Stimulation by X-Radiation of Enzyme Induction and Growth in Escherichia coli
Escherichia coli Al has been grown in a liquid medium containing, besides inorganic salts, glucose and amonium chloride as sole sources of carbon and nitrogen. The micro-organisms do not grow if maltose is substituted for glucose. Similarly, washed suspensions of E. coli which oxidize glucose vigorously have an insignificant O2-uptake with maltose. However, maltose is utilized for growth if NH4Cl is replaced by glutomic acid. Apparently the bacteria cannot form the enzyme needed to utilize maltose from their existing protein equipment but can if given a suitable organic nitrogen source. X radiation of 4 to 8 kr (190 Up, 10 ma, dose rate 8 kr/min) changes these conditions fundamentally. Washed suspensions of irradiated E. coli oxidize glucose as fast as controls, but unlike the controls, develop an increasing respiration in presence of maltose, the maximal rate (after 4 to 8 kr) being attained within 3 hr and approaching that for glucose. This response to maltose is suspressed by chloraraphenicol. Microorganisms viable after irradiation can grow on maltose in the liquid medium with NH4Cl, although slowly. The viable irradiated micro-organisms multiply with maltose and glutamate rauch faster than unirradiated controls for most of the logarithmic growth phase. This has been confirmed by turbidity measurements and plate counts. The response to maltose is lost on incubation of the bacteria with glucose and NA4Cl. Both controls and irradiated E. coli contain maltose. This has been demonstrated with ultrasonically disintegrated bacteria where the addition of maltose and glucose oxidase (notatin) caused an O2-uptake at equal rates in both samples. These results and further evidence justify the conclusion that the observed irradiation effects are due to the induction of permease for maltose in irradiated micro-organisms. If cells are subjected to ionizing radiations as they approach mitosis, chromosome changes are initiated which appear at metaphase as visible discontinuities of chromatid structure and as chromatid exchanges between different chromosomes. The discontinuities have previously been interpreted as suruiving examples of a much larger number of chromatid breaks produced at the time of irradiation, and the enchanges as the result of new unions between such breaks that occurred close together. Root meristem cells of the broad bean (Vicia faba), which had received 50 or 65 r of x rays, have been used to test a new interpretation of these changes, according to which each chromatid discontinuity arises from a chromatid exchange between two points close together on one chromosome. On this interpretation, the frequency of chromatid discontinuities at metaphase should be much lower than those of most other aberrations: it is shown that the high value usually obtained is due to the inclusion of a large proportion of short unstained but structurally continuous gaps, and that the frequency of true breaks is as low as the new hypothesis requires. It is accepted thnt radiation dosage and doseintensity experiments indicate that chromosomes suffer primary events at the points where and when they are crossed by the tracks of single ionizing particles; and also that, although themselves unstable, pairs of such primary events that sre close enough together in space and time can together enter a second stable state of exchange initiation. If the new hypothesis is also accepted it is argued to be unllkely that this primary ewent can be chromatid breakage, as is usually supposed, smd unlikely also that exchange initintion can be chromatid reunion. It follows that the chromatid exchange itself is structurally established at some later stage, as the two chromosome points continue their joint development in the affected condition.
- Research Organization:
- Univ. of Cambridge, Eng.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-14-000055
- OSTI ID:
- 4199385
- Journal Information:
- Proceedings of the Royal Society B: Biological Sciences, Vol. 150, Issue 941; Other Information: Orig. Receipt Date: 31-DEC-60; ISSN 0962-8452
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
AGE
AMINO ACIDS
AMMONIUM COMPOUNDS
ANTIBIOTICS
BACTERIA
CARBON
CHLORAMPHENICOL
CHLORIDES
CONTROL
DECOMPOSITION
ENZYMES
ESCHERICHIA COLI
GLUCOSE
GLUTAMIC ACID
IRRADIATION
LIQUIDS
MALTOSE
MEASURED VALUES
MICROORGANISMS
MITOSIS
NITROGEN
NUMERICALS
ORGANIC NITROGEN COMPOUNDS
OXIDATION
OXYGEN
PROTEINS
QUANTITY RATIO
RADIATION DOSES
RADIATION EFFECTS
REPRODUCTION
SALTS
SAMPLING
SUGARS
SUSPENSIONS
ULTRASONICS
USES
VARIATIONS
X RADIATION