First Advisor

John W. Myers

Term of Graduation

Summer 1981

Date of Publication

7-15-1981

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Biology

Department

Biology

Language

English

Subjects

Escherichia coli

DOI

10.15760/etd.3124

Physical Description

1 online resource (3, 49 pages)

Abstract

Chromosomally determined arsenate resistance in Escherichia coli is well characterized. Little, however, is known about chromosomally determined arsenite resistance in E. coli. Accordingly, spontaneous arsenite resistant mutants were selected in a plasmid free strain of E. coli. One mutant strain was analyzed in detail, genetically and physiologically. The mutation confering arsenite resistance was shown to be a single gene mutation. Genetic mapping studies using conjugation and transduction showed that the mutation was closely linked to the ilv region of the E. coli map.

Physiological studies of this mutant showed that it shared characteristics common to those of mutants of E. coli defective in the membrane bound adenosine triphosphase (ATPase). Such cells are unable to generate ATP by oxidative phosphorylation, the major mechanism by which aerobic organisms obtain energy. As a result, these cells exhibit an inability to grow on non-fermentable carbon sources, a heightened sensitivity to streptomycin, lowered growth yields when grown aerobically in limiting concentrations of glucose, and an inability to grow anaerobically on glucose.

The arsenite resistance and the characteristics associated with a defective ATPase were shown to be the result of the same mutation. The arsenite resistance mapped in or near the operon coding for the subunits of the membrane bound ATPase. This operon is referred to as the unc operon, and is at map position 83.4 on the E. coli map, 0.7 units from the ilv locus, which maps at 84.1 units.

To gain an insight into the mechanism of arsenite toxicity in E. coli, ATP levels in the wild type strain and the arsenite resistant, uncoupled mutant were compared after treatment of the cells with arsenite. The effect of arsenite was to rapidly lower ATP levels in the wild type strain, whereas in the mutant strain, the levels of ATP, although lower to begin with, remained constant.

This work provides evidence that the effects of arsenite on E. coli cells is bacteriostatic rather than bacteriocidal. Arsenite inhibition of growth was shown to be reversible.

The implication that the ATPase is a target for arsenite toxicity is discussed.

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Comments

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Persistent Identifier

https://archives.pdx.edu/ds/psu/18142

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