.” We have found, by performing appropriate reconstruction studies, that most of the late-arising Lac+ revertants of this lac amber strain (appearing as colonies in 3–5 days) are slow-growing ochre suppressor mutants that probably existed in the culture prior to plating and cannot, therefore, be classified as “adaptive.” The appearance of a small number of fast-growing, late-arising Lac+ revertants may result from residual cell growth and turnover or from phenomena related to the fact that the lacZ  am mutation in strain SM195 is carried on an F′ plasmid. Thus, the appearance of late-arising revertants in this lacZ  am system does not provide convincing evidence that selective conditions specifically increase the rate of occurrence of favorable mutations.

scholarly journals Xylose-Lysine-Tergitol 4: An Improved Selective Agar Medium for the Isolation of Salmonella

1991 ◽  
Vol 70 (12) ◽  
pp. 2429-2432 ◽  
Author(s):  
RUSSELL G. MILLER ◽  
C.R. TATE ◽  
E.T. MALLINSON ◽  
J.A. SCHERRER
Keyword(s):  
Agar Medium ◽  
Selective Agar

Assessment of different selective agar media for enumeration and isolation ofListeriafrom dairy products

1988 ◽  
Vol 55 (4) ◽  
pp. 579-583 ◽  
Author(s):  
Lucas Dominguez ◽  
José Francisco Fernández ◽  
Victor Briones ◽  
José Luis Blanco ◽  
Guillermo Suárez
Keyword(s):  
Dairy Products ◽  
Agar Medium ◽  
Raw Milk ◽  
Superior Performance ◽  
Direct Plating ◽  
Selective Agar ◽  
Natural Microflora ◽  
Agar Media ◽  
The Difference ◽  
Better Than

SummaryDifferent selective agar media were compared for the recovery and isolation of five species ofListeriafrom raw milk and cheese. The selective media examined were Beerens medium, MacBride medium and that described by Dominguezet al.(1984) with 6 mg/1 acriflavine, listeria selective agar medium (LSAM), and LSAM with 12 mg/1 acriflavine (LSAM × 2A); a non-selective yeast glucose Lemco agar was included for comparison. When the difference between listeria and the natural microflora of raw milk and cheese was 102cfu/ml, listeria could be isolated by direct plating on all media tested. When it was lower than 103–104cfu/ml, listeria were isolated by direct plating only on LSAM and LSAM × 2A. When the difference was greater than 104cfu/ml, a previous enrichment was necessary to isolate them. LSAM and LSAM × 2A media performed better than the other media tested for isolating listeria by direct plating and improved their isolation from dairy products. This superior performance was evaluated by the ability of these media to support colony formation of different species ofListeriatested, the easy recognition of these colonies from those formed by other microorganisms and by their capacity to inhibit the natural microflora of these foods.

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