Date of Graduation

12-2015

Document Type

Thesis

Degree Name

Master of Science in Physics (MS)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Pradeep Kumar

Committee Member

Ravi D. Barabote

Second Committee Member

Jiali Li

Third Committee Member

Woodrow L. Shew

Fourth Committee Member

Reeta Vyas

Keywords

Biological sciences, Bacterial response, Fluctuating pressure, High pressure, Reversibility of morphology

Abstract

We have studied morphological and genomic variations occurring in a mesophilic bacterium Escherichia coli (E. coli) in a wide range of continuous and fluctuating hydrostatic pressures. For all the studies here the temperature is maintained at 37◦C, the optimal growth tem- perature of E. coli at atmospheric pressure. Cell division is inhibited at high hydrostatic pressures resulting in an increase of cell length. The increase of cell-length depends on the extent and duration of the stress applied on bacterial cells. We have studied the effect of high pressure stress in three different conditions – (i) Wild-type cells (almost no genetic mutations), (ii) cells cloned with a plasmid DNA containing mreB gene under lac promoter (but no induction of the gene expression), and (iii) cells cloned with a plasmid DNA con- taining mreB gene with induction of the gene expression. We find that, the cellular response of the cells is different in the three cases studied here. Specifically, we find that, the wild- type bacteria with no addition of a plasmid DNA are stressed the least at high pressure as compared to bacterial cells containing plasmid DNA. Moreover, our results suggest that, the cells containing a plasmid DNA upon induction of the gene expression are stressed the most and exhibit higher propensity of lack of cell division at high pressure. We have quantified the propensity of lack of cell division in different conditions by quantifying the probability distribution of the cell length. We find that, the probability distribution of the length of bacterial cells with a plasmid DNA show multiple peaks whereas wild-type bacterial cells show single peaked distribution. Next, we applied the oscillatory pressure. We find that, the average cell-length of bacteria decreases with τ suggesting that, the elongation of cells at high pressure is reversible. It is observed that the average length (< l >) of the bacte- rial cells revert back to the length of the bacterial cells at atmospheric pressure for τ ≈ 20 minutes for all the cases studied here.

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